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As with Nortons described in the Norton section, I favour fitting an oil gauge to all Triumph, BSA Twins and Tri/BSA Triples. The main reason in the twins is grit which is either introduced or carbon particles can cause the ball to not seat properly on the feed side of the twin plunger pump. Don’t be fooled into thinking when starting your Triumph and peer into the oil tank to check your oil flow that all is well. The return flow is the result of oil, being brought back to the tank via the return side the oil pump and nothing to do with the pressure side of the pump. If the pressure side of the pump is compromised with some grit and the ball is not sitting properly on the seat excess oil can flow by into the sump. But this compromises the pumps ability to create pressure for the crank. Not having an indicator at all on the engine (light or gauge) is not a wise move. So any grit can cause a loss of pressure even in the later type twin port pumps as the chambers are merely paralleled. The pump needs to be cleaned after removal, checked for vacuum and primed with oil before replacing. This loss of pressure can happen when changing oil especially in OIF models where, I suspect, after draining the frame oil reservoir, and refilling from a height of 2 feet, causes deposits to dislodge and can send it up to the pump, despite the filter (actually a screen). I have been fitting Norton type cartridge spin-on oil filters to all of my bikes for many years now.
Removing and refitting the feed line at the bottom of any oil tank can cause the same problem by introducing dirt. With OIF bikes I usually change the oil by draining and filling simultaneously, i.e., remove the plug and then start adding fresh oil. When you notice clear oil starting to show at the drain, fit the plug, and thus avoid the dumping effect. On OIF models, fitting an oil filter in the frame works great.71:72 will require changing to T140 bottom plate, cutting out the feed pipe inside the frame to clear the filter, and blocking the external feed. I have done this modification to many OIF bikes and it is great.
Poor pressure can also be caused by wear in the seat of the pump body in high mileage motors. Both feed and return can be affected and replacement is the only option. Poor seating on the return side will cause wet sumping and this manifests as; excessive exhaust smoking, excessive crankcase breathing, i.e. oily mess in the breather line, and obviously low levels in the oil tank. These symptoms are also present when an engine wet sumps over a period of time (i.e. fills crankcase with oil from the tank) depending on the pump condition. This is not normal in Triumph Twin plunger pumps but common in Triples, BSA Twins, and late Nortons. When the factory anti sump device fails, all have gear pumps, and it is also present in Morgo rotary gear pumps.
Gauges are great fitted to BSA Twins and Triples as both motors rely on good oil pressure as they have 1 plain main as is the case in BSA Twins and early Triumph 500’s or 2 plain mains as is the case with Triples, plus the rod bearings of course. All plain bearings need good pressure to survive. The BSA Twins have a short enough life span as it is, so fit a proper oil filter and gauge and change the oil every 1000 miles. With only screens to filter the oil in most Brit designs except Triples and late Nortons, the oil is your only filter so dump it regularly. Black oil means it is full of crap (carbon).
If you have just bought a new (old) bike, do a full service which includes removing the oil tank and cleaning it thoroughly. You can’t clean it in the frame, except of course OIF, because in most cases the drains are higher than the tank actual bottom. Remove, clean and blow oil line or replace it. Fit an oil gauge. Before fitting the timing cover, renew oil seals. Any seals will do for the cam points housing, but a quality seal such as Pioneer brand is a must for the crank. Cheap seals can blow or lip out and there goes the oil pressure. This is most likely to happen if revving the engine on a cold start up.
A Morgo rotary has so much volume that it can actually give useable oil pressure even if the seal is lipped over. Plunger pumps can be refurbished: if you can tack or glue a pump ball to a rod, you can seat it with compound. I find the plunger pumps are good. I have six Triumphs running Norton cranks and they all show as good or better oil pressure than my gear pump Nortons. Years ago, an old bloke in Brisbane (Alan Chance, now deceased), would hard chrome the plunger pistons of the pumps, they were great. Alan also hard chromed valve stems, intermediate gear pins, rocker shafts, cam followers, auto advance units - damn near everything. It made the motor just that much better. A note of caution, don’t grip the pump body in a vice as it will deform, then you will need a new one. Grab the square nut in the vice and put a bar through one of the fixing holes.
Now, how do you time the ignition? GOOD LUCK. We will cover that later. Be careful not to spit the intermediate wheel when checking the oil pump before refitting the timing cover. That’s a pain, but can be rectified with 3 sockets and a friend. We will cover that later. Never top up an unusually low oil tank before a ride. If it has wet sumped then you will have one messy bike as most of what is now excess oil, will have no place to be, except outside. If unsure add ½ to 1 pint if the tank is empty, then start and idle until near usual level is achieved then adjust the level. Remember these are dry sump engines, so it should only have about half a coffee cup of oil in the sump. With the gauge fitted and the motor hot, expect to see about 10lbs per 1000rpm. If the machine has been sitting for long periods, drain the engine sump if possible. Strain the oil if it is good or replace it.

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On most bikes up to ’79, ignition was supplied by either magneto or points coil. Magnetos were phased out mostly at the end of the pre-unit era, 1963. Triumph and BSA twins had gone to 4CA type points which used the spark quenching capacitor/condenser on the points plate. No capability was designed to individually adjust each cylinders timing and adjustment could only be found via the points gap. Truly horrendous. The next design 6CA were a lot better and allowed the individual cylinder adjustment by adding two banana shaped plates to the main round plate. The points and banana plates were both adjusted by offset screw. The condensers were relocated under the tank. The last 10CA style were used through ’68-’78 and had the points adjustment by a ‘V’ using a screw driver. Triumph introduced the Lucas electronic ignition in ‘79. No other British bike was factory supplied with them until then. Today the market has a few electronic systems to choose from, the most prominent being Boyer, Pazon and Tri Spark are two more and all offer units for twins, triples and in some cases unit singles.  They can also be got in analogue or digital form. Digital, being the best for electric start, where the voltage may drop to 8 volt or so and can cause a misfire and kick-back. The cheaper analogue units are fine for most cases and if you have a good original or upgraded charging system then there are few to no issues. It pays to keep any bikes on a proper trickle charge/tender when not using the bike often. As for timing these ignitions they are straight forward via supplied directions but in the case of the Boyer the twin static timing may be advanced and will cause minor kick-back. If so, retard slightly then check with timing light if possible on your model.
With points, the 4CA type are a disaster and not worth the effort and if you must persist then good luck. With Triumph twins, the exhaust cam which carries the mechanical advance has a locating pin so timing is easier. Once 38 degrees or 10mm BTDC on the firing cylinder (both valves closed) has been found and a quick check of points gap at 12-15 thousandths, use a set of pointy nose pliers to grab the cam and turn clockwise against the return springs. With ignition on and spark plug in its wire and lying on the head, look for spark at the end of the travel. This will be as the points are just opening. If there is more travel after spark then adjust the banana plate in the clock wise direction.
There are no locating pins on the Norton and BSA twins or the triples. Find Before Top Dead Centre (BTDC) timing mark or measure 28 degrees for the Norton. This unit spins anti-clockwise. Put the advance unit into the taper and nip up close to the required cam ramp to points. Check the cylinder, points and coil are correct with the wire colour. Turn over a few times and set points gaps. Find timing marks again on the cylinder with both valves closed. Try with pliers for points opening. If a points break can’t be found with adjustment return banana plate and main plate to centre positions. Move the advance unit slightly. Repeat until successful without using up all adjustment. Check other cylinder timing. A similar process is required for A50-A65 and they are also anti-clockwise except the 36 degree BTDC. The full advance degree required is due to the piston dome height. The 28 degree Norton has a shallow combustion chamber and flat top pistons so flame travel is quicker than the Triumph and BSA hemi designs with high dome pistons. They require earlier ignition to get the job done as the flame front is impeded by the piston crown. This applies to the triples as well. Timing the triples is similar to the non-pinned Norton and BSA but clockwise. There is good marking on the rotor to assist.
The easiest, of course, is to go electronic, set and forget. I still run points in some of my bikes but these are offset crank ‘V’ fire with modified points 10CA plates as I am too stingy to go special ignitions for these. Some have over 2,000 miles on them and I haven’t checked the points as they should be good for double that between services. The biggest problem with points systems is the mechanical advance wearing and causing poor idling due to gap changes.  So the odd smear of grease or drop of oil goes a long way.
With magnetos some replacement parts are available if you wish to have a go yourself but I prefer to send mine to a professional. Timing these is relatively simple as the points fit in a taper with a locating notch. The drive side is tapered so with the timing cover off and the magneto bolted back in, be sure of drive wheel travel in relation to engine travel, with the spark plugs in the leads and resting on the gear box or something metal find 38 degrees BTDC. Which cylinder not really important at this point as HT leads will be fitted to correct cylinder after timing. Turn the points in the correct direction until just coming onto the ramp. If auto advance, wedge advance open (springs tight) this will be full advance. Fit onto taper of magneto loosely then do up nut loosely. Using thin paper (cigarette is good) place in points. Move points to find just open (cigarette paper releases) then tap advance unit onto taper with small hammer and socket to seat, firm up bolt. Remove wedge and check that rotating the advance weights  sees points just breaking at full travel with engine still at the correct timing mark. Or ,leave the wedge in and rotate the engine back wards then forwards checking the paper in the points releasing and noticing the piston position. This may take a few times to get right. With a manual advance use the lever to  figure out full advance at the points end. Move cam against points direction which makes points open earlier (advancing) therefore moving cam ring away from rotating direction has the points opening later (retarding). Push or pull? Set the BTDC height, move  the points until they are just opening,  paper releasing  and tap the wheel onto the magneto taper, fit nut and tighten. Recheck.
360 degree twin magnetos have cam ring opening ramps 180 degrees apart but not always. Wear and manufacturing tolerances could see a few degrees difference between cylinder firing. This can be seen on single carb machines when one pipe is blued and the other ok, indicating incorrect timing on the blued pipe cylinder. Check the timing on both cylinders and adjust it slightly to compensate and get the ignition on both a little out instead of one cylinder way out.
With mag/dyno  or SR1 mags seen on most Singles up to 1963 the points are opened by a rubbing follower foot that pushes open the points. Like the Twin manual advance find the direction of the mag compared to the engine direction then set the timing, piston BTDC on compression. Then move cam plate against that direction with lever and cable , slack or tight? so the  cigarette paper just releases at the end of travel, full advance. Tap on the drive gear and check again. Big Singles typically use 7/16 to 1/2” BTDC.
Most magnetos are available nowadays with conversion to electronic ignition. The main problem with this is that the charging system may need to be upgraded to cope.
Good luck.
Brian Holzigal.

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Since the mid 70’s and multiple Commando ownership, I have been very unimpressed with the stock rocker line (plastic). When it comes off the banjo it may give you a hot-wet sensation. The obvious and popular upgrade is braided line to the rockers. This has a 3 fold benefit: no leaks and an oil pressure gauge that can easily be routed to positions off the handlebar clamps (in your face); with the gauge on braided lines, you can now pack your oil pressure relief valve spring until you raise your oil pressure from a paltry 15-20lbs, factory set, (so as to not blow the plastic line off), to 50lbs or so and your rod bearings will love you for it.
Importantly, now you can see if your anti wet sumping device, (if turned on manually, or the ball that is coming off the seat under vacuum), is open, when the bike fires up. You can now monitor your engines lifeblood, via the gauge.
All my Nortons have been set up this way for over 30 years. I have seen my bikes start up with no oil pressure in the past and a quick tap on the aftermarket anti drain valve with the back my pocket knife sees the needle jump up to 60-70lbs cold. I use 20-50w in the winter and 40-70w in the summer. The gauge tells you how well the cold oil is pulling through during the warm up. Use a good high zinc oil to protect your cam and followers.
A gauge will tell you if the oil is low as the needle will start to flutter, also poor seals or pump and rod bearing condition can be seen with low oil pressure even after packing the oil pressure relief valve. It is invaluable as no light or gauge indication was fitted to Norton twins.
One step better is to put a “T” with an oil pressure switch (a single terminal as the braided line is grounded) and a warning light in the headlamp for those darker rides. It is a lot cheaper than a set of rods/cases/cylinder, etc. I put gauges on my Triumphs too, especially Twins as there is always a chance of the pump being compromised by a bit of grit on the ball seat, especially after an oil change. On Triumph Twins a gauge can also tell you rod bearing condition as you can watch how long it takes to bleed out to zero after you stop.
Be in the know and fit a gauge: without one you’re flying blind. I have seen two Norton 1972 models blown apart due to tacho drive seizures, stripping the cam drive and filling the pump with swarf as on this model there is no case filter. This caused the pump to jam resulting in no oil pressure and with no oil pressure indicator the motor internals were set free. So be careful when adding lipped or better seals to the tach drive on Commandos. They may stop the aggravating leak but oil down the cable to compensate.

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Many times I’ve heard from owners, “but it wobbles at 70mph, it wanders.” Well these machines can have a problems but it can be rectified. I have fallen off a Trident, a T140, an A10 and a Suzuki 500 twin, ridden too hard, and or ridden with nylon tyres, but not a Norton. The flexi flyer, as it should be called is designed with a hinge: it’s called isolastics.
What gives a tingle free ride @ 4000RPM, can also give a ponderous handling ride. Have you ever noticed when pitching into a corner, how the rear wheel comes with you a moment later? The isolastic design was good but flawed. In 1979 I made and fitted a third isolastic mount under the swing arm. My mate Neil and I pondered on this a while and reasoned that, with three mounts, the swingarm load would be better supported if triangulated. I made it a reality and it works great. I have done it to many of my personal bikes. You don’t need the top mount with the third bottom mount. The Norvil top mount helps with the STD 2 mounts. My 3  mounts, reduce isolastic maintenance to almost zero. Anyway, even without this modification, by rebuilding your isolastics and adding extra buffers and shimming to only a few thou, , keeps the flop to a minimum. As the PTFE washers wear a bit, the tingles with a tighter than called for setup ,settles in. Obviously the best is to fit MK III type conversions if staying with the stock setup. The swingarm pivot pin wears (not the bushes, they rarely wear).
The swingarm pin /axle seems to corrode and pit  in the bush . As most Norton owners know, the swingarm pin becomes loose in the cradle. It is best is to remove the swingarm, drill 2 holes out wide, tap ¼-28, use plain nut with ½-28 bolt and weld nuts to cradle. Paint, refit the swingarm with new bolts and new pivot pin in place and tighten. End of story.
To fit an 18” wheel/tyre or not?  Go ahead, it looks better, fills the void, offers better tyre choices and won’t affect the handling. I know some say it causes cornering clearance problems, but if you measure typical tyre sizes used, say 90/90/19 front and 4.10/18, there is no or little difference in diameter. I know a 90/90 or 3.60-19 front seems small, but when practicing at a track day once, I had a lot of head weave in corners and when I consulted a tyre tech, he said it was over tyred and we fitted a 90/90 and the shakes were gone. I only talk about my experiences on these pages not someone else’s. When using 110/80/19 on the rear, as you probably would, there is ¼ inch difference in diameter to the 4.10-18 or 110/90/18 using Avons. I prefer to use rear shocks at least ¾ to 1” longer as it helps compensate for fat arses and keeps the bike more level when loaded and helps steering. A quality shock, tailored  to suit or a pair of A65 shocks from the 63-70 era. This helps the machine from becoming a chopper when loaded. Check with the shock manufacturers. Low touring bars also keep some of the weight up front to help control wander. Fit a good steering damper if you want to but not before you make sure of wheel true, tyre condition, tyre type, K81/TT100 were designed for this bike I believe, pressures, wheel bearing condition, and wheel balances: all the things you should have done first. As Norton’s have notoriously stiff forks there are plenty of mods for damping, etc, but at least check the forks for tweaks and bent tubes. Sighting across the plane of the fork might reveal twisted trees. At least loosen axle pinch bolts, lower clamps, bolts and pump the fork up and down ½ dozen times then retighten all, preferably with fork pulled down. The last thing after you measure wheel alignment (string line) and tracking (tie a broom handle to front & rear wheels sticking up and sight) is to fit taper head bearings. Buy taper equivalent to the metric balls fitted from a bearing shop. The ball bearings cannot be loaded and therefore cause steering to easily flop. Tapers should be fitted so that there is a minimum of tension, (not so floppy). It will probably solve the wander. Matter of fact, do it first, maybe you can live with the rest.

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As owners of these machines you may be familiar with fact that your bike has a full plain bush on the timing side of the crankcase. The bushes have a tendency to wear and sometimes quickly especially if vibration is harsh due to poor crank balance. Good oiling as talked about previously is important for a decent life. The best performance I have seen from a bush motor was an A65 ridden easily and serviced regularly. It had 50,000 miles on it. The worst performance was 1500 miles on a newly rebuilt motor that was flogged hard. If you have an A65 or A10 BSA, or a 350/500 Triumph ‘57 to ‘68, then read on.
A bush can give good service if set up right and tight, serviced every 1000 miles and  fitting  an oil filter. By fitting a gauge you can keep an eye on the crankshaft bearing condition and by fitting a Triumph piston type oil pressure relief valve then adding packing to the oil pressure relief valve if required, you can raise the oil pressure to 60-70lbs or so, thereby keeping a good film of oil between the crank journal and the bush. The problem is keeping that film. With minimum clearance between the bush and the crank journal, the bush should last a lot longer.  Cold start ups are important, so don’t rev the crap out of it until you see pressure on the gauge. The bigger the gap the less chance of keeping oil in the gap and the less available oil to transfer to the big end/rod bearings. When oil becomes scarce at the rod bearings due to losses at the bush, the rod shells wear quickly then more pressure is lost, a vicious circle. Until 1972, BSA did not fit steel rod caps like most other British makers. This helped with ovality in the conrod big end housing. This ovality also caused oil losses. When rebuilding aluminium capped rods have them checked and or resized, and fit new bolts and nuts. I like to have the crank main ground to .008/.018 /.028 etc. Then when I fit the corresponding .010 /.020 etc bush, ie, heat the case and drop in the bush, I am able to line  hone the bush with a modified Sunnen hone to give me .0005 oil clearance. This is also the right time to set crank end float. This setup spins easily with no perceptible up and down movement, but be careful running it in as plenty of heat cycles are required. This custom made hone cost me over $600 US . I have done it plenty of times so take no notice of what your expert mate thinks. After 10/12 standing heat cycles, plenty of ½ mile heat cycles will be needed, gradually building up. Another method is to set the timing side case up in a mill and bore to the required clearance. Before setting the end float to .005-.008”, whack the crank on each end with a heavy soft mallet after warming the cases. This seats the bush and roller bearings. Just fitting a .010 bush on a .010 grind usually ends up with a .002 or bigger oil clearance. Not a good starting point. Change the oil 3 to 4 times in the first 1000 miles, the more the better.
1972 also saw a cast iron body oil pump for BSA which also helped keep oil up to the crank. The standard rubbish aluminium pump loses oil pressure out of the joint faces when operating.

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Even today the Classic British machines are still very capable. 650 and bigger Twins are obviously better on the highways when needed, although most classic riders will avoid the 4 lanes. A 650 Triumph, as with most British Twins, can easily cope with 70 mph cruising with a gearing change. The best place for your machine to be is at 3500-4000 rpm when cruising at 65-70mph. This is fairly easily done with a sprocket change. This is achieved by raising the gearbox teeth from the 650's standard 19, to a 21 tooth. The 750 Triumph twin has 20 teeth fitted standard and gives around 65 @4000rpm. It will easily pull the extra tooth. This 21-46 or 47 will give a much more relaxed feel to the engine at a given road speed. This will make the engine last longer, make your ride less vibey and get a bit more mpg. Some cutting is required to fit a 21 tooth sprocket to a 650-750 Triumph Unit Twin but a BSA A65 is already notched to suit and they too will live longer and be more relaxing to ride. Off the line performance it not really affected that much but you probably gave up wheelies years ago. I have a 1974 650, stock except for Conti replica Megaphones, it has a 21 tooth front and 46 custom  rear and with aggressive launches off the line it can still make the front a bit light and will still do 110mph flat on the tank. So my mates gauge said. On a stock unit 650, a buzzy 60 mph at 4000rpm STD gearing to 70mph at 4000rpm is a nice change.
Nortons are no different as a 750 has 19t up front. Go to a 21t on them and they will be a better machine on the road. An 850 usually comes with higher gearing: both can pull 22 or even 23 teeth but it is a bit more stressful on the gearbox internals. Norton boxes should be checked and upgraded, especially if you get a slap from the kick lever on the back of your leg, or you see the kicker flapping backwards under power. This is a sign that the layshaft ball bearing is collapsing and can be dangerous as it may lock the gearbox. Besides replacing the layshaft ball with a roller, fit a .020 or so shim in the kicker shaft to reduce layshaft end play and replace the first gear bush as it is one of the worst for wear.. Both these remedies  will help prevent jumping out of first gear. Put 3 bushes instead of 2 in the high gear and machine internal grooves for wire piston type circlips. This will prevent the bushes from walking out. Worn mainshaft top gear bushes can also cause problems with the layshaft and have similar signs to a failing layshaft ball. Of course replace any suspect bush or bearing. The gears wear rapidly on Nortons to a point so hardening wear on the load face is not unusual. Also fit hydraulic  X seals for the kicker and gear shafts in the outer cover. If you are going racing or intend to give your Norton a bit of a hard time then an outrigger on the high gear might be a good idea. This helps reduce flexing of the mainshaft and will help keep shifts more positive. You would need to be able to lock the box in position: so using a primary belt system is the easiest way.  I did a modification to and old E Start primary making use of a Trident style tensioner and stock chain, another way. The design of the AMC and therefore Norton box is fine for 350-500's but is a bit weak for the 750's and bigger. Its main problem is the 2 piece layshaft. Triumph and BSA have full layshafts. The Triumph 5 speed boxes are a good thing and I put them in every custom I can afford to although be wary of the first few years. A factory redesign saw a complete new lay shaft assembly. The main culprits were the high gear layshaft and 1st gear layshaft dog.  Dragging clutches can also cause 1st gear drop outs. An oil encased stock Norton clutch may need cleaning twice a year if used regularly. With a compressor tool it’s and easy job.
On TRI -BSA I use the Taiwan plates and dress my pressed steel plates. You can get a 2 finger clutch with no slip or use of heavy springs by maximising the steel plate surface area. Use a thick glass plate or similar dead flat surface and some 400wet/dry paper to achieve this. Try to get 80% or more flat surface. You will be surprised how little you have now. More surface area means more grip and less pressure is required. Surface the pressure plate as well. Set the pressure plate runout (wobble) to as fine as possible and use standard springs. Never take the pressure nuts below the end, ie. don't expose the stud threads.

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THE DARK SIDE for many, electrics. Never fear, this won't make you an expert, remember (X is an unknown quantity - Spurt is a drip under pressure) so be carefull you may not wish to be called an expert. There are plenty. Nevertheless, read on if you would like to have a bit more understanding of your machine. If you have a better than factory perfectly restored classic and don't ride it then you won't need this info.

Don't knock Lucas too much: sure there were problems with some of their products but we are talking about stuff made many moons ago. When it was new it wasn't too bad. Obviously what is available today is streets ahead so no comparison should be made. Over the years I've found a lot of Lucas problems were actually attributed to owners whose knuckles dragged on the ground. Self imposed electrical carnage, such as leaving bare wires to short, taping up twisted and unsoldered joints, putting foil in the fuse or no fuse. Fuses blow for a reason, not usually through age. Things would be easier if a small 3 or 4 panel fuse box were installed but they weren't on Brit bikes so either add one next time or deal with a single inline type that most makers deem fit. If the fuse is blowing without even turning on the key switch then look at the old zener diode or wafer rectifier, try removing the connections from one device  at a time, (the horn feed is usually the only other thing directly connected to the battery before the key switch), pull the wires off it and try a new fuse. The old silicon wafer type rectifier often shorts out from twisting the diodes when tightening the central bolt. Check the knuckles for scrapes. The Zener shorts mainly because most are in the weather and build up rusty crud between the central pole and the casing, causing a short. It may clean up and be ok? If it is still blowing with these 3 things disconnected look at the main harness for signs of heat,  ie wires melted together. By the way if the bike has no power or lights etc, or stops suddenly, then it may be the ammeter, especially some Asian repops, they can go open circuit, no electron flow, you know. Open the headlight and bridge the terminals on the meter or put all the connections together. It will get you home. Ok, so if the fuse blows when turning  the key on, check the lights. Are they are off when it blows then check the feeds at places like brake switches, coils and in the headlight shell for poor insulation and shorting. If the fuse blows when using the brake then check under the rear mudguard where you may find frayed and shorting wires. This may be due to the rear tyre rubbing because of too big a tyre or too short a shock, or too lard an ass, in which case use a longer shock or a smaller tyre or lose a few lbs. If the fuse blows when the lights go on, again check the tail loom under the rear mudguard, or the hi/lo handlebar switch, some aftermarket switches are real rubbish.. That can be a problem. If not, then into the headlight, check the wiring and plug socket on the semi sealed beam: they can be a pain, sometimes shorting if insulation is poor but usually just lousy contacts ,so no flow. Separate the front loom from the tail loom under the seat when testing. It’s a process of elimination, good hunting..

Your charging will need some sort of  repair at some time. On alternator bikes, the main culprits are the Zener and the wafer bridge rectifier are prone to failure after 50-60yrs of use, vibration and weather, as mentioned. The rotating magnet (rotor)  is 1 of 2 parts that make up the alternator, the other being the stationary winding (stator). The rotor has 2 problems, one being reduced magnetism with age causing a lower output and the other being a loose centre. This happens because it has separate magnetic pole material from the hex shaped centre that goes on the crankshaft and then they're cast together in aluminium. Over time it starts to break up and can be heard as a knocking sound in the primary, mainly at idle. Worst case, it can come apart and pole, meaning rubbing the rotor to the stator and if left, can weld to and destroy the stator and in the worst case can twist the crank end, I have seen a few. The rotor/stator need an even air gap of at about .008”.  New rotors are welded design and have been available in the last 20yrs, they are unlikely to disintegrate like the originals. Modern stators come fully enclosed in epoxy, this encapsulation started in the unit era ’63 on and  are available in standard output 120 watt in 2 wire 6 pole single phase, the later 180w 2 wire or 200 watt 3 phase, 3 wire, 9 pole types as introduced with the 1979 Triumph T140, they both use the same rotor.  There are a few makers and they all seem to be fine. If staying Pos ground then you may wish to continue using the Zener diode but I at least opt for a replacement to the wafer rectifier with a block type bridge rectifier sold through electronic outlets. Normally rated at 20 to 30 amps and cheap, they are about 40mm square and about 12mm thick with 4 terminals, they are adequate even if you upgrade to a 180 watt winding but maybe do as Norton did on its EStart model with 180w rating and add a second Zener to cope with more heat dissipation. Negative ground could still be ok as the small box rectifier can wire either way and by using a Neg ground Zener from the 1979 Triumph if still available, normally a silver colour and the positive Zeners are usually goldish colour.. With the new alternators I like to upgrade to a combination electronic rectifier/regulator made to cope with outputs of modern alternators but make sure you get the correct wattage to suit stator output. The new regulator/rectifier allows you to wire positive or negative ground/earth.  This can all be put in some early machines such as alternator pre-unit Triumphs, AMC and RE stuff. Staying with the 120watt is best as most reg/rec units are designed for that, I prefer the Tympanium unit , made in Texas for the last 50yrs and I have never seen a failure when used with 120watt output. Podtronics and Boyer make reg/rec units also. Chris Zoch in NSW, 0424 011767, a name familiar to HMCCQ members for magneto repair also makes reg/recs for your alt bikes and regs for generator machines . Buy local. If you opt for a 180watt stator and are unsure of the reg/rec rating then fit an H4 headlight, these are usually 60w low beam and run during the day to be sure, the higher output should cope with the load.  The main thing to remember here is that older weaker alternators are putting out less than the rated output, new rotor/stator units will be up to scratch but depending on your cruising RPM dictated by overall gearing, the output on especially older alternators and new ones too will rarely be at peak output unless you ride at 5000rpm everywhere. The higher the revs the higher the output voltage. So if your reg/rec is rated to your alt output it will rarely be overworked. Owners of machines fitted with amp gauges are ahead of the game. These things may be a bit vague but can give you an  idea if your system is working or indeed overcharging or undercharging without lights. I prefer to use an amp gauge where possible. I have bought but not yet fitted, small digital voltmeters about the size of a typical Brit amp gauge which generally don’t have an internal light. Nice bright indication of battery/charge volts.


If you are rewiring your machine and not using a replacement loom, you will need at least a 3mm (10 amp) wire. Remember at 12 volts, a headlight of 60 watts will use 5 amps.  The 2 main loom wires from the headlight shell (ammeter) to the battery area need to be the biggest. This includes the ground wire which needs to be all the way from the battery onto the frame then to the headlight shell. Don't rely on the steering head bearings for a ground. Make off the terminals with a decent crimping tool and seal them with heat shrink that will keep moisture out of the joint and help to stop fracturing. Soldering the joint is good too but even though I've done both, I don't have a preference. Always leave a bit more than you need. A tight fit at the device will mean a broken wire sooner or later. Don't join wires in the loom under the taped wires and especially don't change colours under the tape or heat shrink. Use as many colours as you can afford, not just one unless permanently marked each end.


You may wish to go to an electronic ignition. These devices have become very reliable in the last 15- 20 yrs and there at least 4 makers of units for Twins. Triples and Singles. Remember the original analogue basic types do use more current and are voltage sensitive, ie poor starting with low battery. With no ammeter therefore no real idea of your charging system, if you develop a backfire after riding a while with the headlight on, turn the light off and if the bike starts to run better then the charge output is low and you probably need a rotor at a minimum. The stator usually works or it doesn’t. Analogues plus the coils will use up to 4 amps or 48 or so watts. If you have an original 120 watt system max output (at around 4000+rpm) you can see  where with the head light on, using 60 watts+ with an incandescent bulb, how it will overcome the output of a weak original system around town at lower rpms. Go to LED lamps you may get away with it. The digital ignition units may be better as they are low wattage users, and not so voltage sensitive, although they are quite a bit more expensive. With a stronger charge, analogue is fine. The size of the battery is generally  irrelevant if the charge is good but not too good. I run 4amp/hr batteries in many specials with no ill affects and have built many, many customs with the same and never had a problem that I have heard about. I do so and do recommend using the headlight on longish highway speeds where the engine is doing 3500-4000rpm. Big batteries were appropriate when charging systems were weak and if electric start is fitted.

If you have an older magneto ignition machine, you can nowadays upgrade to an electronic ignition that directly replaces it. If you want to ride a lot, you may think is it a good option. Pazon produce a housing  that takes a modern ignition, designed for K2F  3 point mounting, similar to what Norton fitted to late Atlas and early Commando models. There may still be  kits that go inside a maggie that produce a voltage and fire an electronic box and coil. Kirby Rowbotham? You may also decide to upgrade the old generator to an alternator replacement. Alton  produce these conversions. Not a bad option if a daily rider. I had an old Tri pre/unit set up with an electronic ignition and Alton alternator. Some machines even have electric starts being made for them. Modern age oldie. Alton and Colorado Norton Works for Commandos, Phil Pearson in UK for B33-B34etc, Shropshire Classics in UK for unit Triumph 650-750 twins. Dave Madigan in the US for triples. Non era cheap but may cost about the same you would lose on depreciation on a new bike in one year. A 16-18 or 20 amp/hr battery is required so good charging needed, it is beneficial but put on the trickle at home between rides is ok too as a bigun will last for days even with starting. I prefer my  generator machines to be rewired and fitted with modern regulators and in neg ground 12volt form. My Goldie with E Start is so fitted. They should handle the requirements of a digital ignition, if used with low load LED lighting, 12v neg having the largest LED range.

If you decide to go batteryless then you may need  a regulator/rectifier with a capacitor incorporated in its design. Boyer did/ does one and a unit called Mitymax was around  for use  with chopper builders years ago. If not try  a capacitor from the Norton commando models with a   modern rec/reg combo. You just need to have some way to smooth out the AC ripple. The battery normally helps with this job. The bridge rectifier doesn't quite produce a dead flat DC wave instead it leaves a minor ripple. This interferes with the ignition, points or electronic. The machine may start but won’t rev much off idle, like it has a rev limiter, so turn on the headlight, with the heavy load of a normal light filament it will but then be ok. A good charge is needed to prevent stalling when idling with the normal filament  lights on though. If you have LED bulbs then a capacitor would be required. When battery less, best with points or if you go digital ignition then make sure of reasonable  alternator output  and a capacitor.  I have upgraded a few of my machines to LED. I use a readily available $10 H4 semi sealed beam and an LED bulb with H4 fixing. Daylight almost. Most I use even have a fan motor in the high lumen types. 1157 dual tail light bulbs are common in LED. These bikes I have fitted LED to are either generator or early 120watt alternator bikes. Early in the alternator days with enclosed stators, pre Zener, they were 6volt. These had 3 leads on the alternator output, a pair went to the wafer rectifier and the third was straight to the headlight switch. Light filaments don’t care if the source is AC or DC. This was the method of voltage control. With 2 of these leads twisted together, a specific pairing, these older units become 12volt and good for about 100watt, so with a modern reg/ rec are a candidate for LED bulb conversion. The rotors on twins tend not to sit directly in the middle of the stator so intended specified outputs may be affected, lower. On the Tri/ Bsa triples the rotor is about 50% wider and does cover the whole of the stator so it should be getting the best results. The wide triple rotors are hard to come by, only the slim twin rotors are newly made. I have never seen a wide rotor come loose. If you are happy with the charge meaning the magnetism is still good  but find the rotor is loose (knock,knock) you could jump on the lathe and make two thick washers about 13/4” x ¼” and gouge a bit from each side of the rotor to clamp it, leaving the steel centre bit a few though lower to do so. Did it many times yonks ago when new brit bits were slim to none.         Happy fiddling, Brian

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Carbs are another source of pain. Typically the classic era Brits use Monobloc, concentric, and Mk 2, with the change to concentric happening in 1968, and the change to Mk 2 in 1979.  Monoblocs were the next evolutionary step from separate bowls with the bowl cast in one with the carb, hence mono-block. The concentric has the bowl moved under or concentrically placed below the carb. Both are available as new manufacture. They can also both be resleeved: that is when the worn body is bored to accept a new slide that has had a sleeve of either steel or brass pressed on to it. This results in a tighter fit in the bore and longer life. The original design was a no-no. Similar materials don't wear well against each other and only a few do - definitely not the pot metal used in Amal carbs. It has a tendency to gall and stick. Later MK 2 Amals had teflon coating on the slides and lasted a lot longer. The concentrics come as 926 series with 26-27mm bores. The 930 series have 28-30-32 mm choices and 936 series have 34-36-38 mm choices. Mk 2 have 30-32-34mm choices in a series and 36-38-40 mm choices in the bigger 10 series.

Keeping your carbs clean is the key. Where possible turn off the fuel at end of the street and let the fuel use up before turning off the bike. Or drain the fuel if you are not going to ride for a while. The varnish in unleaded fuel will be left as a gummy residue blocking all the air and fuel orifices, once the fuel evaporates. Only a full strip and clean will get you back on the road. The biggest problem is the idle jet in the concentric: in the monobloc and Mk2 they are removable. In the Mk1 concentric, compressed air and possibly a fine wire will be required to clean this jet which is located behind the horizontal low speed air mixture screw. A blocked pilot jet makes starting and idling difficult. Spit back is one indication of leaness.

The pilot jet and its air control screw basically take care of the engines idle. When transitioning to more throttle, the cutaway in the slide has a lot of say as to how the fuel gets mixed: typically a 2-2.5 or even a 3 slide for multi carbs and 3-3.5-4 cutaway for single carbs. As the throttle is opened more, the tapered needle attached to the slide passes fuel either too much, too little or just right depending on the position of the needle clip. This fuel has to come through the main jet. As the throttle gets to ¾, the engine is fully on the main jet as the needle has cleared its own needle jet.

Once cleaned and refitted with a new O ring take care not to over tighten and warp the flange, which can cause the slide to stick. Set the idle screws from 1 1/4 to 1 1/2 turns out from dead bottom and set the slides with the angled idle screws to about 1/16" open. Fire it up and if it doesn't idle then increase a bit at time til you get something. Wind the mixtures all the way in one at a time and the engine should slow and possibly stall as the air is reduced. If there is no difference or it picks up a bit then the idle jet is still blocked. If all is good then the engine will pick up speed as you turn the mixture screw out. Find a happy beat in the middle somewhere. Go back to the idle screws and take one at a time all the way out, noting what the other cylinder does. Then screw it back in till you hear the cylinder chime in. Do the same with the other, adding a bit or taking away a bit from either to get the required even idle. Standing behind and listening helps distinguish the fast and slow cylinders. Then set synchronization by adjusting freeplay on the outer cables, either watching or feeling the slides. At least 1/8” freeplay is needed so as not to hang up the slides and produce a fast idle. If the engine fails to settle to idle quickly then check for freeplay, bound or jammed cables, cables tied too tight to the frame or air leaks at the manifold. Air leaks can be tested with carb  cleaner sprayed on the manifold between the carb and head while the engine is running. On a Triple falling back to idle slowly is normal due to the heavy stock crank. Twisting carb pull rod rack may also cause the engine to drop back slowly, if so fit a light spring opposite to cable end.

Typical main jet sizes for 650 twins  are 190 with Mk1 and up to 260 on Monobloc. 750 Triumph is 190 or 200 and Triples use 150. You can put 160 in the middle.750 Norton uses 220 and the 850 as much as a 260. A 500 twin uses a 150 or 160. When determining single carb jetting, I halve one of  the Twins jets and add to it. Say a Bonneville has 200 mains and I have a Tiger single carb, 1/2 of 200 is 100 + 200 is 300, a good starting point.

Ethanol can be a problem now days mixed at 10 or 15 %. This requires more fuel to get an optimum fuel air ratio. I have found especially at idle you may need to increase idle jetting. It’s easier on carbs with removable jets. On the Mk 1 you would need to drill out the cast in the pilot jet slightly and fit a removable jet in the threaded hole of the idle circuit. 26 and 27mm Mark 1 carbs don’t have this option.

Remember that a carburettor fitted to a normally aspirated engine relies on air speed. This is the speed of the air rushing into the cylinder as the inlet valve opens and the piston is travelling down. This leaves a vacuum or negative air pressure inside the cylinder compared to a positive pressure outside so it is just filling a void that appeared. This will change with altitude. The oxygen content, the part that mixes with the fuel to burn, gets less the higher you go. Not unlike your lungs where the muscles pull apart the chest and air rushes in. So, as the air rushes in, it will pull any fuel available through any orifice available. This means through jets which are usually a set size, except the needle attached to the slide, which moves through a needle jet. This allows varying amounts of fuel to be pulled into the engine depending on its position. As the air pulls fuel it mixes together or atomises.

If you use another brand of carb on your classic British you may need to be careful where it came from. A 2 stroke carb in a previous life will be way too rich for 4 strokes. In the case of a Mikuni, say a 32mm, you will need to fit the correct 6DH3 needle jet and a 159 P2 needle or close to it to get a starting point. You will need a smaller main and, as they correspond to Amal mains, then go by the figures I gave and at least a 30-35 pilot for twin carbs and 35-40 for a single carb. Also remove the small air jet on the needle air bleed circuit. Look at the front of the carb and into the holes to locate this air jet. PWK, recently on the market, is a modified Keihin and is a good bolt and go, available in 27, 30, 32 and 34mm with flange or spigot mount.  Mark 2's are good but check for 2 stroke use. I like Dellorto but they are expensive and it is best to remove the pumper. Flat slides are good for modified bigger engines but also are expensive. Be careful to stay with about the same size carb as fitted from the factory as there is no real gain on a stock engine, and may even cause it lose power.

TR6 SS 001.JPG


Gearboxes, most bikes have got them, thankfully. What do you know about yours? Over the years I have had to come to grips with the problems encountered when building or restoring British motorcycles as a business and hobby. I will attempt to give those interested a quick over view and a few tips on 50’s thru 80’s Triumph, BSA and Norton AMC type boxes.
With the Triumph, firstly a 4 speed then in 1972 a 5 speed, they have proved to be quite robust. The main reason for this is the full mainshaft and full length layshaft design. The layshaft was carried by top hat bushes early on but had changed to Torrington needle roller bearings by the unit models. The upgrade conversion from bush to Torrington roller on this shaft is simple, just a matter of using the later parts, ie. appropriate Torrington needle rollers and thrust washers, 57-1606,57-1607, 57-1614, If the layshaft bearing surfaces are still within spec. The bronze bushes are pretty hard on the hardened shaft, believe it and wear it noticeably, mainly when the lube is low. So a change to needle roller may also mean a new or more serviceable shaft. Bushes are fine if the oil is checked regularly. A small grind clean up, then with new bushes made to suit, can also get you more service life from the original shaft. Also the shaft used with bushes is longer on the output sprocket side and will need to be shortened slightly (a thin cutoff wheel) to suit the capped length of the Torrington replacement bearing. The inner cover will not go home otherwise. The mainshaft runs in a ball on the timing side and through a bush in the high gear which carries the sprocket. This gear then runs on an RLS9 1 ¼” ball, this RLS9 is normally 1 1/8” but is ground internally to suit. I had one years ago that had been ground off centre, that sure caused a wobbly sprocket and some flapping of the chains. The same ball is used by the BSA A65 and Norton AMC gearbox. I always use a sealed bearing but remove one plastic seal. Leaving the seal in the outer side assists the main seal 57-0394 that the sprocket runs in. Before tightening the sprocket nut if doing a sprocket change only, run a bit of sealer on the shaft to stop oil leaking down the spline on 4 and especially early 5 speed without the large ‘O’ ring. Pre-unit boxes never had gaskets and don’t need them if the surfaces are good, just a good sealer. (Don’t use screwdrivers to pry covers apart, I prefer a soft mallet and always heat cases or covers before removing or fitting bearings. I use the BBQ after pressure washing.) Adding a gasket will just add end float to the layshaft on these pre-unit boxes. These 4 speed boxes can be a bit noisy in 2nd and 3rd gear as there are no bushes for the gears to run on the shafts. Just a hardened gear on a hardened shaft, with a few levels of Rockwell hardness between them, I have rarely seen galling on these components. If lube is checked then there are no problems. Only 2 bushes were used, one on the 1st gear and one in the output gear for the mainshaft, besides the early layshaft of course. The top gear bush does wear and may need replacing at some stage. Keep chains adjusted correctly to avoid rapid wear to this bush.                                                                                 With the 5 speed things are quieter as each free gear has a bush twixt it and shaft. The same mainshaft to layshaft centres were used in the 5 speed and the gear set is basically the same width, so a conversion from 4 to 5 can be done from about 1950 on.  Things can be a bit tight, a dremel and some patience may be needed. So obviously the full gear set, high gear bearing, sprocket, camplate, selector quadrant and gear lever plunger body all need to go over as well as the 2 plungers that pick and move the quadrant. They are slightly different.  It is possible to modify a 4 speed plunger body to 5 speed with welding and grinding to set travel limit, the 5 speed being a shorter lever travel.  I have done more than 40 conversions, sometimes using the welded up method.  Basically 4 and 5 speed gear sets are the same 1st and top gear ratio but tightened up because of another gear in the middle. Great in the hills. Not much gives trouble with either especially the ’75 on 5 speed which has a stronger layshaft set than the ’72 to ‘74. Three types of cover plates were used in the unit 650-750 where the mainshaft pokes into the primary. The early one basically continued with the long bronze bush of the pre-unit, late ‘60s saw a steel extended nose, as part of the gear and using a bigger seal. This stopped the seal wearing a groove in the bush even to the point of cutting the bush in 2. With the 5 speed, the seal runs directly on the mainshaft. Tridents and Rocket 3’s use the same gear set as the twins with a short mainshaft and a different clutch mechanism, of course. The R3 has a different kick start ratchet pair. Triple 4 speeds had no seal at the sprocket end and can leak down the bush when on the sidestand. A sprocket nut machined with a seal retainer can be found to fix this. When tightening the nut for the kicker ratchet gear it is ok to use a rattle gun, very sparingly, so long as the shaft has no clutch attached and can spin freely. I have seen a broken shaft thread using this method on a 5 speed shaft (costly) with clutch attached. I have seen the nuts come loose often, which is why I like to give them a light rattle. I have occasionally come across a broken tooth on the kicker quadrant gear from over enthusiastic operators. People? who think they have to smash start their bike. I have also witnessed people? smacking the gear lever down with the heel of the boot to engage 1st gear. Just push it into first. The Triumph 4 speed is kind of a crash box although all teeth are constant mesh. When changing  gears the  teeth protrude into the next gear with as many as 23 teeth trying to engage with each other for 1st, as can sometimes be heard when the clutch has a bit of drag.  Try pulling into 2nd then back to first, this slows the gearset down. Sometimes every second tooth is cut back to ease meshing on pairs where the number is even.                                                                                    The 5 speed is very modern with only 3 and 4 dogs used to couple gears. The early 5 speed can get damaged though if one doesn’t clear the clutch before starting and trying to engage 1st. If the clutch won’t clear, when kicking through with clutch lever pulled, start the bike and while holding in the clutch lever, roll off down a hill or get a push off and engage 1st gear with a few revs and the clutch lever in. When rolling a few blips usually sees the clutch free up. Make sure you have an escape route. I have done this many, many times but don’t attempt it if you are not confident. I have a 1974 650 bonnie with about 50,000 miles on it and it has an early 5 speed set. Only once have I had a problem when the shifting got tight and it turned out to be a bush moving in 3rd gear. Pressed back in with locktite and all is well since. This gearbox got plenty of work outs, carrying the front wheel off the lights, even with taller gearing or the odd practice day at Lakeside.  The 5 speed in the photos is an early type. The later upgraded set has a few wider gears and stronger 1st gear dog.
BSA pre-unit boxes and A series unit twins are sturdy gearboxes as well with similarly designed full main and layshafts. Using only 6 dogs to engage a gear, things go much smoother when swapping cogs. Again the earlier pre-units had bushed layshafts and were susceptible to wear due to the bronze bushes if low on oil. The BSA set in the photo has such damage to both ends of the shaft. It also has significant damage to the teeth possibly due to poor meshing from badly worn bushes. If this is happening it may be noisy in 1st 2nd and 3rd but all quiet in top. These boxes also have gears running on shafts with no bushes like the Triumph 4 speed so if a bit noisy in 2nd or 3rd check your oil level. Later pre-unit BSA boxes were installed with Torrington layshaft needles toward the end of the pre-unit era. A T2 stamping indicates 2 Torrington layshaft needle bearings, factory fitted. The thing with many pre-unit bikes is that people may do major work to the engine, often multiple times but fail to service or rebuild the gearbox. On both Triumph and BSA unit models as the engine comes apart so does the box so all is revealed and appropriate measures taken. My biggest gripe with BSA boxes is the kickstart gears, in particular the ratchet gear that engages with the kicker quadrant gear. It runs on an ill fitting bronze bush, they are always badly worn and flopping about to the point of causing slip or locking of the kicker lever. One look at a Triumph should have had the BSA mob doing something similar. The Triumph uses a steel sleeve which has a tighter fit and allows little rock and therefore little damage. The BSA is rubbish so if you are changing that gear @ $60 per, get a decent, closer fitting bush made. 5 speed conversions are available for your swingarm  pre-unit BSA  A or B model but not unit A65 stuff that I know of. The pre-unit cluster is made by Nova in UK and also TT Industries in NZ I believe. The A65 has a poorly designed fine splined gear lever shaft. Easily stripped by smashing into gear and often found welded on. A repair is available that requires cutting and welding. I have married part of an oriental machines shaft and lever to A65s before. Cut this bit off there and weld on here.
I have addressed some of this following article in a previous article on these tip pages. The Norton AMC gearbox as used in Commandos and earlier Atlas or hybrids didn’t change much although the AMC and their hybrids ie. P11 Norton etc, used different shell mounting holes. A few changes to ratios in the last ES models and different kickstart return spring location in earlier featherbed models but basically interchangeable. I have an Atlas shell in a Commando so don’t let anyone tell you it won’t fit. Just a different mainshaft and cable entry.  They are capable enough but I have seen more problems with these boxes than the others. Some suffer from hardness issues on the teeth, I have seen broken main and layshafts at the point where engineers thought an undercut was needed but in actual fact only weakened the shaft, a radius would surely have been stronger. They were first used in 20hp 350 machines and by the end 60hp 850cc engines were transmitting power through them. These gearboxes do change swiftly and cleanly when in good order as only 3 or 4 dogs need to engage gears. I have seen more bent AMC mainshafts than in Triumphs, mainly Commandos. To combat this, an out rigger bearing can be fitted between the sprocket and clutch. Maybe Norton owners like to wheelie more than Triumph owners or maybe the Triumph clutch just spun on the taper with abuse but the splined Norton shaft had no choice but to give somewhere else. Would’ve been nice if Triumph and BSA adopted the splined mainshaft to carry the clutch. I do have a splined pre-unit BSA mainshaft but it was limited. I have repaired countless Triumph boxes with damaged mainshaft tapers when the hub has spun.                                                                                Anyway, the Norton AMC has a 2 piece or split layshaft, basically 3“ of plain shaft inside the kicker shaft on a bush which in turn locates in 2 steel bushes in the inner and outer covers. Not the most ridgid design so attention to this area is wise when reconditioning the boxes. When overhauling one of these, besides changing the RLS9 1¼” top gear bearing and the ball on the kicker side, I fit the upgraded layshaft roller on the drive side. A 2 piece replacement for the ball, of which I have seen many breakup, mainly in Commandos and at a minimum as it is failing, it will cause the kick start lever to flick back and forwards under load or at worst lock the gearbox and therefore the rear wheel . Now that is a problem.  The gap in the case between the 2 drive side bearings is minimal and can split so have a good look when next inside. This can happen when someone feels they need to drive these bearings in, often tilting and tearing or splitting  the case, instead of heating and dropping in.  When changing to the layshaft roller, end float will need to be set and a thin washer will have to be made usually .010-.020” thick, sometimes thicker. Grab the kick shaft and try moving in and out?? Too much end float? This can help cause, along with other factors, 1st gear to drop out as you take off. Almost always the bush will need replacing in 1st gear as it is a big wheel with a little bush and wears quicker than the other bushes in these boxes.  So this worn bush, excessive end float and sometimes a dragging clutch can be a pain when moving off. Another problem with this box is that the top gear bush for the mainshaft is 2 short bushes, one long one or another short one added is better. The bush can have a tendency to “walk” out or in and wear away, especially when there is a slight bend in the mainshaft. If you intend to add another short bush or one long one then have a groove inside each end machined for a wire piston type circlip. This mod stops the bush walking. The kickstart ratchet pawl can wear and cause the kickstart to slip when loaded, they are cheap so fit a new one if a full rebuild is called for. Then there is the designed to fail multi splined kick start shaft and kicker arm. I have come across many of these welded on. The way it is machined minimises the area for stable clamping of the kickstart arm on the spline. With the load way outboard of the centre line, mainly a problem on the Commandos, it is not long before things get wobbly and start ruining your expensive muffler as well. I have replaced dozens of arms and shafts, keep it tight, they aren’t cheap. Take up the slack to compression and push start, don’t slam start. UK made levers hold up better.
Generally speaking these boxes mentioned are reasonably strong and reliable but as I said, in a pre-unit setting they are often neglected. When was the last time you changed your gearbox oil??
Beware when adjusting primary and rear chains. I had a friend who thought he would make a buck and save his mate a buck by doing some work on his Norton. He adjusted the chains but didn’t have it right because when he took it for a test ride, he rode off the gutter which saw the obviously too tight rear chain go very tight and pulled the back completely out of the gearbox. A cheap service it was not. The take away from this is to leave chains a bit loose if unsure.
There is not much detailed info here, no mention of different ratios either, just a few of the basic problems one may encounter. The era referred to here was about the end of British bike evolution as many of us know it and for the level of metallurgy, machining capability and slide rule technology, they do quite well really. As for me, I had small British bike shops for over 30 yrs and did all the repairs, the boxes talked about here are in my favourite rides.

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                 Four strokes over 720 degrees for one complete cycle.

It doesn’t matter how you get the inlet air fuel mixture in and the burnt gases out either by side valve , overhead valve pushrod or overhead cam, 2 ,3, 4 or 5  valves per cylinder, so long as what you have is in good working order. Valves well seated and rings sealed in the bore, then compression you will have.

     This is a basic idea of how it works.

The SUCK is created by the inlet cam opening the inlet valve ,usually just before the piston reaches TDC, Top Dead Centre, lets say 20deg BTDC ,( before top dead centre) then as the piston is going down the bore a vacuum is created and inlet fuel /air mixture rushes in to fill the void. This is normally aspirated. Not to be confused with other forms of cylinder filling when using a Supercharger or Turbo. They force the fuel /air mixture into the cylinder, under pressure.                                                                       

The SQUEEZE.  The inlet valve will then close somewhere after BDC and mid way back up the bore on the Squeeze stroke, lets say 50 degABDC.   (After Bottom Dead Centre).   Compression can’t happen until the inlet is closed and the exhaust valve will also be closed at this point. So with both valves closed and the piston squeezing the mixture, the ignition will happen mostly somewhere between ½” ( a big single) and ( 3/8” -5/16” a twin )  before TDC. This moment depends on things such as stroke and combustion design. The more Hemi the design the more lead time required for complete combustion. With the higher crown pistons of the hemi designs like Triumphs it will take longer for the flame front initiated by the spark plug to travel across the piston dome. A flatter combustion chamber with an accompanying flatter top piston won’t need as much ignition advanced time. Think hemi Triumph 650, firing @ 38 degrees before TDC or a Norton twin with flat top piston needing only 28degrees advance.

After the BANG with the piston shooting back down on its POWER stroke , somewhere between halfway down and BDC Bottom dead centre  the exhaust valve will open.  lets say 50deg BBDC.   ( Before Bottom Dead Centre)                                                                        The BLOW. This sees the exhaust gases then exiting via the exhaust valve as the piston rounds the bottom and is pushing up.   The exhaust valve doesn’t actually close until the piston goes over the top at around lets say 20 deg ATDC . This gives a period when both valves are open at once for a short  time ,known as the overlap. With actual cam opening and closing times different to these examples given, especially on race engines, this overlap can cause fuel air mixture to be seen coming back out the carb, mostly caused by opening the inlet valve a lot earlier than standard road valve timing.

So there you go , the  crank goes around twice,  the piston goes up and down a total of 4 times or strokes for one complete cycle. To achieve this, the cams are geared off the crank to travel at half the speed of the crank.

When you think of timing on an engine, as you will have gleaned there is the timing of the cams and their relationship to the piston position and then the ignition timing ,finding the optimum time to burn  the compressed mixture.

Now if you are going to have a go at setting your valve clearances always err on the loose side. Too tight a clearance can cause a loss of power, burnt valves and seats.


A BSA with a TRIUMPH clutch.

This is something I have done since my early learning years with old Pommie bikes, basically the only type I’ve ever had. Some may call that masochism, I call it a challenge. One day 43 yrs ago my brother Grant called, he had recently bought a BSA M21 chopper , you know the things , the sort of bikes built by our now gentle readers in their youth. Why chopperise an M21? It’s a good question. It was a clean bike, the usual 16” rear wheel, 6 “ over tubes and Sporty tank, that sort of thing trouble was the  clutch would not separate. We got into it and the short version is we found that the old 6 spring clutch hub had cracked in the key slot. This is the piece that sits on the taper of the mainshaft and 2 rows of ball bearings run on . Basically when the mainshaft nut was tightened on  the taper the hub expanded and grabbed the main drive plate via the double row balls . Full time drive, not that handy unless you are a veteran rider. This experience and setup problems on my then ’57 Road Rocket turned me away from the BSA 6 spring design and I started to fit Triumph 3 or 4 spring cush drive clutches to any BSA I owned from then on. Less fiddly to set up. I know lots of owners are ok with the originals but I mustn’t have the patience required. The update was done by the BSA factory at the end of the pre-unit era of singles and twins anyway and just needed a special conversion hub. This is available today at about $140 new. Had BSA admitted defeat on the fiddly 6 spring or maybe thought they should take some R&D load off buyers. I typically use a 3 spring cush centre which if good enough for a Trumpy 750, will surely do a pre-unit BSA. As for the mainshaft nut, the original big flange type used by BSA can easily be trimmed down in your lathe to fit nicely into the cush with close proximity to the cush inner ID. Works a treat. Triumph had to get away from the big compensating spring drive when they fitted alternators to the crankshaft on their twins and they made a 4 spring cush hub for that. The 3 spring type came in the unit era. I have also used a belt drive kit designed for Triumphs , utilising a 3 spring cush hub, on a BSA pre-unit single. Funny but the crank splines are so close as to be useable, as is the spline on a SQ 4 Ariel. Yep ,something in the works there too.

The thing about the old compensating spring and associated cam lobes is that I have seen a number of crank splines with varying amounts of spline damage. This caused by leaving the whole thing loose on the shaft instead of tightening up fully with the large locking nut. Flogged is what they are, almost to the point of removing all the spline on one crank  I have seen. Only minimum movement on the cam is needed to be an effective shock absorber. I have seen and had repaired this damage on BSA , Triumph and SQ 4 crank splines. In the case of my Goldie I just welded the compensating sprocket and fitted a 3 spring  Triumph cush drive clutch. Modern mid 20th century technology.  An A10 special I have also uses a 3 spring clutch.    See photo. Hub 1. On the left is an original 6 spring taper BSA hub with drive plate and some double row balls missing. In the middle is a conversion hub and on the right is std pre-unit Tri hub.  Hub 2. This is my A10 with Triumph 3 spring conversion. Hub 3. This is 2 pics of a sealed ball I have made . This requires making a top hat piece to fit in the chain wheel to take the ball bearing, this presses in where the roller race is normally. I have a couple in service using open belt drive.

I have seen many instances of taper hubs breaking free and causing damage on Triumph twins, mainly caused by ineffective tensioning possibly due to the owners knuckles being sore from dragging on the ground. I suspect. I use a rattle gun. This taper lock system has been used forever and seen in lots of road and dirt competition bikes with no problems, attention to detail when setting up is the key. The amount of exposed woodruff key being one of those details. To use a key or not, another good question, what is its purpose? I have had 2 taper problems myself, on a Trumpy 750 . First episode was a little jump over a speed bump. The  thing left me stranded 10 miles from home, the next time was 100 miles from home , on the highway coming home from Barbers Museum, it just let go. Was able to push it to a Waffle House, had a coffee and the staff watched it while I had to bum a ride home to get the F150, on the back of a mates new Hinckley Bonnie. Worst ride in my life. The seat designer was obviously an ex ironing board designer. Anyway, it turned out the nut was cracked . Missed it the first time, bummer, so, did I do it with the rattle gun? Be a first, but maybe. Hasn’t happened since. That was 20yrs ago and countless clutches worked on since.

Anyway in my humble opinion a conversion to a Triumph clutch is a worthy upgrade. I do have 2 BSA splined mainshafts though, some sort of an attempt at a better wheel, no tapers? Funny thing is they are the same spline as a Norton mainshaft spline. Norton clutches ain’t half bad either. I have one on Judes 500 AMC single.

Cheers,     Brian.    some more useless info.

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