TIPS FOR CLASSIC OWNERSHIP
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.
BASIC FOUR STROKE PRINCIPLES (SUCK-SQUEEZE-BANG-BLOW)
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.