TYPICAL BRITISH TWINS AND TRIPLES CRANKSHAFT ISSUES AND REFURBISHMENT
Now if you are considering moving down stairs and looking to increase your knowledge or angst then read on. Basically, most of my experience comes by way of the Triumph ,BSA and Norton twins and triples. My first being at age 19 with 2 x A10 BSA engines laid out on the floor and figuring the puzzle into one goer. My old man Jack, himself a jack of all trades was able to assist with a small booklet that had some info. Ignition timing etc. I had watched dad build his GMC bus motor 4 yrs earlier. My first effort wasn’t the best of engines for sure but it did carry me around for a couple of yrs. I was a 3rd yr apprentice electrician at the time. So the main thing to remember about any work around alloy cases is that heat is a good friend. Belting bearings in and out of gearbox or engine casings cold is best left to the less enlightened. In my time i can’t remember the number of damaged bearing recesses I have encountered. This sort of brutality will cause things like bearings coming loose due to less than effective interference fitment.
So the odd puller is handy, a basic 3 bolt steering wheel puller helps with the primary drive sprocket, some 4” 5/16 and 3’8 unf bolts are handy, a puller for the clutch hub on twins and the triple has a special sized one for it. A 3 finger timing pinion puller is nice but they can be fragile, I have lent 2 in the past , never to be seen again. So in this instance, heating the case and removing the crank from the timing side half can be done with pinion in place then with a small wedge/pincer type puller the pinion can be removed. They are not usually that tight. I use my air rattle drive to remove the crank nut. On bush motors BSA etc, this may work but is determined by the size of the journal as under size bushes can stop the gear coming through with the crank. On Triumphs the pinion nut is right hand thread but the cam nuts are left hand. BSA timing pinion nuts are left hand also. Most others are righty tighty - lefty loosey but the Norton gearbox sprocket nut is LH. I bought a cheapie ¾ drive socket set yrs ago and then with the sizes required I welded ½” drive sockets to them .This allows use in cases where a shaft extends, like gearbox sprockets. Much better than most of the feeble pressed steel so called factory tools available. I have deep sockets too but sizes are limited. Another home made tool I have is 2 x large sturdy G clamps with a 1” piece of old fork tube welded onto the fixed end and cutaway at different angles . These I use for a valve spring compressor. I had an over the counter style early on but it is in landfill somewhere. You may also wish to buy yourself at least one micrometer with a 1-2” range to measure the crank journals. Typically these journals are anywhere from 1 3/8” to 1 7/8”. One more thing , a torque wrench is handy, mine is a 3/8 drive for the less bulky sockets.
With crank out in a vise with jaw protection and conrods removed , some whithworth sockets most likely required, the journal can be measured . It is a matter of feel , light drag , no rock. Check in a few places around the journal. Most wear happens at the top /bottom of the journal. The specs here allow about ½ thou, 5 tenths of a thou but a few more tenths is usually acceptable. How did the rods feel before dismantling, side to side play for sure but rock ? Hold the rod to one side at the base, with one finger and feel for rock at the top, this should be minimum and if the rod bearings are still in good condition and journal wear minimum to nil, then rock will also be minimum. There may be some rock and the bearing shells may be worn and not the journal, only a micrometer can tell for sure. Triumphs have a nice wide shells and takes more wear to show rock than both Norton and in particular BSA, which have narrower shells. Funny as BSA have to rely on oil passage to the rods via a bush which can wear and therefore lose oil required by the rods. Sludge traps should always be cleaned regardless of the amount of wear and I use a ½” drive screwdriver blade ,a big one ,a Snapon piece. If you see a Snapon truck wave him over. Until I found this ½” driver they make, removing sludge traps was always a bit of a nightmare. More often than not drilling multiple holes and punching out the residue . I bought a 7/8 UNEF tap to cleanup the thread. I have never had any trouble since and with a small drill to relieve the punch mark, the rattle gun and a little heat never fails. To remove the trap tube itself I got a tap and a nut , a couple of threads cut first then remove the top crank bolt and use the nut as a puller. The traps are always part or completely full. The last crank I did recently from a ’70 Bonnie with about 12,000mile was very full. Obviously little oil changing went on by the original owner. The oil is your only filter without a spin on. This is why a removeable oil filter is a great thing. Nortons have a much bigger gallery than BSA or Triumph and in ’72 they added a replaceable filter. I have never seen a full Norton crank. Triples have small oilway drillings but have an internal replaceable filter inline before the oil gets to the crank. The drillings still need cleaning though , similar to the square fours.. Once the crank is clean, high pressure air , a can of carb clean and a long wire brush in the drill , much gouging and scraping and if the journals are on spec or it has been to the machine shop for a grind then one can reassemble the tube and nut. A dab of loctite on top bolt but not on the tube nut. You may be the one to visit this again. Make sure the oiling holes on the journals are clean. With a Norton crank 6 x 5/16 studs and nuts or 3/8 studs and nuts on the late 850 crank, out of the way a clean is simple. Best to fit new studs and nuts here as they have usually been punched and this affects the threads. I have seen an engine of a friend who did his Norton and forgot to loctite or punch the clamping studs on assembly and it was a mess. Removing and replacing main bearings may require pullers on a Triumph and definitely on a Norton. I heat the case and tap on a block of wood on something solid , like a concrete floor. The jarring and heat should get the outer ring or full bearing to drop. I use the BBQ to get a full heat and a bit extra around the bearing with MAP gas. A quick clean and while hot drop in the new bearing or bearing race and or crank assembly. No need at all to put bearings in the freezer? With Nortons I use a 10-11 ball high capacity on the timing side , same as I use in Triumph twin 750s. This allows end float capture and saves piddling about with setting end float on 2 roller bearings. I have seen many Nortons in original low mileage condition that have lots of crank end float and make a loud clap or whack when revved as the crank slides across. These would have had end float set at the factory and need it done again at 10-12,000 miles. So a high capacity ball it is for me and they have almost the same dynamic rating as a roller. On a BSA if the timing side main is worn and in need of a new bush I will have the crank ground to .008 instead of .010 then set up the case in a mill machine after the bush is fitted and bore bush for .0005 thats ½ a thou or less clearance . This gives a better tighter tolerance than grind .010 and fit .010 bush. If you have a bush made you may wish to clean up to whatever size you wish .003-.004 etc and not waste main bearing material. Lots of heat cycles and a couple of oil changes in the first few miles and a filter added is best here. Helps make sure the oil gets to the rods and not out the end of the bush.
Check the conrod housings for evidence of fretting ( caused by the shells moving) and may require the rods to be resized. Resizing is a must in BSA’s as the rod housing can and will show ovality because the factory didn’t bother to go with the more practised route of using steel rod caps until the last year of production. I use new conrod nuts where possible but unless the rod bolts are damaged I will reuse them except on triples .I have had two triple engines fail both at idle thankfully, when a rod bolt broke. One was still factory fit as far as I know and the other is a ’74 I still own and had done a freshen up and had started 2-3 times, then while setting the idle it went CLUNK and stopped. A tear down revealed a bolt snapped in the middle. Not a thread thing, so this time I fitted Carrillo rods after having 6lb removed from the crank, then balanced and boy does it react to the throttle. So always new bolts and nuts at a minimum with Triples , for me anyway. Norton rod bolts are a sturdy 3/8” and new nuts is all I see the need for here. If racing I go to better quality rods anyway. Most 5/16 bolt tensions call for 18-24 lb and I have a basic rule, ¼” -10lb, 5/16” 20lb and 3/8” 30lb. It seems to work