I removed the primary chain cover from my M33 plunger today and noticed that the end of the crankshaft has been contacting the case as has the big peg nut that holds the cush drive. Last time the cover was off I changed the cork gasket for a new one which is about 3mm thick. Is this right or should it be more substantial?
I cleaned up the case and stuck some masking tape on the damaged area, ran the bike and checked inside. The tape had been cut by the crankshaft. I've examined the case and it hasn't taken a knock.
Any suggestions as to why this is happening?
(https://i.imgur.com/k8B2qZGl.jpg)
(https://i.imgur.com/ke5SrWwl.jpg)
(https://i.imgur.com/Yi0rRaXl.jpg)
I don't think the gasket on my M33 is any thicker then 3 mm. As the nut hasn't come undone I would check for end float on the crankshaft. All end float should be taken up when the cush drive is tightened. Unless something has happened to the spacer between the two drive side bearings. The spacer is about one inch thick. If the cush drive is not tight enough the spacer can get worn. This happened on my B33 but I only found this on stripping the engine for a rebuild.
I had a problem with this after fitting a 4-spring clutch to my plunger B31 and having to use a spacer behind the cush drive bearing sleeve to align the engine sprocket and clutch drum.
I stuck 2 gaskets together with silicone. The primary case screws were just long enough.
You could probably also use a thicker gasket at the chaincase to crankcase although you may also need to pack out the distance sleeve behind the inner primary case, where the footrest stud runs, to keep things "square".
If I remember correctly , this was the solution on my M21, also with a 4-spring clutch. Clearance behind the chainwheel was not a problem.
I would try the 2 gaskets first to save stripping the whole primary ;D
Cheers
Pete
Pete
I've spent some time staring at the cush drive arrangement on the bike and perusing all the BSA literature I've got and decided that an engine rebuild is possibly in my future. So far as I can tell, the only way this wear can happen is for more of the drive side crankpin to have emerged from the crank cases because it didn't used to be like this. That said, my worry is that the con-rod won't now be properly lined up in the barrel and will cause issues there next. I suspect it's the spacer idie referred to.
I also can't see any evidence of a lock-washer behind that big cush drive securing nut. Hmm.
It's a shame as I had just got it ready for outings when regulations allow and I won't have space to work on the bike for a while as a friend's bike is currently dismantled in the workshop. I've still got my Guzzis to ride but I'll miss the BSA which is so light in comparison.
Hello everyone. I've decided to resurrect the ancient thread I started because, after all this time, I've finally had a chance to look into this properly. The bike has just stood there all this time gathering a layer of dust.
Having stripped the engine as far as removing the barrel I can confirm that there is no unnecessary end float in the crank shaft and the con rod is nicely central to the barrel opening. It seems that Pete C had the right answer all along. The bike has been fitted with a 4-spring clutch and a spacer used to correct chain alignment.
I've added a spacer of thick gasket material between the primary drive and crank cases and behind the spacer on the footrest bar. A dry run showed this had done the trick so it'll all come apart again soon to be done properly.
Interestingly there was no lock washer behind the cush-drive nut (was tight) or behind the clutch centre nut (was loose but no damage done). Various other felt/cork seals were missing as well.
I've made a peg drive socket to fit the cush-drive nut but can't find any torque settings for it so I'll just do it up gud'n'tite.
I had a similar problem when I fitted a 4-spring clutch to my plunger B31. I had to move the engine sprocket almost .200" outboard to align the chain (I'd be interested to know by how much others have had to move the engine sprocket). My B31 is a proper bitsa and even after a lot of head scratching I never did get to the bottom of it - even a 6-spring clutch didn't line up. Anyway, I did pretty much what you have done - moved the whole primary chaincase outboard but in my case about 3/16"with alloy spacers between the chaincase and the crankcase and the footrest tube and the engine plate (see photo). The scroll on the sliding plate came in about right place on the clutch sleeve.
I wasn't entirely happy about moving the drive load so far away from the LH crank bearing but the way it gets ridden these days I don't expect it to be a problem - none so far anyway.
Thanks Martinh10. I think I've decided to make an alloy spacer to replace the thick gasket material. Yours looks very neat. I reckon the spacer the previous owner fitted behind the engine sprocket was about the same as yours.
One thing I forgot to mention John, moving the sprocket outboard by so much reduced the sprocket nut thread engagement to an unacceptable level. To remedy this I reduced the length of what is referred to by BSA as the cush drive bearing (65-2523) by .200" and in order to maintain correct cush drive spring compression (and hence operation) had a couple of mm taken of each end of the spring by a chap with a surface grinder. Whether this was strictly necessary I'm not sure. Hopefully you still have good thread engagement and can avoid this complication.