M33 shock absorber

[Rog1]

In a similar fashion to my clutch problem, https://www.bsaownersclub.co.uk/bsaoc_forum/index.php?topic=12461.msg66633#msg66633 I've found that my shock absorber nut was loose. Just like the clutch, the problem is that the splines on the crankshaft do not protrude from the face of the cush drive bearing sleeve; the lockwasher has nothing to secure it.

If (similar to last time) the clutch bearing sleeve is the wrong one, replacements are very thin on the ground; it doesn't look like I'll be riding the bike any time soon unless I can come up with an alternative fix (The correct clutch sleeve is also thin on the ground). So, is using thread locking compound an acceptable substitute for the clutch and shock absorber locknuts? If so, any particular one? The engine and clutch sprockets are out of line by about 1/8th"; what's the maximum amount they should be out of line?

[idie]

I use locktite to stop nut undoing, don't use to much or you won't be able to undo it next time. An 1/8 inch is to far out of line it will cause wear on the chain and sprockets. What size is the spacer that fits against the engine bearing it usually sticks out from the engine a very small amount, maybe its to long It's usually about 1/4 inch thick, if to thick it will push the sleeve to far up the shaft. On the sleeve how thick is the piece at the end, sometimes they are meant to be the spacer as well. Is yours a 4 lobe or 2 lobe sprocket.

[Rog1]

I use locktite to stop nut undoing, don't use to much or you won't be able to undo it next time. An 1/8 inch is to far out of line it will cause wear on the chain and sprockets. What size is the spacer that fits against the engine bearing it usually sticks out from the engine a very small amount, maybe its to long It's usually about 1/4 inch thick, if to thick it will push the sleeve to far up the shaft. On the sleeve how thick is the piece at the end, sometimes they are meant to be the spacer as well. Is yours a 4 lobe or 2 lobe sprocket.

I thought an 1/8th was a bit much, but it's the clutch sprocket that's further out, not the engine sprocket. The spacer is 0.302" thick. The sleeve is too thick on the end to be the spacer as well. It's a four lobe sprocket.

[idie]

It could be that the clutch centre is for a swinging arm gearbox. This doesn't explain why your cush drive sleeve is so far out on the drive shaft. When I next get into my garage I will measure up the cush drive parts that I have. I removed the 4 lobe set up on my M33 some years ago and fitted the 2 lobe fittings, I also have the 4 lobe fittings of a B31.

[Rog1]

Okay, thanks Idie.

[martinh10]

I'm assuming the M33 cush drive is similar to the B31/33. I had a similar problem with chain alignment (0.2") on my B31 (a true bitsa) with both the original 6-spring clutch and a Triumph-type 4-spring. I spent weeks trying to get to the bottom of this (prior to my BSAOC forum days) and never did. My engine, gearbox, engine plates etc all appeared to be standard and the same as all the others I looked at. I ended up making a new engine spacer 0.2" longer than standard, removing 0.2" from the outboard end of the cush drive bearing sleeve and taking 0.1" off each end of the spring (workshop with surface grinder required) to give correct thread engagement and chaincase cover clearance. A stepped nut allows the splined sleeve to slide outwards on the lobes (I'm in the process of making a spacer to limit this to half lobe height irrespective of spring strength). I wasn't entirely happy about moving the drive load 0.2" further away from the engine main bearing but expect it will be OK.
Maybe there's a B31 specialist out there who can tell me why I had this problem in the first place – would love to hear from you!

[JulianS]

I have posted this service bulletin before - basically from the 1956 (not Gold Star) models the primary drive was moved out by about 1/8 inch to allow fitting of the fully enclosed rear chaincase, this involve changes to the clutch centre sleeve and cush drive assembly. A mx of pre and post 1956 parts will cause misalignment.

[martinh10]

Thanks Julian, that explains it!
Although why the new 4-spring clutch was supplied for all 1949 an on B31's without offering two clutch centre options is a question I will be asking my supplier.

[Rog1]

Things are becoming slightly clearer...

[idie]

The splined drive shaft does not protrude beyond the sleeve. The lock washer has inverted tags that locate in the splines in the sleeve. The lock nut tightens up against the washer then the outside of the washer is bent up against the flat on the lock nut.  The sleeve is 44.5mm long and the flange on the end is 3.3mm

[Rog1]

The splined drive shaft does not protrude beyond the sleeve. The lock washer has inverted tags that locate in the splines in the sleeve. The lock nut tightens up against the washer then the outside of the washer is bent up against the flat on the lock nut.  The sleeve is 44.5mm long and the flange on the end is 3.3mm

Brilliant. My sleeve matches that to within 0.1mm, so I believe I have the right one. The lock washer I found behind the nut was flat, though it had the right spline cut outs. Thank you, idie. I will order the right lock washer.

It seems then I have a post 1956 clutch centre. I assembled the clutch minus the centre bearing, and the misalignment between the clutch sprocket and the crank sprocket came in at 1.82mm/0.07". I'll fully assemble the clutch and see what the figure is then. I see that there were three spacer thicknesses and a couple of shim thicknesses, so with a bit of luck I should be able to get the sprockets lined up; my spacer is of middlin' thickness. If I can't obtain the right spacer I'll get one made.

Just to make sure, is it okay to Loctite the clutch nut?

[idie]

I usually Loctite the nut but only a little don't cover all the thread or you will have to do what I did and heat it up to remove the nut. The problem with the lock washer is that as you tighten the nut the washer turns and the tags get flattened. I smear some grease on the end of the sleeve to hold the washer in place. I hope that you get it all sorted.

[MGI]

Purely as a matter of personal curiosity Idie, why would you revert to the earlier type of two lobe  cush drive when BSA went over to a four lobe arrangement? One would assume that there was a logical purpose in the change with advantages over the earlier type?

[JulianS]

The two lobe replace the four lobe type and was new for 1955 models. On parts bulletin 4L from September 1954.

Shown in second photo, the first just to show the date of the bulletin.

[idie]

No BSA had 4 lobe then went to 2 lobe. I personally think the 2 lobe works better. With the 4 lobe the slopes are quite steep. The 2 lobe has a more gradual slopes and I think a smoother take up. This just my personal observation riding without the outer chain case on.