Primary Chain Alignment

[Lindsay S]

OK, I know it has been covered in detail elsewhere on this forum but I thought I would share my experience of an out-of-line primary chain and the solution for anyone who has the same problem.
My ‘58 Flash has had a change of engine at some time in its life and may have been converted from a six spring to four spring clutch but whatever the case, I discovered that the engine sprocket was 1/8” further forward than the clutch sprocket.
It would appear that there are two versions of the cush drive sleeve (42-69), one with a 5/16” flange; the one I had, and the other with a 3/16” flange; the one I needed.
I managed to obtain a new old stock sleeve with the narrow flange from an eBay supplier; problem solved!
The way my chain was running would have tended to push the crankshaft to the right, causing extra wear to the thrust face of the timing-side bush.
I have posted a picture of the two different sleeves below plus a picture of the NOS sleeve as I received it with its coat of protective wax!

[BagONails]

I don't know what kind of wax they used down Armoury Road back then but it sure stood the test of time. That's a standard of protection an ancient Egyptian would be proud of! Glad you found the solution Lindsay.  When I had this problem I also found a change of cush drive sleeve to be required but somehow my cush spring movement ended up reduced by about 30% although there are no signs of a problem thus far.

Just problems elsewhere! 

[Lindsay S]

The sleeve was almost perfect underneath all that stuff, with just one or two very small stains and certainly no rust. BSA must have been looking way into the future!
I’m curious to know when and why the chain line in the primary chain case got changed. I guess that, in the day, you would have gone into a BSA service department, quoted your engine number and be given the correct part (in theory!) but here we are sixty some odd years down the road and many of our bikes have been ‘mixed and matched’ (and in the case of my bike, not very well!), so unless you can be absolutely certain that your bike is 100% original, frame and engine numbers can be useless when it comes to to such things!

[JulianS]

The thin flange sleeves (BSA called them the cush drive bearing) were used on the 1954/55 swinging arm models. 1 for  1954 and 4 lobe cush and one for 1955 with 2 lobe cush. These years were not fitted with the steel plate between the front of the primary chaincase and the crankcase. These were fitted with 6 spring clutch sleeve part 65 3873.

The steel plate was added for 1956 models and it gave clearance between the front of the tin rear chain case and the gearbox. The primary chain line was moved out with the thick flange sleeve and new 6 spring clutch sleeve 41 3107.

So 2 different 6 spring clutch sleeves. The parts between 1954/55 and 1956 get easily mixed up over the years and with autojumble/ebay items.

The 4 spring clutch sleeve, part 42 3170 gives the same alignment as 41 3107.

[limeyrob]

Yes, my bike came with the primary drive in a basket, well 3/4 of it and a 1/4 of something else.  I fitted a 4 spring clutch and found it needed about 20 thou of spacers to get the chain aligned.  It had been missing the cush drive and I got one off e-bay so its seems I was lucky.  Recently I got a 23T engine sprocket (NOS MCA) and noticed it had a raised flange about 20 thou and sure enough it lined up spot on with no shims.

[BagONails]

Indeed, I ended up with a 5/16" cush bearing (8mm) all dims as per my sketch attached but the four spring clutch still wasn't quite right and I had to machine the clutch adapter taper to get it to go on enough for things to line up. My original 3/16 bearing was putting it even more out of line as you can imagine. I still ended up with a hybrid I think because of the reduced room for the cush spring and there was enough thread showing on the crankshaft that I managed to make and assemble an additional lock nut behind the new original type cush nut. I'm not worried about it now as its done a few thousand and the primary and clutch are excellent, I still haven't had to re-tension the primary chain.  The focus has moved to the top end now... 

[Lindsay S]

Thanks Julian, I knew someone would have the answer!
Mine was registered early 1958 so, depending on when BSA changed from ‘57 to ‘58, my bike could possibly be a 1957 model. It has the steel plate between the inner chain case and the crankcase and it very likely had a six spring because the four spring that is fitted now has a ‘new’ look to it.
What a story these things would tell if they could speak!

[JulianS]

The 1958 season bikes had frame numbers commencing FA7. 1957 season frame numbers commencing EA7. The first of the 1958 season bikes left BSA in October 1957.

[Lindsay S]

Mine will be a ‘58 then.