A7 Shims

[BSA500]

What is it with the shims on these engines this is the fourth time I have had to replace them. I set them up with about 1 to 1.5 thou clearance and after a few years they get torn up. The shock absorber nut is always tight the timing side bush is unworn etc. The bigest hassle is not just the splitting of the engine but the fact the debris normally buggers up the drive side bearing which again is hardly worn. The only upside is that I can split an A7 engine down in under 3 hours. I use it every day 26 miles a day and other than the vibration it was running really well. Rant over.

[bsa- bill]

don't take offence if this is obvious to you BSA500, but we have had shims on the wrong side of the bearing before, the shims go between the bearing and the crank web, the crank web, the shims and the bearing inner should all be moving together as one so no wear should occur to the shims unless something moves that shouldn't, like perhaps the bearing is not tight on the crank?

[BSA500]

No offence taken. The shims are where they should be(or what was left of them:)). I will check the bearing fit although a new one is going on due to bits of burnt tinfoil wrapped around the rollers

[manosound]

I learned this here (maybe you did too; maybe you taught it): Grind out a bit of the I.D. on the old bearing and use is as the test bearing when coming up with the correct shim thickness.

Richard L.

[MG]

Just a thought, but is the distance piece on the crank fitted the right way 'round (ie chamfer facing inwards)?

Cheers, Markus

[BSA500]

Ypep distance piece the right way round. Set up the crank last nught,well tried to takes ages. Found the bearing isn't as tight as it should be so will have sort it

[MG]

It is not uncommon to find the bearing seat ground down to a good sliding fit on the bearing inner race to facilitate end float adjustment. Usually this gives no trouble though, as long as there is no perceptible radial play, with the bearing fitted using high-strength Loctite and the cush drive nut done up properly.

As long as there is no relative movement between the inner bearing race and the crank, there is no obvious reason, as to why the shims should fail 

[manosound]

Markus,

For me, your post brings a lot of questions and I often think that whatever malady we are discussing may someday befall me. So, even if BSA500 understands exactly what you've said, please help me with it, a bit.

Am I correct that you are describing something different from the trial-fit disposable bearing I mentioned? By "bearing seat", are you referring to the inside diameter of the inner race? Is Loctite the only hope for a crank that is undersized on the drive side, or is it a case of, "If you have Loctite, why bother with anything more expensive or complicated?"? I was surprised to see this very use in a picture on Loctite's website ( http://useloctite.com/products/index.html ).

Richard L.

[MG]

Hi Rich!
Sorry if I caused you a headache 

With "bearing seat" I was referring to the crankshaft pin itself. Many people simply grind 2-3thou away (during a crank regrind), resulting in a close sliding fit of the bearing inner race on the shaft. Personally I prefer the disposable bearing method, but there is no real downside associated with the before mentioned method, as long as the cush drive nut is tightened properly.

It had been done on my old small journal crank by one of the POs, without causing any problems, and that crank is now running happily in another member's plunger A10 (well, I hope it still is, haven't heard otherwise at least).
As long as there is no perceptible play and the crank pin isn't out of round, which could cause misalignment of the crank, Loctite is more or less unneeded. The inner race is clamped tightly between the distance piece and crank web anyway. Some Loctite will help to keep the bearing in place with the cush drive removed though and might help save the bearing seat in case of the cush nut coming loose. Imho it is best to leave the securing pin on the crank end away and rather hear the loose nut rub against the primary case, which will give you a chance to stop the bike immediately and fix it before the crankpin suffers damage (or use an SRM hex nut instead)!

Once the bearing seat on the crankshaft is damaged by a rotating bearing race (running on a loose cush drive for extended periods), and is out of round or play is evident, it can still be restored by hard-chroming or flame spraying with a subsequent regrind to restore the press fit.

[Goldy]

Even if the crankshaft is worn and the bearing inner ring is loose on the shaft, it still cannot turn because it is locked up with the C spanner nut. So if it has been turning then either the nut was not tight enough, or the nut inner length is wrong of the lobe is slipping.
All the best Goldy

[bsa- bill]

Grind out a bit of the I.D. on the old bearing and use is as the test bearing when coming up with the correct shim thickness.

Good tip that one, will involve a bit of maths if the bearing inners are not quite the same width, I managed to get it right with a bit of addition possibly more good luck than good maths though

[BSA500]

Engine is nearly finished. Had one problem no means to measure the endfloat as I had misplaced my depth micrometer(machined tube fits over crankshaft spindle to measure depth off it) so I used the old fashioned way. Threw all the shims in and removed them until it spun freely. Put in 26 thou locked up,remove 2 thou shim still locked remove 2 thou,perfect so in theory no more than 2 thou clearance. Abit heath robinson but I need her for work this week,fingers crossed :)

[muskrat]

 Sounds like you need to invest in a dial gauge. I'd go mad splitting the cases that many times.
Cheers

[Goldy]

Yes  you can get them for a few pounds on E bay or autojumbles.

[BSA500]

Back on the road again just in time for some very windy/wet weather joy:)

[groily]

'Well done that man'  . . nothing worse than bikes that don't /won't /can't go anywhere. Steady into the breeze - I think you're passing on your near-hurricane to us in France tonight/tomorrow - must be that old Wind of Change blowing across another continent  . . .

[BSA500]

Its started to get gloomy and I am due to leave for home in 50 mins please please stay dry

[beezermacc]

There is a very good method for setting crankshaft endfloat on the Cheshire Branch website 
www.cheshirebsa.co.uk on their tech tips pages. You only need a set of feeler gauges, an L shaped bracket with a threaded hole and away you go. You only need to separate the cases once.
By the way, I'm not too keen on the idea of skimming the crankshaft axle to allow the bearing to fit a bit more easily. In my experience there are quite a few owners who don't tighten up the crank nut enough, consequently the nut comes loose and the bearing spins. If the bearing is still a tight fit it has a chance of staying put until routine maintenance in the primary chaincase brings the problem to light. If you use the correct bearing and a proper bearing puller I don't see a problem. Also, the bearing needs to be tight on assembly to grip the shims, otherwise there is the danger of the shims slipping down onto the axle radius preventing accurate endfloat measurement. I know people have mentioned Loctite etc. but if everything fits the way BSA intended you can spend your Loctite money on something more useful like petrol or beer (but not both!).