A10 crankshaft shims, problem

[Wakeman]

I have had an A10 Golden Flash for about 50 years. I don't ride it too much anymore, but I do still ride it. I have had to remove and rebuild the engine several times because the crankshaft shims get eaten up. After about 4,000 miles I start finding pieces stuck to the drain plug magnet (SRM type cast aluminum sump plate) I thought I had licked the problem last time by using loc-tite on the shims to secure them to the center hub of the main roller bearing. Does anyone else have this problem? any suggestions?

[idie]

I would think that the shims are not being held tight enough by the bearing, so with end float the crank movement is chewing them up. Maybe the bearing is loose on the drive shaft.

[Wakeman]

Thanks for the fast response. I carefully measure the end play and try to leave .001 to .002 clearance. I do this with a main bearing that fits snugly to the crank. When I'm satisfied that the clearance is right I use red loc-tite on the bearing where it fits to the crankshaft. Red loc-tite assures a "permanent" fit. It can only be removed by heating the bearing and shaft to soften the loc-tite. I've built many A10 engines and this is the only one that gives me a problem. I built the engine completely stock, flat top pistons, original cam, original 376 Amal carb, etc. Unfortunately, I can never find one shim to get the right clearance, so I have to use two. That's why I loc-tite them together, so they won't spin with respect to each other.

[DAVE BRADY]

Hi,

If one shim cannot be found then what about making one. There is a wide range of shim stock so the correct thickness should be out there.

Dave.

[Wakeman]

Thanks Dave,
It has occurred to me. I'll try that on the next go-round

[EDDIE SIMPSON]

the problem with shims being spat out especially thin ones is an old problem but little heard of now as people dont do high milages on a10 s like they used to. one method is to make a shim to go between the outer ring of the roller bearing inside the crankcase bearing housing. as they are not moving parts the shim will stay in place.

[Spaceman]

Ironically, it is possible that the use of Red Loctite is partially the cause of the problems on this A10!

The way the A10 is designed to work is that the crankshaft is supposed to be clamped against the drive side roller bearing inner race by the pressure from the cush spring. In so doing, the drive side shim(s) should be tightly sandwiched between the inner race and the crankshaft web.

If the cush spring is too weak or the bearing inner race has been glued to the crankshaft then, when the engine heats up, the shim or shims may no longer be held tightly in position. They could then end up being free to rotate on the crankshaft and, in so doing, suffer wear against the inner race or the crankshaft web until they eventually fail.

I understand why Red Loctite has been used but, unfortunately, it will then not allow the cush spring to do its job in terms of clamping the shim(s) and stopping them from rotating. As said, there have been other cases where the drive side shims have failed but this may have been down to a weak cush spring. In this case, it is almost certainly the Red Loctite that has contributed to the problem.

[DAVE BRADY]

Hi,

A weak crank spring could well be part of the problem but I have had shims come out even with a good spring.  I suspect that if the bearing is not a good fit then that will also contribute tom the problem.
BSA used a shim cup on A65s so perhaps this was design problem.

Dave.

[Spaceman]

I guess the design relies on the tightness of the fit of the crankshaft within the roller inner race - if it is too tight, the spring may not be strong enough to pull the crankshaft through to clamp the shim(s).

I had a think about the A65 shim cup and the only reason I could think of for it being there was to contain the shims if they started to break up. Maybe that was a result of experience with the A10?

[JulianS]

My view is that the most important thing is that the inner race of the roller bearing is a good drive fit on the crankshaft so it will not move when in place. That is what makes setting the end float so hard - the difficulty in removing the inner race to adjust the shimming.

[Bess]

Hi,
    If the end float is .001/.002" under spring pressure the bearing probably wont move laterally and damage the shims, its the momentary turning of the inner race that tears thin shims. An indication would be polishing of the crankshaft under the inner race.

As others have said, its best to use 1 correctly sized shim and ensure the inner race is an interference fit on the crankshaft (many are now a loose interference or light fit). A loctite product under the inner race if the crankshaft wear isn't to great would be okay. Worth giving SRM a call, they will let you know which loctite spec. they use. If the wear is too great they can rectify at a cost.

Best wishes...

[Mike Farmer]

 

Interesting. The way I see this is that if the crankshaft is snubbed up tight to the inner bearing race and held in place by the spring its not actually end float, and the shims should not be able to rotate seperate from the bearing. Instead of using locktite to hold them together it might be better to use it to bind them to the crank or to the inner bearing spool.

Long time since I did one of these engines so dont really know.

This maybe of some interest. On a recent A65 with the bearing cup in place the bottom jammed up solid. It appears to have been a mismatch between the crank and cases. Got around it by machining about .003 off the timing side web of the crank. Ensuring that the conrods still ran at 90* to the crank. What the long term effect will be is unknown.

Mike

[Wakeman]

Thanks for all the thoughts and comments. I'm looking them over carefully. It's been about 5 years since my last rebuild so it's hard to remember exactly what I did. I did make notes and have attached one (1992!). Also, the page from the Service Sheets.
At 73 I'm not looking forward to removing the engine again! However, I am saving all of your comments and when I do, I'll study them. I remember that the A65's had a shim cup, so that was probably to alleviate the problem.
I'm very appreciative of your time and comments
Greg, Virginia, USA

[Wakeman]

That sketch is from my 1963 Super Rocket which I still have and ride, but I've only done about 6,000 miles on it. I also have a 1956 Road Rocket. I have notebooks of sketches!