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So I was checking the dynamic timing using my disc screwed into the left-end of the crankshaft, and a strobe light.
That was all OK but when opening/closing the throttle I could see the disc moving. Having measured it, I seem to have about 0.5mm endfloat.

I'm going to to have to pull it apart, but any theories on where this could have appeared from? It's done about 3000 miles with my original crank built up by Nigel around an Alpha big end. All new bearings throughout. When I built it, it was all shimmed up to virtually zero endfloat, but free to turn. I seem to remember assembling and splitting the cases 6 or 7 times to get it right.

Ian

If you originally set it up with what appeared to be zero endfloat its just possible?? that the endfloat was in the negative range (this will still allow the crank to spin quite freely) and then in service one or the other or both main bearings will start to prematurely wear = unexpected endfloat, also when you were measuring the original endfloat where you bolting up the cases with the gasket you were going to ultimately use and bolting up to full torque each time? (I grease the gasket so it won't stick).
Cheers,
George

Hi Ian

did you radius the shims or make a radius with a old mainbearing ?

Eldert

Eldert wrote:Hi Ian

did you radius the shims or make a radius with a old mainbearing ?

Eldert

Eldert - can you explain that a bit more for me please? But I think the answer is going to be "no"....

blethermaskite wrote:If you originally set it up with what appeared to be zero endfloat its just possible?? that the endfloat was in the negative range (this will still allow the crank to spin quite freely) and then in service one or the other or both main bearings will start to prematurely wear = unexpected endfloat, also when you were measuring the original endfloat where you bolting up the cases with the gasket you were going to ultimately use and bolting up to full torque each time? (I grease the gasket so it won't stick).
Cheers,
George

Yes, the gasket was in place when checking the endfloat.

Aye Ian,

Not too steal Eldert's thunder, but have a look at some of the links from this DuckDuckGo search.

radiusing_steel_shims

I think you will read what he is talking about. If my assumption is incorrect, my apologies to you both.

Good health, Bill

Ian

Almost certainly as Eldert said. The cranks have a large radius where the shims sit and care should be taken that the shims are sitting against the face and not on the radius. This is done by chamfering/radiusing the thickest shim and placing it against the crank face. If this is not done, in use the shims will wear and distort and end clearance will appear. Other reasons for picking up side play could be a poorly seated bearing (unlikely) or a failing bearing. Either way give the bevels a good looking at as side play can give the teeth a hard time. Give me a call if you need a better explanation.

Nigel

LaceyDucati wrote:Ian

Almost certainly as Eldert said. The cranks have a large radius where the shims sit and care should be taken that the shims are sitting against the face and not on the radius. This is done by chamfering/radiusing the thickest shim and placing it against the crank face. If this is not done, in use the shims will wear and distort and end clearance will appear. Other reasons for picking up side play could be a poorly seated bearing (unlikely) or a failing bearing. Either way give the bevels a good looking at as side play can give the teeth a hard time. Give me a call if you need a better explanation.

Nigel

Thanks Nigel - I understand what you (and Eldert) mean. Looking at my photos, I can just about see the radius on the crank although it looks pretty small. I didn't appreciate that particular subtlety when I put it together!
I'll check what shims I have left and will need to order some gaskets in due course I guess.
It's a pity to pull it apart as it's running pretty well otherwise, and is oil-tight too.

A bit of free time today so I’ve started pulling it apart.
All the ancillary parts are off and everything is disconnected so next session will have the motor out.

Slow progress due to Stafford Show last weekend but got the motor out yesterday and starting pulling it apart.
The bottom bevel gears themselves look OK, but the key for the gear on the crankshaft is rather worn-looking.
I don't know if it's because the nut has lost clamp onto the gear due to the crankshaft endfloat, but the key looks to have been rocking in the slot.

There is also some vertical play in the assembly of the gear that meshes with this one. I don't have any obvious explanation for why this has developed, but I haven't taken it out of the crankcase yet.