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#831524 11/30/20 3:09 am
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Hey all,
On my 64 thunderbolt motor I'm about to start assembling, the parts diagram shows a shim cup, part 68-0168, that looks like it goes between the crank and whatever shim/shims needed for end float then crank bearing then inserted into case. Is this correct? I don't have a shim cup in my pile of parts. There's someone that has the part listed on eBay and the picture looks to me like the lip of the shim cup would hit/rub on the bearing - protruding past the actual shim.
Am I painting a clear picture?
Am I missing something?
The shim cup rides against the crank...?
Doesn't seem correct...
Thanks.

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Presumably this is a roller bearing drive side? Crankshaft web - shim cup - shims - bearing
Shim cup rim is larger than the bearing inner race O.D.

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If your fear is that the shim cup lip edge will touch the bearing balls, then don't worry about it. It's not going to.

The shim cup may differ from OEM, though. Early ball bearings had a smaller inner portion. Then, the roller was introduce with its own shim cut, and later ball bearings use this size as well. So you may have to mix and match.

Keep in mind that, with a ball bearing, you're setting running clearance instead of endplay. Once you tighten it all up, it won't move like a roller bearing does.

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Originally Posted by DMadigan
Presumably this is a roller bearing drive side? Crankshaft web - shim cup - shims - bearing
Shim cup rim is larger than the bearing inner race O.D.
Thank you for the affirmation!

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Originally Posted by MarcB
If your fear is that the shim cup lip edge will touch the bearing balls, then don't worry about it. It's not going to.

The shim cup may differ from OEM, though. Early ball bearings had a smaller inner portion. Then, the roller was introduce with its own shim cut, and later ball bearings use this size as well. So you may have to mix and match.

Keep in mind that, with a ball bearing, you're setting running clearance instead of endplay. Once you tighten it all up, it won't move like a roller bearing does.

Cool. Hopefully the new bearing fits with the shim cup I'm purchasing off eBay!
I've rebuilt a later (68) so am familiar with the end play setup. How do you set running clearance on the earlier ball bearing setup?

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On the ball race setup, the bearing retains the crank so fixes the end float.
In that case you should pay attention to centring the crank in the cases.
It's one of the reasons a lot of blokes just use the ball race in late engines.

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Originally Posted by NickL
On the ball race setup, the bearing retains the crank so fixes the end float.
In that case you should pay attention to centring the crank in the cases.
It's one of the reasons a lot of blokes just use the ball race in late engines.


So the bearing is pressed into the case and the crank is pressed into the bearing and the shims just center the crank?

Sorry, feeling dense here..

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I went with the roller bearing. I had 2 shim cups, and early and a late version. As I recall neither fit my KLH bearing.
I ended up buying shims from McMaster Carr that were a close fit to the crank size. No shim cup.
Then discovered the fillet on the crank so had to enlarge the ID of the shims. As I recall...


1966 BSA Lightning
(2) 1967 Triumph "Choppa"s
1974 Indian ME125
1960 Harley Servi-Car
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The bearing is a sliding fit on the crank and is of course retained by the sprocket etc assembly
The bearing should be an interference fit in the case, warm up the cases in an oven to around 100c
or boil them until done,,,,,,the bearing should drop in.
If you have a friend with a lathe, get him to part you off a spacer, once you've measured the end float,
that way you don't need to mess about with shims and the cup. Aim for a thou or two end float, you'll
have to clock the assembled cases with the crank fitted to figure out the size.

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Originally Posted by drunkenmonkz
Cool. Hopefully the new bearing fits with the shim cup I'm purchasing off eBay!
I've rebuilt a later (68) so am familiar with the end play setup. How do you set running clearance on the earlier ball bearing setup?

"Running clearance" simply means that there will be enough space in the case to spin the crank freely once warmed up. The goal here is to ensure there is some space on the right side of the crank, between it and the lip on the timing-side bush.

It doesn't have to be much, probably .003" (about the same as the endplay set with the roller bearing). With the cases bolted together, I aim for no rubbing when installed dry. Obviously, this is from experience so may require a number of test fits to get it right. You need to "hear" with your hands as much as with your ears. Installing the sprocket, rotor, and nut will only increase this space so I've found this to be a good setup.

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Be worth adding that if your using a ball race you do the check without the mentioned sprocket/rotor etc fitted otherwise you won’t be able to feel the end play.

If your using a roller, fit the sprocket etc and tighten it up that way you will be feeling all available end float


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

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i an a bit confused in this thread where several posters have used the term "end float" whist talking about a ball brg motor .........there is none when everything is locked up (ie the crank cant float ) sure there is some end float BEFORE sprocket etc is tightened up but none when it is

perhaps they mean working clearance between TS main bush and crank to accommodate a minimal amount of expansion ?this working clearance does not mean the crank floats side to side a few thou as do the roller engine , which is what they have a bronze faced spacer The pre 66 doesn't even have a trust washer/spacer there as do the post 66 roller set ups

In any case if you are talking about using a shim stack and cup on a pre 66 a65 to center the rods with the bore i would go for a solid one piece washer every time since that washer is locked in place by the bearing inner race so it doesnt even matter what its made of ........just not bamboo though ok

i fear we may be confusing OP with in correct technical terms

there is a really minimal amount of float (more correctly clearance) (microns) within the brg itself but i dont want to start a discussion on CN C1 C3 bearing grades we dont want the op pulling his hair out


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Good info. So how do I know what size shim to use? I've got three .010 .005 and .003. as well as the shim cup coming in the mail. If the bearing locks the crank in place then the shims are only to center the crank? How do I know it's truly "centered?

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If you get the clearance on the right side of the crank within a few thousanths, the crank will be close enough to centered. The conrod big ends can slide back and forth on the journals some, so a thousandth or two one way or the other will not make a difference.


Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
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A lot, probably most of the engines i've built have been a mixture of parts.
IE, early cranks into later cases etc etc. The only correct way of doing the
job is to measure it. It's close enough to use the flywheel as the guide, just
measure the width and halve it, mark a line around it, then put a piece of
shim into the joint faces of the cases and line that up.with the mark. That
will then allow you to move the crank back and forth with a clock on one end.
Thus establishing the shim size.

It's not that critical but makes for a sweeter engine if all is lined up. Doing the
job with mixed parts can be a little more complicated. With the later cranks
and roller setup you have to setup for minimal end float or make up TS thrust
washers etc. If all your parts line up with the book, just follow the instructions there.

Last edited by NickL; 12/06/20 11:29 pm.
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Originally Posted by NickL
A lot, probably most of the engines i've built have been a mixture of parts.
IE, early cranks into later cases etc etc. The only correct way of doing the
job is to measure it. It's close enough to use the flywheel as the guide, just
measure the width and halve it, mark a line around it, then put a piece of
shim into the joint faces of the cases and line that up.with the mark. That
will then allow you to move the crank back and forth with a clock on one end.
Thus establishing the shim size.

It's not that critical but makes for a sweeter engine if all is lined up. Doing the
job with mixed parts can be a little more complicated. With the later cranks
and roller setup you have to setup for minimal end float or make up TS thrust
washers etc. If all your parts line up with the book, just follow the instructions there.

The crank and cases are from the same motor. Connecting rods are new cromoly from map cycles, srm oil pump and newby clutch/belt drive. The head and cylinders are from other years/models. The cylinders I'm using were in better shape than the ones original to the motor and I'm putting a thunderbolt head on instead of the lightning. all those things shouldn't be an issue now though (I'm sure will be later...)
I rebuilt the 68 motor in my bike now almost ten years ago and it ran solid for many thousand miles (until return oil line popped off on my way to work this spring)
I may seem dense and repetitive in my questions, sorry for that, I just want to make sure this motor will be as solid as an a65 can be. And that I'm understanding things absolutely correct.
all the tips, tricks and ideas for building it are greatly appreciated!!!

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Sounds like you've got all the right pieces for a dependable bike.
If you don't mind, what type of plain bearing do you have and how did you handle the line bore?


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1974 Indian ME125
1960 Harley Servi-Car
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Rhp c3 main bearing. Seemed like the best option. That I know of anyways. Something better in your opinion? Also a friend of mine is a fantastic machinist so we bolted the cases together, had them blocked on the mill bed, trammed in the head to be inline with the cases, removed the left side case then bored the bush to fit the crank. I think we got it to .0005 or .0008 or something like that. I can't remember what the tolerance call out was but it was as close as we could get.

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Is .0005-.0008 the tolerance or the clearance? The clearance should be min. .0015".


Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.

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