Engine Bearing Shims

juke joint johnny

juke joint johnny

Well-known member
What was the thickness of the Rod and Main bearing shims on the A& B engines when they were new?

I think we should use that as a guide when pouring new bearings
 
The original engines that I have taken apart have 2 shims on each side that are about.002 each thick---- if the cap has been cut it may need more--- I have checked the rear cap bore to slinger--- too many shims and it will have too much clearance-- leaks--- conversely if the cap has been cut in the past more shims may be needed to prevent rubbing of the slinger
 
What ever they had when new, will not work the way they did. The reason being being is the amount of filing that has been done, on the part lines, that will leave you short, in the amount of shims, needed. We normally use .032.

If you want the exact amount needed, the only way you can do that is set up each cap on the bare block, with bare caps, that is no babbitt, and measure, up, and down, and side ways and make the hole round with shims, until it is. The caps have to be fit to the block, and not rock, at all.

Now you know how many shims it needs, at this point. When you pour the three caps, they will warp some again. So now clean the babbitt, NO part line metal, and Mic from the part line, to the top of the bolt hole in the cap, then level the caps again, and measure the caps a second time, and if what ever difference, say .003, add that figure to your shim pack amount, and you will have the right amount of shims.

Herm.
 
Thanks Herm
Very informative

I asked the question as some engine builders in the UK do not put the shims in just line bore after pouring the mains
I always thought that was a bad idea and now I know why!!
 
Vince's tutorial/discussion on engine main-bearing shims specifically recommends using steel shims...
Do most Model A parts suppliers offer them?
Would one vendor be better than the others?
Thanks, JB
 
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