Babbitt and Shim Question

juke joint johnny

juke joint johnny

Well-known member
A friend is having his B engine rebuilt.
I know that Ford A & B engines were delivered with shims on the Main and Rod bearings when new.
I believe that the shims should be in place when line boring the mains and the rods when you rebuild one of these engines.Correct me if I am wrong.
But I have never seen what the thickness of these shims should be when setting up the line boring .

I ask because in the UK very few British Car engines are set up this way shims are thought of as some sort of Farmer Fix
So this has to be explained to the rebuilder which is why we need the shim thickness.

I realise that if the shims are left out then the bearing material will be very thin , possibly leading to early failure or the Cam & Crank gear mesh not being correct.
I would hate to see my hard working friend Pay out a lot of money for what would seem a poor quality job .
Thanks in advance
John Cochran
 
John, I think somewhere down the road you have absorbed a little bit of bad info from several sources and it has now become worrysome for you. Don't fear as it is all good.

To start with, the original shims were like .004+/- thick steel (I'm too laze to go pull the print to find the exact #) but the reason for this is the original babbitt was reamed and then burnished during the assembly process at the factory. This created a much tighter fit. The issue with using too many shims under the cap is the cap can have a tenancy to 'walk' which prematurely wear the softer metal bearing.

With regard to shims being left out, --or omitted all together, that is actually a good thing and is often done in full-race applications. The babbitt will not be too thin either. The Camshaft-to-Crank gear mesh is actually controlled by finding the centerline of the crank in the block, so the quantity of shims do not affect the gear mesh whatsoever.

Now this is where the controversy begins, ...it is the opinion of many that the reason we see many shims is because the engine builder did not take the time to align-bore the babbitt and then fit the bearings to the cranks journal pin. If they do a poor (quickie) job, then you may only have contact coverage from the 11:00 - 2:00 position and the 4:00 - 8:00 position. therefore that little of surface support of the crank will lead to quick wear, thus resulting in the need to tighten the bearings (remove shims). Naturally the more surface contact you have, the more the crankshaft can be supported which distributes the load. The more area that carries the "load", the less wear you will have. Therefore, the builders that take the time to do the job properly including burnishing bearings can likely put .002" worth of shims under the caps and have their babbitt job last just as long as what a builder that installs .012" worth of shims on a 'quickie' line bore job. If you look at it in that light, yes I can see how some of your friends would view excessive shims as a "Farmer Fix".
 
No. 1. Long after the Model "B" was made, metal shims were offered for the adjustment part. Of all the Model "B" engines we have rebuilt, I have only had two engines that had a mix of steel and Brass shims. Steel does a bearing of any kind, no good at all. Steel shims can turn magnetic and pick up other particle of steel and cast which would other wise flush out the bearing.

When setting shims they have to be right up to the crank, Brass is fine, but a steel shim next to a steel crank is no good at all.


Yes, you can leave the shims out if your going to use inserts, but then you would have to Align Bore the block and caps, as the holes are not round.

As suggested, do not guess at how many shims any one engine is lacking. BE SURE.

Put on the rear main cap and Mic the shell up and down, and then side ways staying off, or just missing the part lines. Subtract the two and that will show how many shims you need in any one bearing.

This is very important on the rear main as that sets the cap so the cap is as close as you can get to close up the oil gap from cap to the crank.

Lastly, Burnishing bearings is 1930's, out dated techology, K.R. Wilson even knew it when building tools for the Model T.

Herm.
 
Do not leave out shims if doing babbit. Removing shims after the engine is worn loose can make an acceptable repair. The center-line for boring (with or without shims) is the bottom face of the block (or connecting rod). If doing inserts, shims are not necessary. Ron W
 
Most babbit/white metal bearing motors had shims in the rod caps and main bearings. When bearings acquire unacceptable clearance, remove a shim, apply engineers blue, reassemble, rotate rod on crank, or crank in mains, split caps, scrape high spots, perfect new bearings.
No mechanic would have simply removed shims, maybe a farmer.
You all got bad memories??!!
 
Thanks everyone for your input !! I do have a better idea how it should be set up now .
40 Years of Model A's and still learning!!!

John Cochran
 
Ok I'm gonna pose this question for Tom Walker & Ron W, in your opinion what causes Babbitt bearings to wear prematurely so as the clearances "unacceptable"?
 
Brent
I didn't say wear was premature, just wear from use. "Unacceptable" as in there is a spec for clearance in your bearing, beyond which you may need to do something about it.
Babbit is super bearing material, soft enough to absorb particles of metal in yr unfiltered oil, and not wear out your crank too fast, but resilient enough to not wear fast with very low/non existent oil pressure!
 
Tom Walker said:
Brent
I didn't say wear was premature, just wear from use. "Unacceptable" as in there is a spec for clearance in your bearing, beyond which you may need to do something about it.

Babbit is super bearing material, soft enough to absorb particles of metal in yr unfiltered oil, and not wear out your crank too fast, but resilient enough to not wear fast with very low/non existent oil pressure!
Click to expand...


OK, that is a fair statement, ...so how long (how many miles) does shimmed "super bearing material" go before it needs to be re-shimmed, --and why is that??

.
 
There is no way anyone can tell how long a de-shim job will last. It depends on oil, owner, and quality of the engine rebuild at the time.

One thing for sure, when a New Babbitt job is align bored, what ever size the shim packs are when starting the align Bore, there should be the same amount of shims as when the crank is set!

You do not remove shims to set a New crank, just because you missed the Bore size!

On a splash engine, after removing .006, that is the turning point, no matter even if you started with .032 thousandths total. After that your bearing adjustment is all cobble.

On a pressure engine, by removing .002, after that it will show small to great signs of burning oil!

Herm.
 
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Kohnke Rebabbitting said:
No. 1. Long after the Model "B" was made, metal shims were offered for the adjustment part. Of all the Model "B" engines we have rebuilt, I have only had two engines that had a mix of steel and Brass shims. Steel does a bearing of any kind, no good at all. Steel shims can turn magnetic and pick up other particle of steel and cast which would other wise flush out the bearing.

When setting shims they have to be right up to the crank, Brass is fine, but a steel shim next to a steel crank is no good at all.
Click to expand...

I honestly do not know where this 'stuff' comes from. :o It is hard enough for folks here to understand the facts much less disproving other's myths & misinformation. Same applies for burnishing when it is clearly described on the print!!

.
 

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Well I guess I may be the first to find out how long a engine will go with no shims. Haha. When going thru mine, I did order a pack of shims in case I needed them. After using plastiguage, it showed only one connecting rod needed shims but none for the mains. So, hope I'm good for a while. I also have 2 complete spare engines in case something were to fail or my rebuilding abilities were not spot on. Just in case.
 
Barber31 said:
Well I guess I may be the first to find out how long a engine will go with no shims. Haha. When going thru mine, I did order a pack of shims in case I needed them. After using plastiguage, it showed only one connecting rod needed shims but none for the mains. So, hope I'm good for a while. I also have 2 complete spare engines in case something were to fail or my rebuilding abilities were not spot on. Just in case.
Click to expand...





You needed to add shims ?!
 
Yes, on one connecting rod. It was way too tight. It would actually bind up the crank. The other rods and mains did not need shims. They were within tolerance.
 
Reading the above posts, there seems to be a deal of over-thinking going on. . You could re- babbit a motor without shims. You would simply then have no chance for re-setting the bearing clearance when they wear. When you have your main and big end bearings re-babbited, your chosen bearing man could install shims if you ask him to. . He would do this before boring the bearings.
If the boring is done incorrectly, the clearance will be either too big or too small. It is either right or wrong. Shims are not there to correct bad machining!
Its really not that complicated.
 
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I had a B block re-babbited specifically for a full pressure conversion. When discussing the job with the machinist, he pointed out that we could not use shims because they allow the oil under pressure in the bearing to leak, which defeats the object of pressurising the system. I have run this engine for 5years with half a dozen track races a year each year, and road miles in between, and it still holds 50 pounds pressure with hot oil.
Splash system is not affected in this way by shims.
 
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