Babbit process question

Dick Steinkamp

Dick Steinkamp

Well-known member
I picked up what was described as "a good used motor" but with no history. I've taken it apart down to the long block to inspect it and fix any thing that needs fixing prior to putting it into service.

The babbitt was somewhat of a mystery to me. Under each rod and main bolt was a single .035 shim (yes, .035). The babbitt looked very good with little wear. The rods plastigauged at .003 and the mains at .002 with the single shims in place.

I plan to use some new shim packs and get the clearances closer to .001-.0015, but why the single .035 shims?

My THEORY is that in the babbitt pouring and finishing process, the rods and mains are assembled with the single shims, then line bored to the crank dimension plus the desired clearance. The motor is then assembled with the shims used in this process. Is this close?
 
Dick,

You are correct about the main and rod caps being bored and fitted with the shims installed. From this point on, the shims stayed with each bearing cap, on their fitted location.

OEM shims came as a "pack", laminated layers that were carefully peeled-apart with a sharp knife when it came time to take-up for wear.

Are you certain you're looking at a solid shim, and not a tightly packed stack ?

( Try dragging a knife across an outside corner of the shims, to see if anything separates.)
 
Shims may appear solid but are not. Separating is a bit of an aquired skill. Shims are enexpensive from our good suppliers. You might want to buy a set to practice on.
Hugh
 
Many engines were done with a single thick shim. I like them. I find it a PITA to separate shim packs. I just measure the shim and sand it on a sheet of glass to the thickness I want. I measure 3 places across the shim to make sure I sanded it even, install it and make sure the clearance is correct. This makes it easy to have both shims the same thickness [ I know its not supposedly necessary].
I like .0015" on all and maybe a little tighter on the rear main.
I just figure if I'm going to do it I'll take my time as I'm no longer in any hurry to do anything and make sure they are set where I want them. Do it once right and it'll probably never have to be done again in our lifetime.
 
Thanks, Patrick. I'm pretty sure these are a single, thick shims, but I'll report back if I find different. I like your sanding idea. I think the shim packs contain .002 shims so it would be tough to get them where I would like to get them without having to resort to a different amount of shims under each side of the same bearing cap.
 
Dick Steinkamp said:
Thanks, Patrick. I'm pretty sure these are a single, thick shims, but I'll report back if I find different. I like your sanding idea. I think the shim packs contain .002 shims so it would be tough to get them where I would like to get them without having to resort to a different amount of shims under each side of the same bearing cap.
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Even with a shim pack if I get frustrated trying to separate them, I just sand them too. Some will come apart, some can be stubborn.
 
For many years, the standard shim pack supplied for the engine rebuilding trade by Federal Mogul was labeled "1/32 inch" on the package, which is close to what you report. If you are already close to the desired clearance, I prefer to sand them to fit.
 
Dick Steinkamp said:
I picked up what was described as "a good used motor" but with no history. I've taken it apart down to the long block to inspect it and fix any thing that needs fixing prior to putting it into service.

The babbitt was somewhat of a mystery to me. Under each rod and main bolt was a single .035 shim (yes, .035). The babbitt looked very good with little wear. The rods plastigauged at .003 and the mains at .002 with the single shims in place.

I plan to use some new shim packs and get the clearances closer to .001-.0015, but why the single .035 shims?

My THEORY is that in the babbitt pouring and finishing process, the rods and mains are assembled with the single shims, then line bored to the crank dimension plus the desired clearance. The motor is then assembled with the shims used in this process. Is this close?
Click to expand...

All shims are easy to get apart. Take a snout nose pliers and hold one end of the shim about 3/4 in from the end. Hold the shim pack in a little torch flame and the glue where the pliers does not touch will burn away. Let cool and the shims will come apart easy.

Dick, what kind of motor do you have?

What is the rods forging number, on the rods?

Herm.
 
Herm,
It's a Model A engine. 2695495 (December 6, 1929). It has 60 over pistons in it. I looked for a forging number on the rods, but I can't find one. The long block is still assembled. Where would the forging number be?

The #4 rod has a small #3 stamped on the big end. No other rods are numbered. My guess is that at least this rod was replaced during one of the rebuilds of the engine.

I was wrong. The shims can be separated. I worked an edge with a razor blade and can make it happen. I still think I'll try Patrick's idea of sanding them. It actually sounds easier and more precise.
 
A box knife or exacto knife is a good tool to separate shim layers with. Laminated shims were actually soldered together many years ago. In recent times they are laminated using fiberglass resin.
A sharp knife blade works on either kind. I would rather peel an extra layer off of one side to get the needed clearance rather than sanding a shim by hand.
 
Shimming the main bearings has been a challenging experience for me. One of those things the sounds easy but isn't. It took along time on my first engine repair and I could only seem to get the clearances to .0015" to .002". I'm running this engine currently with no problems.

Working on a counterbalanced diamond block engine using vintage parts. I've finally succeeded getting all three mains .001". The breakthrough ,for me anyway, was making my own shims to get that last .001". Anyone that has tried to separate a shim stack will understand. I bought an assortment of 6"x12" brass sheets ranging from .001" to .015". I had the center main at .001" but the rear was either too tight or too loose. I ended up using a .0015" homemade shim in the stack to get the .001" bearing clearance. .001 & .0015 is thin enough to cut with Exacto blades.
Hugh
 

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Hugh, .001 is to tight for a 1.875 main.

The minimum should be .001-80, to plus .002-30.

Or you take a big chance of slipping the first .010 of the bearing surface, and filling the oil grooves, and those hardened particles going back through the bearing.

Herm.
 
Kohnke Rebabbitting said:
Hugh, .001 is to tight for a 1.875 main.

The minimum should be .001-80, to plus .002-30.

Or you take a big chance of slipping the first .010 of the bearing surface, and filling the oil grooves, and those hardened particles going back through the bearing.

Herm.
Click to expand...

Herm,
I'm a rookie. What do you mean by .001-80, to plus .002-30.?

What are you recommending for rod bearing clearances?
 
Dick Steinkamp said:
Herm,
I'm a rookie. What do you mean by .001-80, to plus .002-30.?

What are you recommending for rod bearing clearances?
Click to expand...

That would be 1 thousandths and 8 -1/10's of a thousandths, To 2 thousandths and 3- 1/10's of a thousandths.

What it amounts to is .001 thousandths per inch of crank size Minimum, and plus a 1/2 thousandths Maximum.

A "B" crank is 2" on the mains, for this purpose, so clearance would be .002, Minimum, and .002-50 Minimum.

The "B" rods are 1.875, so Minimum clearance would .001-90, to plus a 1/2 thousandths, which would make it .002-40 Maximum.

An "A" crank is 1" and 5/8, or 1.625 on the mains, So the Minimum clearance would be.001-60, and the maximum would be, Plus 1/2 thousandths would be .002-10.

The rods are 1.500, so clearance would be .001-50, Minimum, or plus a 1/2 which would be .002.

Herm.

That brings me to shims. It is easy to use shims. They should be in .002 thousandths pieces, the cheap ones are in .003 thousandths pieces.

If you say pull a .002, and it is now to tight, and with the .002 it is to loose, put in .001 thousandths on the side you took the .002 off of, as that lets it down by a 1/2 thousandths.

Herm.
 
Herm,
Thanks for the explanation. I was going off the red book. Figured.001 - .0015 meant .001 was the dimension to go to. My engine is still on the stand with the pan off so I can add .001 to one side easily.
Thanks,
Hugh
 
Herm -

If we wind-up with an un-equal stack of shims between both sides, is there a preference as to which side has the thicker stack ?

I seem to remember something about babbit Chevys favoring the thicker stack on the cam-side of the bearing ?
 
Kohnke Rebabbitting said:
That brings me to shims. It is easy to use shims. They should be in .002 thousandths pieces, the cheap ones are in .003 thousandths pieces.

If you say pull a .002, and it is now to tight, and with the .002 it is to loose, put in .001 thousandths on the side you took the .002 off of, as that lets it down by a 1/2 thousandths.
Click to expand...

Thanks, Herm!

On the shims...where do you get the .001 shims or do you have to make them?
 
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