One shim left in engine

[goodoldvic]

Hi, I'm looking for opinions and insight. I adjusted the engine bearings in my '29 tudor. I used the tin foil interference method. In doing so I removed all the shims from the rods, and reduced the clearence by sanding the caps on a steel plate with 400 wet or dry. It worked very well and did not take much sanding to get the desired result. All the babbit was uniform grey in color, and no shiney spots. When I did the mains I removed all but one shim which was on the pass side of the rear cap. I did them one at a time and again sanded the caps to get the adjustment result. The main babbit was also uniform grey, no shiney or melted spots. Been four hundred miles since I did the job and the engine is quiet-er, and the rear main leak is much less. The inside of the engine was very clean. Would I be able to adjust them again this way? Is a re-babbit in my not to distant future? Thanx in advance

[wrndln]

I would say that you probably can't readjust the mains on your car without some machine work. Inserted bearing are one option or rebabbitting the engine is another. As a short term fix, you could have a machine shop mill the caps a few thousands, but this would have lasting effects as the caps couldn't be easily restored to the original size if rebabbitting or insert bearings were done later. It seems like machining the engine to use inserts is the wave of the future. I have heard that insert bearing will last much longer than babbitt and don't ever need shimming - a good improvement. Just my thoughts.
Rusty Nelson

[Patrick L.]

I think I would say that a re-babbitt would be in your far-far distant future. Do you have any idea how long ago the bearings were pored,if ever, and re-adjusted ?

[Mikeinnj]

"sanding the caps" is not a good practice. An example of what you accomplish by sanding can be seen if you trace a circle on a piece of paper, than cut the circle in half.

Next overlap the two halves and push them toward each other and what do they become?

No longer a circle but somewhat of an oval, with minimum contact along the babbitt surface allowing more oil to escape. A farmer fix from the days of old.....

[George Miller]

If it is original Babbitt you should be good for 20,000 miles or more if you did it right. if not original babbitt, any ones guess is good.

[MikeK]

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If you keep the dizzy advance lever out of the knock-knock-who's there zone, you're probably good for 20,000+. Even if you run out of shim it isn't a total crime to take a few thou off caps, provided they stay surface-plate flat. Guys who want to sell you a rebuild will thump the green bible and tell you trimming caps is blasphemy. 0.002 off on a surface plate with carbide paper will put off atoning for your transgressions for another 20,000. Heck, guys took 0.025 off with a bench grinder during WWII and the things still ran. As long as the Babbitt isn't crumbling major chunks you're OK.

[MikeK]

Mikeinnj, the same oval thing happens when you pull shims. The only time the hole is round is when the Babbit is bored with all shims in place.

[Mikeinnj]

Originally Posted by MikeK

Mikeinnj, the same oval thing happens when you pull shims. The only time the hole is round is when the Babbit is bored with all shims in place.

Agreed. I was just making a point; ...or a circle. or an oval

[MikeK]

Originally Posted by Mikeinnj

Agreed. I was just making a point; ...or a circle. or an oval

At least you made a point. Some of my posts create a true circle of confusion.

[goodoldvic]

It looks look original babbit, thickness I could see on the cap and block, and the oil relief gullys looked like stock original caps Ive seen. Its got some piston slap in her, but I'll play that fix by ear (haha). Thanx again for the fast and informative replies.

[George Miller]

Originally Posted by Mikeinnj

Agreed. I was just making a point; ...or a circle. or an oval

Inserts are not round either they should not be. Oval lets the oil get in between the bearing and the crank.That makes a hydraulic wedge.

[Joe K]

In my experience with a (ahem) well worn Model A engine, the problem with sanding the caps isn't so much making the hole egg shaped (although that can be a factor) More, the problem is on rods, the crankshaft pins become out of round.

Downward force (the greatest force) always occurs at one point on the pin, making that point "flat" relative to the rest of the pin. In effect, the rod bearings get "egg shaped."

Adjust as I might my (ahem) worn engine, to the point where the rods were literally binding on the crank, I could not eliminate the rod knock.

So I gave up and had everything rebuilt. Back to square one.

Joe K

[Tom Wesenberg]

I don't like to file or sand caps. What are the crank dimensions on the mains?
If your crank is undersized, then another good option is to buy a new counterweighted crankshaft. Then you could add back shims and have the benefit of the counterweights. If your babbit is good this would also save you the cost of a new babbit job.

[wrndln]

You could do what Tom said, but if you could find a regular crank that is less undersized than what you have now, I don't see why that wouldn't work also. New counterbalanced cranks (Burlington crankshafts) are quite pricy at almost a $1000 a pop. An undersized original crank I would think would be relatively cheap, but may need turning to smooth up the journals. Just a thought.
Rusty Nelson

[MikeK]

A replacement crank with larger journals would not work. The babbitt was originally bored/fitted for, and has established a wear pattern for a specific size journal. Larger journals would give you babbitt contact at the cap parting line and not in the center. For once, I'm at a loss for a quick illustration.

[goodoldvic]

Tom, I guess after a crank is ground on the mains the engine builder would pour new bearings for the undersize crank? So I get a stock sized crank add shims then have it line bored to original size? If I got that right, sounds like a plan to ponder

[MikeK]

If you rebore old babbitt for a new larger journal with added shims, you will need 2 X the added shim thickness to get any new machining contact at the bottom of the cap. The bore centerline always remains at the oil pan plane, not the center of the new shim pack. Remember, it is mainly the bottom of the cap that has worn and you are moving it down (further away) with new shims. If you added 0.020" in shims, you would need a new crank at least 0.040 larger to fit a clean re-bore. Adding increasingly thick shim packs adds a whole new dimension of problems.

Don't forget you'll need to redo the rods also if you switch to a larger crank.

[goodoldvic]

Thanx Mikek, I can see what you are saying. The engine sounds pretty good and I'm just gonna run it like I've been. Thanx for all the input.