VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 Main Bearings Purchase?

Hello All,

I need to buy a .010 undersize rear main bearing for my 38 Chevy original 216. I am not sure if I can get a single bearing (just #4), or I have to buy a whole set of 4 bearings?

Does anyone know the best place to buy them?

I am looking at Chevs of 40's and Kanter, (but I think they only sell the whole set) ??

Thanks for the help.

Mike

Do I need to install my main bearing caps with shims or do I install the new main bearings w/o shims? [I am talking mains and not rods]

Mike

The '38 216" engine originally had poured babitted main bearings, not inserts. If the engine was converted before you owned it, contact an engine builder and see what he can come up with. If you had it converted, check with whoever you had do the machine work. I've never seen bearings offered as a partial set, always as a complete set.

An engine with insert bearings should not have shims installed.

I think that Bowtie Bob is a bit confused. Originally the main bearings are indeed inserts but not precision. What that means is that the bearing shells are meant to be line bored to make sure they are the right size and properly lined with the crankshaft. Later when more precise machinery and techniques were available precision bearings were produced. They did not need to be line bored but as is the case with race engines today line boring is still the most accurate method to insure correct bearing sizing and alignment.

All bearings even those produced today have some babbitt on the bearing surface. It is very thin on modern bearings and thicker on older ones.

I bought my 38 main bearing inserts from Chev's of 40's though they source from EGGE. They only sell full sets. Occasionally I see part sets on Ebay but then you're dealing with inaccurate labelling, damaged parts, unknown handling, wrong sizes, etc. I'd be tempted to buy a full new shiny set.

The third main insert needs to be machined to provide the proper crank thrust clearance. Each set of inserts required shims. The new inserts were machined to provide 10 thou WITH the shim packs in place so you will need shims.

The shims were hard to find for 37-39. They are readily available for the later main caps but not 37-39. I bought them from Northern Auto Parts: 801 Lewis Blvd, Sioux City, IA 51105 800-831-0884

Forgot to mention: Both Egge and Chev of 40's looked at me like I had 3 eyes when I asked them whether their sizing was with or without shims. Chevs of 40's assumed no shims should be necesary so sent me a second set when the first was undersized. 2nd set was the same as the first and a shim pack brought them to exactly 10 thou over.

OK,

I understand that the origianl bearing was a "shell" bearing that was line bored. It could be removed and replaced since it was a "shell" or what we call an insert, but was not finished to final size, hence the need for line boring to get it to correct size and alignment.

That be as it is, I understood there were brass shims placed between the block and the cap as the cap is bolted up. These could then be removed as needed to take up a small amount for wear on both the babbit of the bearing and the steel of the crank (hopefully mostly on the bearing).

When I install the new precision bearing, will its outside diameter be the same as the opening of the cap and block with or without the brass shims?

I understand when the rods are converted (which I am planning to do) the shims are removed, the cap is replaced on the rod and the new opening is bored so the shims will not be involved in the new rod bearing. I understand that is how the rods are done. I am asking about the main bearings since I wonder if I should get new brass shims and what is the total thickness of the brass shims packet for each bearing?

I called Chevys of the 40's and they told me $135 + $15 shipping and that they did not come with shims. I called Kanter and they told me $185 + $28 shipping but they come with shims. Based on that it seems the shims are necessary?
Mike

I think that shims are only necessary if the company that rebabbits the inserts sizes the bearings for them. I know many of those that repour rods do not set them up for shims but, I always ask that they do and supply the shims to be used.

if you are using the ORIGINAL line bored main bearings you can not replace just one insert - with a non-precision bearing or a precision bearing. If the original bearings have been replaced with precision bearings one or more new precision bearings can be replaced.
Chevrolet 6 Cyl engines from 1929 through 1947 used "rough" main bearings. If they were replaced actually all four would need to be replaced and the line bored to insure that all were at the same "level". Now if you install say just one bearing, even a precision bearing, it may be thicker or thinner between the crank and the block and impossible to adjust.
In 1948 Chevrolet used precision main bearings in production. At that time they discontinued the "rough" bearings for the 1929-47 engines and sold just the precision type. On the initial installation all four precision bearings had to be installed. From then on just one bearing could be installed.
A .010" under sized bearing could now be installed (of the precision type) for just one location BUT the crankshaft would then have to be turned to that undersize.
All bearing manufactors changed to the precision bearings also for use on the pre1948 engines.
When you purchased a new main bearing "insert" or connecting rod it came with a pack os shims. A new engine came with properly adjusted bearings and the same number of shims. Usually had 4 .001" silver shims and 4 .002" copper shims. The shims would then be removed later after the bearing babbit or the crankshaft journal wore slightly.
Yes you will need to use shims to properly adjust the bearings, even if they are new. That was always the advantage of the old 6 Cyl engine. As long as there was babbit material left the bearings could be "snugged up".