VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 Bearing Shims in a 1941 Chevy 216

Should an engine that's been line-bored and converted to insert rod bearings still need shims on both the mains and the rods? Looks like if the crank has been turned to 0.010 and the bearings are 0.010, shims should not be needed?

Thoughts?

I think the rod conversion eliminates the need for shims.

Chevrolet changed to precision main bearing inserts in 1948 and they still had shims. The 235 continued to have main bearing shims up till mid 1955 when they changed from the dowel retained inserts to the tang type. The inserts than could be replaced without removing the crankshaft.
Chevrolets with innsert rods did not have shims. I guess it would depend on ow the rebuilder set the engine up. I my self would prefer at least main bearing shims.

At the very least, with insert bearings, I would plastigage the bearings to verify how much clearance there is.

That's certainly a good place to start...Any special reason you've decided to take a look/see...?

I'm building a new motor that is all supposed to be machined properly. However, the main bearings are too tight. I can't even turn the motor. I put one set of shims in and nothing changed. It looks like I'm going to be headed back to the machine shop for more work which sucks. A good shop turned the crank to 0.010" and I ordered bearings from Chevy's of the 40s who said that they were out of the parts but would have a machine shop make them for me. So now, I'm left with a motor that won't turn. Who's in the wrong....my shop that turned the crank or Chev's of the 40s shop that made the bearings? Unless I install lots of shims, I think I'm just out of luck. I would have thought a newly machined product wouldn't need a mountain of shims.

I would hazard a guess that neither of them is in the wrong. I would add shims at 0.002" each up to 0.010" on each side. Originally the main bearings were shimmed so the engine could be refreshed under a shade tree if necessary. I just may be that everyone did what they were supposed to do.

The genuine Chevrolet inserts required 4 shims on easch side. 2 .001" and 2 .002". If I remember correctly the shims came in the bearing insert box. That also is the shim count that came in a new engine.

But what about the genuine shade tree machine shop bearings? Shims no longer come with a bearing set nor do they come with an engine gasket set. I know they can be purchased seperately. However, I'm dealing with a new setup including insert bearings for the rods and all. I'm headed back to the machine shop to get touched up whatever needs to be touched up.

I have used the genuine Chevrolet shop manual procedure for setting the correct number of shims on my 1940 Main Bearing Caps. The crankshaft was turned .010" and the main caps have a max of 1 - ,002" shim on each side of the 4 main bearings. The front main bearing has zero shims. The crankshaft will turn with only a minimal amount of hand pressure. It appears to match the language in the 1940 shop manual.
Question? What level of clearance does this give a 1940 Chevrolet engine when I am all done? Did Chevy end up with between .001" and .002" on the mains?

dtm

That would be the ideal bearing clearance....with the rods kept at .001".............

Dave aka Toolman

My 1942 "Motor's manual sez rods .0015 - 0025, mains .002 - .004.

Chevrolet says .001" to .003" on the mains. At .003" the rods will be making noise as soon as the high spots wear off and the babbitt compresses.
I always do the rods with the tapping back and forth method as per the shop manual and have had good results. If that is followed the rods will be at .001".

If it is of interest, when putting together my 216, I shimmed the rods without the pistons attached and was able to feel the drag quite easily.

I also use the tapping back and forth method on the connecting rods. Since my mains are done, I am currently looking for a local machine shop to machine my rods over to accept insert bearings. I am checking with one this Friday. You would think that we all would know what model/brand of insert rod bearings would fit properly. Chevrolet used the same rod from 1937-1947.

dtm

Dave

I have inserts in my '40. PN is FM (Federal Mogul) 1415 .0010 undersize. Check NAPA online. I think they use the same part number with their prefix. I had my inserts when the rods were machined so did not have to use shims. 'course you have to be careful and keep the inserts with the rod and throw it was machined with. No matter how good the machinist is there are slight differences in the rods and crank throws. My rod clearances are all between .001 and .0015 (plastigage).

I used .001 inserts and shimmed to fit. Each rod took one .001 on one side. However for one rod, I went to a .002 insert with shims. In theory you shouldn't need shims but I like to be able to adjust it myself.