The Stovebolt Site Forums The Shop Area Engine Shop Shimming main crankshaft bearings

Has anyone ever heard of shimming main bearings on a 235?

Had major engine failure with my 235 in my '55 210 doing 65 on Tour Nebr. in June--tick, tick, clatter, CLATTER, silence--3 holes in side of pan, nut came off of #6 rod bearing, bearing cap, rod, parts of piston in bottom of cylinder and pan, bent push rods, etc. Just started tear-down today and noticed the shims. Pulling crank, head, etc. tomorrow.

I didn't know that they were still using shims in 55. The process of adjusting the shims in the earlier motors is documented in the shop manual.

My 54 235 had shims in it when we tore it down for a rebuild, and we used shims when we put it back together. Plastigage is used to measure clearance, the shims are used to adjust the clearance. That was in 1976, and we bought shim stock of various thicknesses at the local hardware store. I wouldn't think the 55's would be any different, since they're both the full pressure 235's.
Samantha

Yes, my '55 had shims in the mains, too. The bearing set came with new shims.

Thanks for the quick response, guys.

Hope I don't find "machine shop" kind of damage tomorrow.

Picked up a '59 261 "supposedly covered after it was removed and previously running motor" as a backup plan. Unfortunately, upon draining the oil after getting it unloaded at the shop, we got some water out of the crankcase before the oil. Just hoping to get something back in the '55 before the driving season is over.

i take it this babbitt bearing's, not inserts ! babbitt bearing's can use shims when they scrape the crank journals and rod's .used to do it eon"s ago .

What is the serial number stamped on the distributor pad?
It is my understanding that there is a 55-1st series and a 55-2nd series 235. 2nd series and all later having the lower water pump that mounts in a largish hole in the front of the block. THis chaneg was made to accomodate the new lower profile 55 car with it's lower hood and radiator. These 2nd series motors do not have shims on the mains or rods. The bearing inserts are the roll-in type whereas prior engines had main bearings that are dowled into the main saddles.......correct?

Frank50,

You are correct about 54/55-1st high pressure engine still using shims for the main bearings.

Tim

OK Bill. It's good to learn something new everyday. Thanks for the link to the 55-2 shop manual. When then did Chevy change the 235 and eliminate the shims?

Arch, does all this help you any? I hope so. Good luck with your 55 210.

1955 was a change over year for six cylinder main bearings. Early engines had dowel type upper and lower main bearings, then later in the year they used dowel type lower and tang type upper.

All factory assembled Chev sixes up till early 1955 that I have seen had shims. I have not seen shims used on the late 55-62 engines, although the parts book lists them.

Do the shims extend all the way over to the insert or are they just under the mating surface of the cap? I have built quite a few AC tractor engines that used inserts and shims but they dont reach all the way in to the insert, they are just there to set bearing crush, which does not affect bearing to crankshaft clearance.

I believe 57 was the last 235 with main cap shims. From 58 through 62 they were completely shim free.

The '58 manual mentions using shims to set the clearances on the bearings, particularly if the bearing shells are replaced with the engine ine the truck or a new main cap is installed. Otherwise, it suggests grinding the crank undersize.