The Stovebolt Site Forums The Shop Area Engine Shop bearing clearances on main caps

On my 1956 235 3100 Chevy motor, while torquing down the the main caps and using the platic gauge system I found the measurements to be .002". The Factory manual for the 1955 states clearances (Plastic gauge method) not over .0045” not less than .005” New bearing shell clearances should be .003” maximum and .0005” minimum. I also checked in the 56 supplement and it does not give any clearances. I realize that its too tight. I can not even turn the crankshaft.

I talked to the machine shop and they suggested in putting shims or I could do an alignment bore. Any thoughts on this? I am thinking of the alignment bore since i have invested soo much and a couple hundered more is just my guarantee that I did everything possible to have it correct.

Oh what are the two different clearnace for that the book describes? I understand the new bearing clearances but why is the other clearance listed? thanks guys I am getting closer to a finished motor.

I'd try another set of bearings (can you return them?) before I line bore a block.

Why did the shop not say to polish half a thou or so off the crank? Can you mic the crank journals yourself?

Plasti gauge is not super accurate... that's why they give you a wider range.

.002 is perfect...That would be the exact number you should be aiming for. You have other problems if it won't turn.

Shims! They were in my engine when I pulled it apart and I had to use them when I put it back together. I was told there were no over or under sized bearings for these engines.
Darren

you don't need shims, the journal bores are held to +or- .0005" as well as the crank journals. They make pretty much any undersize you might want at least down to .040" The other measurement would be for reassembling old parts. That is why when you order bearings from EGGE, you don't get shims for engines after '47, they don't need them.

I agree, .002" is perfect. I wonder if maybe you have one of the two center caps on backwards.
Also are you doing you spin test without the rear seal? If you have the rope seal in place it will be very hard to turn the crank.

Sorry I forgot to mention a couple of things. There were no shims when I took the motor apart and it appeared to be the original engine. I know it is period correct and it came from an older couple in Utah that used it on a farm. It sat for about 20 years. The motor was completey locked up when I tore it down. I had the block punched out .030 with new pistons. Lastly the crankshaft was turned .010 on both sides (main caps and connecting rods with the rods reconditioned. Every thing has been replaced except the crankshaft and connecting rods. Everything else has been replaced. The block and the head had been checked and magnafluxed. The replacement main bearing were purchased NOS at .010 and the manufacturer was Johnson bearing. The connecting rod bearing were purchased from Patrick's and they were cleviate, however I did not make it that far. I read they did away with shims in 1956.

I still do not understand this "(Plastic gauge method) not over .0045” not less than .005” New bearing shell clearances should be .003” maximum and .0005” minimum." why is there two different settings?

I think the .0005"-.0045" is for used bearings, and the .0005"- .003" is with new bearings.

the over .0045, and less than .005 would most likely be the limits for reassembling old parts. And the measurement for new bearings would be for assembling with well...new bearings.

hi dave

ok that makes sense. Thanks. lol I was too tunnel visioned I was thinking why put used bearing in duh never thinking about if you service the bottom end you still check it.

Ok now should I still align bore it and purchase new main bearings?

The NOS I had a buddy look at it and he storta did not like those bearings he said it just did not look right. One one of the bearings had a small gap from the base of the block right where the main cap goes. He told me about oil pressure and it could create a problem. No the seed is planted in my mind I am definately purchasing new main bearins. I do not want it to bug me on I should have done this. The machine shop recommeded align boring it.

Is there any drawbacks to align boring? I do not want to spend wasteful money however I do not might mind spending a few extra since what I have already invested I would kick myself for cheaping out and something broke.

The "not under .005" must be a typo as it should be not under .0005.

You should try each bearing by itself with the other three loose and the seal niot installed. If the crank rotates easily for each case but not with more then one done up, you have an alignment problem.

If your motor is supposed to have shims then the main bearings will have round dowel like projections on the back to stop them from rotating.

235's are strong blocks. I have never seen one that needed align boring.
I still wonder is you have a cap backwards.

you should be able to figure out what is wrong like nix and Dave say, the center caps are marked as to which side (end?) goes which direction the thrust has an R, which goes towards the rear, the 2nd has an F which goes toward the front. I would do a lot of checking before I line bore it, but no there would be no drawbacks except financial, it isn't the cheapest operation, as there is a lot of setup time, but it isn't horrible either, I had the block cut for a full circle seal, and he had it set up just the same as he would have for line boring, so I had him check the bores while he was already there. I can't remember off hand what the fella said for price, but given what I am certain you have spent so far it wouldn't be that bad. However the odds are pretty good you are fine.

This does have me concerned.

Dave, isn't it possible to get a couple of bearings in the wrong journal? (1 & 2?) or one half of one bearing with the other half of another? (different size) I don't think it would be possible, but do you have the top and bottom switched on one of them?

as the plot thickens


I checked the caps because awhile back I pulled the caps off without out marking them. I posted it at stovebolt here and you guys explained it to me about the "F" and the "R". You actually schooled me well. So I know thats correct.

The machine shop told me that it was 195 for the alignment bore



I went back to check to see if I mistyped but maybe the book is wrong, This is still all new to me and even with this hiccup I still love. Thanks again for the support. here is what the chevrolet truck shop manual 2nd series 1955 says, page 6-31 paragraph 6. If the bearing clearances is not over .0045" or less than .0005" the bearing insert is satisfactory. If the clearances is not within these limits, selective fit bearing by removing or insert shims. and paragraph 8. New bearing shell clearances should be .003" maximum and .0005 minimum. on page 6-85 in the engine specifications it says Main bearing clearances new .001" - .003" Used .001" - .004" Undersized .002" - .010" - .030"

I will post the pics of my caps

anyway you kids have fun, I'll check in in the morning, this is almost as good as building my own engine only it doesn't cost me anything.

I have definately made the decision to purchase new bearings. what I meant it was not flush with the block it was a little under 1/8" on the one side from being flush with the main cap. My friend was also worried about oil pressure. The guy helping me built many v-8's but really knew nothing about the 235. After we could not turned the crank after torquing it down we stopped and thats when I cam e here for advise. well that was on friday and saturday I went to 2 cars shows and decided to pick up where i left off yesterday and talked to the machine shop. you guys are the authority since thats what you fix and drive. I am thinking that it could be just some bad NOS bearings

here is the second main cap from the rear and I have "R" on the cap towards the rear main cap and not towards the front two main caps.http://i1291.photobucket.com/albums/b554/stovebolt56/2013-05-07_20-01-43_129_zps49b6b49c.jpg

What are these 2 dimples on each side of this bearing? This bearing I have the second one from the front and the "F" is towards the front main cap. http://i1291.photobucket.com/albums/b554/stovebolt56/2013-05-07_20-03-37_758_zps1c295aa0.jpg
http://i1291.photobucket.com/albums/b554/stovebolt56/2013-05-07_20-06-28_718_zps0f0a1c52.jpg

Is this what they call the dowel? http://i1291.photobucket.com/albums/b554/stovebolt56/2013-05-07_20-01-29_194_zpscfa013ad.jpg

When I took this motor apart it did not have any shims.

Ok I just pulled the crank and I know the bearing were not mixed up. I even verified the stamping on bearings to make sure that i was not given the wron set. I did not mic out anything because one i do not have a mic and the machine shop just tunred or polished the crank .010 on both sides. The onlt question is the bearing that fits around the main cap, Is that one suppossed to be in the second main from the front? http://i1291.photobucket.com/albums/b554/stovebolt56/2013-05-07_20-06-28_718_zps0f0a1c52.jpg

other than that I am stumped.

well if you guys can think of anything else I should try or look at just let me know. Thanks for all the help once again.

The dimples are to get oil to the thrust face.
Yes to the dowel question.
I will be thinking about the rest.

Ok fellow stovebolters, I have a theory and it might be my error. If my theory is correct.

http://i1291.photobucket.com/albums/b554/stovebolt56/2013-05-07_22-16-24_650_zpsffaaedff.jpg

The main cap on the left side is the second main cap from the rear with the "R" on it. The main cap on the right side is the second main cap from the front with the "F" on it. The bearing below was on the second main cap from the "F" on it. It looks like main cap with "R" was where it was supposed to go. However when I tried to put this bearing on the one marked "R" the second main cap from the rear it does not go on.

Could this be my problem that I but the the wrong bearing on the wrong cap?

Lastly I ahve search NAPA, Northern Auto Parts, Oriely's, and Autozone and they all say to use with the shim kit.

I do not remember any shims when I took the engine apart. Plus it appears I have a dowel at the 12oClock positions on the caps. The book says the 1956 supplement truck shop manual page 6-2 "The dowel in the upper half of the precision main bearing has been discontinued for 1956. A tang is provided at one of the butting edges of the upper new bearing. The tang which registers with a slot in the cylinder block and locates the upper bearing, also butts against the bearing cap to provent rotation of the bearing. The adjustment shims formely used between the bearing cap and cylinder block have also been discontinued. With the new tanged bearing and elimination of shims, dropping of the crankshaft in "Main Bearing Replacement" is eliminated for 1956 engines.

http://i1291.photobucket.com/albums/b554/stovebolt56/2013-05-07_22-43-51_737_zpsc223af16.jpg This is the block side of where the second main cap from the rear goes

http://i1291.photobucket.com/albums/b554/stovebolt56/2013-05-07_22-44-00_816_zps19a5cf91.jpg This is the front main cap goes.

http://i1291.photobucket.com/albums/b554/stovebolt56/2012-08-12_22-34-36_478_zpseb01f2a3.jpg this was before it was cleaned and painted but I just wanted to show the serial number on the motor 0365I39 F56X

the bearing with the dimple is the thrust bearing it goes on the journal with the R on it. (that is why the 3rd journal has the front and rear face machined) So there is your problem, the gap was because all the journals are different size (smallest in the front, getting larger as they progress through the block.)and if you had the thrust bearings on #2 and vice versa (I didn't think that was possible) you probably ruined the thrust bearing as you were trying to squish it into a significantly smaller hole than it was supposed to fit in. Oh and by the way don't use the lube UNDER the bearing, it will interfere with your clearance readings, the interface between the block/caps and bearing shells should be dry. make sure you don't mix up tops and bottoms of different journals, as I said before they are all different sizes and although you can get them in the hole it don't mean it is right.

After I pulled everything apart it sorta looked like that my friend with the v-8 experience set the bearings in place because i did not know what the heck I was doing but i can not throw him under the buss i was there too I should have noticed that. Yes i agree we did not put lube under the bearing i think after trying many different things it sorta seeped into the hole tomorrow I will order a fresh set of bearings and try it again. But it still leaves me the question with the shims. from the photos you can see the dowels is the 56 chevy supplement wrong about the shims?

No shims

You do not need shims unless the crank was not turned to the correct size.
Checking bearing clearance with Plastigauge will answer that question.

Not sure if the 235 is more precision machined than my '52 216, but my 216 definitely had shims and needed shims with new bearings. I would check each bearing without shims. My measurements varied from nill (locked up crank) to .002". Once I got all the clearances correct at .0015-.002, the crank spun freely. Upon installation of the rear rope seal, I could not turn the crank by hand.

Same process used for each connecting rod. The engine is very tight with the rope seal.

Just to clear up the shim topic, Chev stopped using shims in late 1955 except on the rare occasion that the machining was off a tad and the crank did not spin on assembly, than a shim or two was used.

Well all i can say at this point is oops at least i found the problem. I guess i will order the new bearings and install them in the right location my then using the plastic gauge check the tolerance. Maybe give it a spin without the rope seal. Put everything back to normal. If i need the shims i will order them but i am now confident that i probably will not.

Once again you guys came though and thanks again. This is a great learning experience i am still enjoying the build.