I have an LT1 engine that I built in 1976. Over the years it has gone through a few rebuilds, never a crankshaft endplay issue. I now have an issue. WIth the top thrust bearing in place and no cap bearing, I get 8 thousants end play. If I remove the top bearing and install the cap bearing, tighten it up, I get 0 endplay. I do not want to shave the cap bearing to get the required endplay, I want to find out the issue. Maybe a cap issue. I know if I buy a new cap, I need to have it line bored before I can measure anything. Would finding a cap off another engine tell me anything?

Bill Deliman

 

did the engine go bad? eat bearings? of just tired and you wanna freshen it? it takes a lot to hurt a main cap. do you still have the old mains? also, try a #1-4 main in it. not to run. to see if a torqued bearing messes with end play. betcha it doesn't. get plastigauge. see what you have for clearances. try another new set of mains. but i would take the needed couple thousandths off the sides of the thrust main that is making it too tight. buy a new main cap. get it line bored. put the same new main bearing in it. still .000 play. i had an accord that was using water. almost replaced the engine. it was the gasket under the radiator cap. don't start with the priciest and hardest thing. if you put a new crank in it, that main may say .000 start with the bearing.

 

I'm rebuilding it to take out the dome pistons and replace with flat top's. I bought a new thrust cap from Summit. It was manufacturered by Howards Cams.The bearing wouldn't fit. The bearing surface on my old cap was 1.530. The bearing surface on the new cap was 1.545, it is .015 too wide, so I called Howards Cams. They looked at the drawings and said the bearing surface should be 1.530, and I should exchange the cap. Another cap arrived, same issue, .015 too wide. I went to Chevy and their catalogs don't go back that far, so they couldn't find a part number for the original cap. Just wondering if I could find another cap, if that might tell me if my cap is warped somehow.

Bill Deliman

 

you talking #5 main bearing cap? what happened to the orig one? small block, 2 piece seal rear main cap?

 

Do this before you go nuts. Swap the upper and lower thrust bearing. I realize you cant run it this way, but lets make sure its in the cap and not a bearing issue.

Unless you spun a bearing or had some kinda catastrophic damage it shouldnt change.

If nothing leads to an AH HA moment I’d pull the crank and have it magna-fluxed along with having your block checked. Something is amiss here.

 

sounds like he has had thes block and crank together for many years. and tore it down to reduce compression cuz people who built motors in 1974 may be getting past the tire-smoking phase by now. he is saying new cap. i believe he means new #5 main bearing shell that has the thrust surface on it. it is possible someone packaged some bearings meant to compensate for end play wear as standard sized. so, Bill. have you replaced any rear main caps and if so, why? or are you replacing rear main bearings and they don't fit so you are blaming an engine you have run for 36 years cuz it is old and the bearing is new. get a set of bearings off amazon or autozone or rock auto or ANYWHERE but where you got these bearings. make sure they are different brand. the new bearings fit in the saddles and main caps? so the inside dimension is correct. it is the new bearing thrust surface that is too wide. the guy at howards cams said it is supposed to be 1.530 and it is 1.545.

 

I do not have the thrust bearing that was in the motor when I tore it down. I bought a new set of bearings and saw the no endplay issue. I bought a second set of bearings to see if I just got a bad set, same issue. If I put in only the upper bearing (block), I get endplay. If I put in both, block and thrust cap, I get no endplay. If I just put in the cap bearing, no endplay. I thought it might be a warped cap, so I bought a new cap made by Howards Cams and was planning on getting a line bore. It was the one that had the wide bearing surface. Had Summit send me a second cap, same issue. So that is a dead end. I just bought some plastigauge to check the journal clearance on the thrust bearing to see if that sheds any light on this. A guy at a local machine shop said the cap may be going on cocked. Without a crank, the thrust cap and bearings sits flat on the block. With the crank in, the thrust cap will rock side to side as if its pivoting on the crank journal.

I built the motor in 1976 for a 1970 Camaro. It rusted away, so I saved the motor and in 1985 bought a 1965 Stingray with a bad motor. I rebuilt my motor and dropped it in and drove it till about 2000. Started looking bad. Car sat for about 17 years. Started a frame off restoration about 3 years ago, thus the rebuild. Body work done, ready to reassemble.

Bill

 

with crank in. the main cap rocks on the journal. with crank in and no cap bearing, it sits fine? if you set the empty cap on the block deck, you can see and feel the cap in the spot it registers in? all points to the bearing. you have a spare unslotted #5 main shell now? drop it on a piece of sandpaper and make it fit. try both fully slotted upper mains and see if you have end play. your rear main cap is not the issue.

 

Bill, I’m assuming you have done this but I’m gonna ask just to hear myself ask it. Are you only initially running all the caps down finger tightish and then with a rubber mallet smacking the front snoot on the crank a few times and then rear hub of the crank the same and then torquing down?

If you’ve done that then its time to take the crank and block to a machine shop to see whats up.

 

i have never done that and never had a tight end play. he didn't hurt the crank or block. replaced bearings now has end play issues. end play gets bigger with wear. all engine parts wear so the clearances get bigger. they sell oversize thrust face bearings to compensate without welding the thrust face up. he has gotten 2 bearings from the same people. odds are they put oversize thrust bearings in a whole run of standard boxes. he needs to get a bearing set from someone else. different brand.

 

Is it possible that they increased the size of the thrust face over the last 35 years? Does anyone have a spare thrust bearing they can measure to see the thickness. I measure about 90 thousands on two different manufacturers.

Bill

 

Something is way amiss here. Could be a bearing issue but I don’t think so. Reread post 7, perhaps I'm reading it wrong but the way I'm reading it: If only the blockside bearing shell is in place there is no endplay issue. If both shells are in place with there is an issue. If the block side shell is removed and only the capside shell is installed then the issue still exists.

If thats indeed the way it is then there are only 4 things that could be wrong here

1. Cap not aligned right
2. Line bore out of whack
3. Crankshaft bent
4. Only 1 of the two bearing shells has a clearance problem

In a previous post i asked to see if he was able to flip the bearings around (top to bottom). Not sure off hand if you can do that (tang location) but if you can and the endplay issue doesn’t exist that would rule out the bearings.

He could try a different vendor of bearing but I’m really wondering if he has something going on like a tweaked crankshaft or something weird.

This motor has sat for 17 years. Things don’t go out of whack on their own, but who’s to say the crank flange didn’t get hit with something unknown to the OP in the 17 years its sat. I wouldn’t assume anything.

 

yes. because the 2 capside bearings are both too fat. take the 2 grooved saddle-side bearings and put them in and see what the endplay is.