I just want to get my "ducks in a row" before I go back to my (never to be used again after this) machine shop. here is the back story: Pontiac 400 rebuilt to stock specs, 30 over pistons, 068 blue print cam, nothing special. Machine shop assembled the short block. Got the engine running, but it was making a knocking noise. Removed all of the accessories still making noise. Removed a valve cover while engine was running and saw NO oil coming out of the push rods for over a minute. Ripped out the idiot light oil pressure sensor and put in a gauge, reads about 10psi cold idle pressure, maxed at about 25psi when reeving.

So I removed the engine and put it in the stand flipped it over and pulled the oil pan. I noticed that when I rotate the crank back and forth the rods seem to stay put, like there is too much slop. So I pulled a rod cap and saw the cap bearing had major grooves cut in it and the rod end bearing was worn right to copper. (engine has about 3-4 hours on it)

I looked everywhere on the crank for a stamping as to what is was cut, found nothing. So I measured the crank with a micrometer and came up with 2.233 for the rod journal. I also measured with a set of calipers and got 2.235. I did this on two different rod journals, 1 and 6 I think, and it came out the same. This leads me to believe it was cut .015 under since factory was 2.25. I removed a couple rod bearing and found them to all be marked .010 on the back side. Pontiac specs for rod bearing clearance is .0005-.0025. So a .010 under bearing could have a inside diameter of 2.2405-2.2425 (I tired checking this but with the rods in the engine it is very hard to find the middle of the bearing, I came up with measurements ranging from 2.241-2.238 but I can't fully trust them). Assuming the smallest possible rod bearing, that leaves a clearance of about .0065 which is over double the allowable!!!!

I also pulled a couple main bearings and found that the middle of the bearing was worn clear down to copper. The crank journals and rod journals have ridges you can clearly see and feel very easily with your finger.

I would just like to know the next coarse of action. Should I try plastigaging it? (I have never worked with it before)

Any input would be great!!

Thanks,

Matt

Being a "hard core" Pontiac person, I feel the need to reply to your question. Most shops deal with chevy engines. Set ups and clearances are different than with a Pontiac (been there, done that). I see that you are in New York, so think about calling Nunzi. He knows Pontiacs!

I bought some plastigauge green, range .001 - .003.

I did a couple rods and they all came out at about .002, so that is ok, maybe alittle loose but ok.

I did all of the mains except the rear main and found the plastigauge was not even touched a bit. That means the mains are over .003 clearence. All of the mains show extreme wear, right down to copper, in the middle and moderete wear on the outsides.

So my questions is, are they the wrong bearings in the mains or did the low oil pressure from some other problem cause the mains to wear away enough that they are out of specs. I am trying to prove the machine shop did something wrong when assembling the short block, somehow I feel the machine shop will not take responsability and I am going to get screwed.

Thanks,

Matt

Main bearings that are worn down the middle and not evenly across the surface are usually the result of DIRT or contamination. I have seen this many times when a customer does not wash and clean the oil holes in a reground crank. The reputable crank shops all supply instructions for cleaning. Not all shops stamp the crank as to undersizes. Some (my shop) use ink stamps. Others use just a paper tag. It is the assemblers responsibility to check clearances.

Back to the bearings. An engine with that few hrs. on it should show no wear at all. Somebody left out a oil galley plug, wrong filter/adapter, dirty assembly or bad oil pump or combination of any. The crank is now junk.