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Get a number punch set for the main caps or a center punch will do.
Take it slow.
The main caps are numbered 1-4 on one side except for some odd reason GM put the number 5 rear cap on the opposite side. Just remember the wings on the caps point to the rear of the block with the exception of number 5 which faces the front of the block.
I'd guess number 1 and number 5 main caps are manufactured exactly the same process and specs. Since the 5 wing faces opposite it is simply struck with a different (5) number die and inverted during line honing then assembly to face forward.
Last edited by RedXray; 06-25-2020 at 03:09 PM.
Reason: added a guess
It was hot today but got the thing out and pulled apart the top end. Everything looked good except one of the head alignment dowels looked like it was mushed. As well as one pushrod that had some strange wear on its side. Spun the crank and the cam looks good on all lobes! Probably pull the bottom apart tomorrow.
Last edited by dantheman1540; 06-25-2020 at 09:05 PM.
Is that munched head dowel on the same side as the blown gasket????
Yes it is. The head gaskets this time look great but that could very well be the cause of the previous failure. Although it was the the #4 cylinder that had the gasket failure and with a jacked up dowel I'd assume it would fail at the closest cylinder.
What bit of the timing chain I could see looked good and the pistons seemed to move like they should when hand turning the crank. I'm guessing a main bearing must have spun or the whole motor is fine and I should have diagnosed more before I pulled it.
When you get it on the stand and remove the oil pan, usually you'll see silver specs of aluminum if it's ate a bearing. I've seen noise come from flywheels, flywheel bolts, balancer, water pumps etc. that mimic engine knock.
Funny story back in the early nineties I was over at a friends house. This guy Jimmy was born in Greece and did shadetree wrenching on the side. All the local Greek people brought their cars to him for mechanic work because he could explain to them in their native language what was wrong with their cars. I'm sure they trusted him more than any average garage.
This old guy pulls up in a nice Cadillac Eldorado. He's just come back fro the Cadillac dealership where they diagnosed a knock and told him it was the bearings with an estimate of $8,000 for a new motor. While Jimmy was talking to him (gibberish to me) I wiggled the fan blade "It's only the water pump" I interrupted. When Jimmy confirmed that guy was shaking my hand patting me on the back while cussing the dealership "You come to restaurant any thing you like, please please come to restaurant I fix you up"
I never actually heard any knocking. The motor just nosed over and dropped to a 200rpm rough idle I then shut it off and coasted to a stop. I only ever tried to start it one time after that in which I heard so grinding noises and it did not start. When I did a walk around of the truck I saw what I thought was little metal pieces in the tail pipe, but now I think it may have just been sand particles as the pistons don't appear to have eaten anything. I very well may have jumped the gun on pulling it but since I recently pulled a bunch of parts off it to diagnose/repair my tahoe it was already part way to being pulled. Plus I've been a little uneasy about running to stock pistons. Even if everything is okay I will likely get a set of drop in forged pistons possibly rods as well.
All the bearings look good, cylinder walls look good and piston rings look good except one thing, the rings seem loose. Not sure what they are supposed to look like but I assumed seated rings would be kinda stuck in place and not sliding all over the place all ***** nilly. Rings would explain the severe exhaust smoke leading up to the shut down incident.
The wasted dowel may allow the head to misalign to the block. Probably wouldn't affect the head gasket the way it looks, since it's not too drastic; but might affect intake gaskets.
I'd get new dowels if I was doing this. I always do anyway. They're like $10 a set at Summit IIRC, and require essentially no skill, effort, or tools to swap.
Rings should be fairly free to spin around, esp the compression ones. Oil ring may be a bit stiffer. In fact that's the reason for the "cross hatch" in honing the bores: the rings are SUPPOSED TO spin around the piston as they move, caused by that.
Well I have everything loaded up and ready to go to the machine shop today, still didn't find anything obviously wrong but maybe they will find something. Heres some random pics I took along the way with oily hands.
06-25-2020, 12:50 PM
