Hello all,

I am in the process of tearing down a 84 J code 6.2l and I am at a cross roads. I am pretty sure the passenger side cylinder bank head gasket was shot. there was coolant in the #4 cylinder. I do have a question about what I am seeing with the head off. # 8 cylinder has a white goey substance on the pistons and from what I can tell is in the pre chamber also. What is this stuff and what is it telling me?

Anyway all the cylinders look pretty good except the #4. near the top it looks well ... not ideal. my thought since I am trying to keep costs as low as possible was to hone the #4 cylinder only and install new rings. My concern with this is during honing I may exceed the piston to wall clearance spec. I have found what is called hi limit pistons that are supposedly a couple thousands larger than standard pistons.

Any input would be much appreciated.

I can post pictures if needed.

 

Id get the block and heads magnufluxed for cracks if no cracks it was just a bad head gasket. and you will have to hone every cylinder tht u install new piston rings.. if u dont hone cylinders and install new rings there will be bo crosshatch patteen on cylinder wall for the rings to seat right and youll get excess smoke out your exhaust from oil burning.

 

There was when I took the heads off there was about 1/2 cup of coolant sitting in the #4 cylinder. for this much to be in there wouldnt I see a crack in the head or the cylinder wall. I will also add that how I found the supposed gasket was bad because I had a profuse amount of water coming out of the passenger bank exhaust manifold. I didn't drive it enough to see other usual symtoms.

 

Yeah look close at the precups inbetween valves on #4 cylinder head ...if u dont c one then it eas most likely a bad gasket.. for a replacemebt gasket dont use fel pro get victor reinz head gaskets and use copper spray a gasket in a can n just spray each side of gasket with onr coat. you will also have to buy new head bolts the stock ones stretch over time. gm advises to buy new ones after heads are removed..and depending on how much you wanted to spend arp head studs would be even better ...but follow what i judt listed and youll be all good to put tht detroit back on the road.

 

*2,get the block and heads crack checked and pressure tested.

Muck in cyl #8 could be the sign of a cracked block.

A lot of coolant in cyl #4 would make me get that connecting rod checked for straight also,liquid can't be compressed so something has to give unless it was able to escape through the gasket leak.

 

First off I check the #4 cylinder head and there is no crack.

Is there any check I can do myself to check and see if the rod is bent other than look at it. I am pretty sure that much leaked in there while I was labeling wiring and getting it all out of the way before i pulled the motor. btw this process took a couple weeks as I work long hours usually and something was going on like every weekend.

If I had known I had coolant sitting in the cylinder I would have made it a priority.

 

Rotate the crank to bring the piston to top dead center,if it is flush with the deck,or at least the same amount below deck as other pistons @TDC-the rod is probably OK.

 

thanks racer55. I just checked it and it looks good. Hey I also figued out what the white goey stuff was. Apparently when you let wd-40 sit for awhile it turns into white goey stuff. I have been used wd-40 to keep the block from rusting and I had wiped and the previous goey stuff off and it came back since using more wd-40. so mystery solved there. I am leaning right now towards honing out the cylinders just enough the get them to clean up. Anyone out there know what the upper limit is for piston to wall clearance on a 6.2l diesel or even a good rule of thumb for this spec when it comes to diesels.

 

The military manual listed under-"repair manual" at this offsite location should give the specs you need:
GM 6.5 FAQ & Information Sticky "Look In Here First" - Diesel Place : Chevrolet and GMC Diesel Truck Forums