What did you do with your GMT400 today...or yesterday....

[dbrannon79]

They look like they are a much better design than the button type. springs keep them in place, I guess one of those springs would have to break for them to walk off the valve or push rod. Not sure if they are cast iron or aluminum, I would need to clean them off to see.

Heads will need to come off to see if the valves are the problem or the heads are cracked, but worst case scnario I have the heads that are on the other 6.2 or the heads that are on the 6.5 that's in 93. I know the ones in my 93 don't have coolant issues and the engine runs so that's a plus I guess. the other 6.2 will also run and had a round about 250-280 compression but I never hooked a cooling system to it, only ran the garden hose through it to run the engine for a while on the stand.

 

[dbrannon79]

looking at some of the things on this early 6.2 being the rockers and the starter bracket both which seem a lot stronger it would seem like GM put in a lot of effort in designing these diesels in the beginning and then cheaped out on a lot once they were out on the market! Dam those GM bean counters!!

 

[MrMarty51]

I was give a case W9 loader. Engine was seized. Pulled injectors, knocker loose into each cylinder. It tirned over a 1/4 turn after about a week.
Its a four cylinder.
Valve stems is rusted into the guides.
I got back to work and never had a chance to finish getting the hood removed(cab and fuel tank filler is holding it from sliding back far enough) so to get the rocker covers removed.
I have a few days off work now so hope I can get back out there and see if them valve stems can be gently made to move.
That was the problem @dbrannon79 s engine

 

[dbrannon79]

I had thought about it this morning of trying something that would help dissolve carbon like some berrymans B12 spray into the intake ports of the head, then using my blow gun in the port while tapping on the valve stem. if it's carbon deposits and they can be cleared that way maybe I won't have to pull the heads right away.

 

[Paveltolz]

I know you’ll clean things up regardless but, a magnet would help determine if your rockers are iron or aluminum in the meantime.

 

[Will L.]

That is the original type rocker arm. Yes most of us old dudes prefer that to the button type.
Both type can become “bent” out of the 1.5:1 ratio. It is rare but happens with the intake faster than the exhaust ones. So how we did the check was simply take apart, clean, and use one to make a jig on a work table that had the center shaft hold it, and have a piece of steel tacked in position where the valve would be, and another where the pushrod sits.

Not super accurate but would show when one is out of shape. Usually only one would be, and quite often there was a mark where a valve kissed a piston- so my opinion became it was from that not just time that got it to bend.
Anytime I see valve to piston- everything that moves becomes suspicious & gets checked by measurement-even if just measuring compared to others in the engine.

Do you have an actual leak down tester?
Not hard to diy one & watch couple YouTube videos to see what to do if not. That is your next step imo.

I would fight to use the 6.2 heads over a 6.5 head. I would rather have 6.2 heads rebuilt than buying new 6.5 heads unless it is p400 heads. They simply flow better which is better power, better mpg when you keep your foot out of it, lower egt, better rocker arm system.

 

[dbrannon79]

Don't have a leak down tester, but with all the rockers loosened, the two that had zero compression blowing into the GP hole with my blow gun and rubber tip it all comes out the intake port of the head. the others all have "some" air that goes out the intake ports. the only two that hold really well are the back two on the drivers side. #'s 5 and 7

 

[dbrannon79]

I figured I would go ahead and pull the rockers completely off where I could tap on the valve stem with a hammer. then on the two that have no compression, start blowing in the GP hole and tap, tap, tappity tap on the intake valve. since those two won't even build enough pressure to send the piston down with the air gun. if that works, then work on the rest. and once that is done, re-do the compression test.

I think the valves are where all the compression is going. even on the ones that have semi-good compression (300 psi) I can feel and hear a slight amount of air coming from the intake port. I am sure some is also going out the exhaust too. I haven't pulled the exhaust manifolds off yet.