Finally got my head off

[Eriol]

I know, took me bloody long enough. Wasted most of this afternoon driving around looking for a 14mm hex socket or allen wrench -- finally found one at Autozone.

The head gasket didn't look too bad to me, but I'm a newbie. What do you guys think?

The #5 cylinder (on the right in the above pic) was the one that had low compression.

The back-story for those who don't already know: at first, the car would overheat at prolonged 90mph+ driving, and the problem got worse until it got to the point where it would overheat during 2 miles of mild driving. I replaced the water pump, and the problem seemed to go away for a few days. Then one day I glanced down as I was driving, and saw that the temp guage was pegged. I pulled over, and steam was blowing out the side of the water pump. I only drove it once after that, and it started getting hot within a few blocks - less than the time it would take the engine to get warm. Ran a compression test, and all cylinders were between 155-170psi, except #5, which was 75psi. There was never any coolant in the oil or vice versa.

Luckily, the head doesn't seem to be warped, if my ghetto test done with a cigarette and a laser-pointer is any indicator. I'll take it to a machine shop tomorrow and have them check it with a precision straight-edge. For now, I'm off to the bar to celebrate.

 

[Supraboy89]

looks like on #5 the copper water seals on the gasket could have been leakin on the exaust side. also check your raidiator for blockages. a bhg can make a lot of trash and gook get in there. also looks like you have some excess oil in #5 too. could be bad rings

 

[Kckazdude]

#5 & 6 look like they were blown to me. THe water passages are deformed on both of them.

 

[Supraboy89]

#5 & 6 look like they were blown to me. THe water passages are deformed on both of them.

true

 

[Eriol]

So it's blown if the water passage seals are deformed, even if the seals on the piston side are OK?

Really off to the bar now.

 

[Kckazdude]

No, they are blown from cylinder compression pushing them out.

 

[Supraboy89]

No, they are blown from cylinder compression pushing them out.

what he said

 

[Eriol]

Cool. BHG it is, then. As for the oil in #5:

The pistons all look pretty nasty. I just figured that was because it's a ~150,000 mile motor (not sure exactly, I know it had 120,000 when it was put in the car, but I don't know how many miles it was driven after that). No pools of oil or anything, though.

I'm not too worried -- this is just a stopgap, there will be a Supra with a built motor in my future. I've already started collecting parts.

 

[Eriol]

Sorry, I'm used to philosophy classes where people are more than happy to pick apart my statements and tell me why I'm stupid.

I will rephrase as a question:
Is it normal to have that much crud on pistons with ~150,000 miles on them?

There also seems to be a lot of crosshatch remaining on the cylinder bores - you can even see it in the first pic in the original post. It feels smooth if I run my fingernail over it, though. Is that normal?

 

[Kckazdude]

On an improperly tuned/running motor there will be plenty of crud on the pistons. Considering you had a BHG and probably some well worn plugs it isnt surprising at all to see pistons like that. Without doing a leak down test or measuring the ring gap it is hard to say what shape the rings are in. The crosshatch is so fine you wouldnt be able to feel it when freshly done. The stones usually vary from 400 - 600 grit.

 

[Eriol]

On an improperly tuned/running motor there will be plenty of crud on the pistons. Considering you had a BHG and probably some well worn plugs it isnt surprising at all to see pistons like that. Without doing a leak down test or measuring the ring gap it is hard to say what shape the rings are in. The crosshatch is so fine you wouldnt be able to feel it when freshly done. The stones usually vary from 400 - 600 grit.

Hmm, that makes me sad. It was well-maintained by me during the 20k or so miles I drove it, but I can't speak for previous owners. I wonder if the oil crud on the pistons and the crosshatch on the bores indicates an improper break-in?

 

[Eriol]

Illustration:

The crud is pretty uniform across all 6 cylinders, including the ones without HG trouble. It is slightly worse on cyls 3, 4, and 5. It has the consistency of very dry tar.

Crosshatch on cylinder bores. I'll grant this is the first time I've had a running motor this far apart, but I'm thinking that's not supposed to look like that.

So... improper break-in?

Argh, I wish I had a garage big enough to pull the motor and rebuild it. Not this year, though.

 

[supramang]

MMMMMMMMM well dont these pictures look too familiar

 

[jdub]

The cross hatch is normal, unless you are burning oil...based on your compression numbers your rings are sealing fine. You can clean the piston tops with Mopar Combustion Chamber Cleaner.

Are you planning to replace the HG with a stock composite or a MHG?

In either case, get some ARP head studs.

I know you think there is no coolant problem, but I would change the oil before you run it again. ANY coolant in the oil is bad for the bearings.

 

[Eriol]

The cross hatch is normal, unless you are burning oil...based on your compression numbers your rings are sealing fine. You can clean the piston tops with Mopar Combustion Chamber Cleaner.

Are you planning to replace the HG with a stock composite or a MHG?

In either case, get some ARP head studs.

I know you think there is no coolant problem, but I would change the oil before you run it again. ANY coolant in the oil is bad for the bearings.

Cool, thanks for the tip.

I'm going with a composite HG for now, there will be a full buildup with forged pistons and a MHG in the not-too-distant future. Oil was drained before I started working, and I'm going to change it again shortly after I get it running again in case I got any crap in the oil passages in the course of cleaning the block surface.