Piston damage, how bad is it?

[farmerz24]

remember the damage may not seem as obvious as if you pulled the piston. the side walls/skirt could be damaged aswell.

check out this pic. the side of the piston was actually still on there, being held by the block. as soon as i pulled it out i noticed this. and from the top view while still in the engine i could see something similar to what u saw.

check the pic. this was a ticking timebomb.just saying your damage may be more extensive than it seems, and if the piston explodes i think you kiss your head good-bye.

[Joseph Upson]

If the piston ring is not broken you will probably not have any trouble out of it. The pistons from my 3.4 in my Fiero were far worse than that from severe detonation caused by a loose ground strap. The engine was turbocharged and some time later it finally started loosing oil under boost from the valve cover otherwise it ran fine.

When I took the heads off intending to change the piston rings with the engine in the car by removing the oil pan and pulling the pistons out the top, I couldn't believe what I saw given the way the car ran; 3 chipped pistons, two severely to the point where not only was part of the outer lip of the piston missing but so was a corrasponding section of piston ring and the ~.030 groove cut into the cylinder bore is what allowed the excessive pressure into the crank case. Had the ring not broken I probably would never have known there was a problem.

The pieces went through the turbine housing causing very little damage, probably because the pistons processed them by crunching them against the head before they exited the exhaust port. I did have a few occassions where for some reason the electrode on a few plugs were bent, I thought the detonation had caused it.

If the pistons in the 3400 are made out of the same material as those from the camaro 3.4L they are very strong because the detonation I subjected the pistons to several times before eventually discovering the disconnected ground strap was the equivalent of rapidly tapping the intake manifold with a wrench, very loud.

Each bank of pistons has there own ground at the ECM so the strap left disconnected must have represented the three pistons that were damaged.

[dnalbach]

Judging by farmerz24's pictures it looks like I should definitely check the pistons for hidden damage.

What is the exact procedure for doing this with the motor in the car and the heads off?

1) Take off the oil pan.
2) Somehow unbolt the piston from the connecting rod? Special tool or just a small wrench? Anything else come before this step?
3) push piston out the top and examine it?

Same thing in reverse for reinstall? Someone said cylinder honing? I've never done anything with pistons before.

Probably should replace the piston rings on all of them while out?

[Superdave]

after you take off the oil pan you'll see the windage tray, 8 nuts to remove that.. then you'll see what's in the pic...

you'll just have to get the 2 orange painted nuts loose on the rod cap, with the nuts still on there give them a few light taps with a hammer to pop the rod loose from the bearing. then remove the nuts all the way. then you should be able to push the rod/piston out the top.

on a 3x00 engine i believe the only piston you can pull out the bottom is #1 (with the crank removed), i'll have to double check on that... lol

for the install of a new one, you will need to rent a ridge reamer, it just shaves down that ridge of crud at the top of the bore, a new piston is about $35 or so plus rings. Also rent a hone to make sure the new rings break in right. If you have any friends who've built engines they'll show you how to hone the right way and use the ridge reamer as well.

[dnalbach]

Thanks Superdave, I really appreciate that explanation with the picture. I don't have many automotive friends, but maybe I can find something online about the ridge reamer and hone.

The rings aren't a problem, but where do I buy pistons? The auto stores around don't seem to carry them. GMPartsDirect is about $70 each for pistons. Should I try to replace them all, or only ones with obvious damage?

[Superdave]

you should be able to get a piston from any auto parts store...

i'd just replace the damaged one if that's the only one.

can you get a good picture of the piston all the way down in the bore?... just want to see if there is any damage to the wall...

[dnalbach]

I have a picture at home looking into the bore and there was no damage to the wall, but piston #2 was only about halfway down, so I can only speak for the upper part of the cylinder wall that was showing. I'll post the pictures when I get home from work.

[dnalbach]

Here are pictures of cylinders 2, 4, and 6. I don't have the front head off yet, but will on Wednesday (I work Sat-Tues). The pics don't show the cylinder walls very well, but there was no obvious damage to me like scratches or gouges. There is a little bit of coolant around the edges of the pistons. Long story.

Piston #2 with the chip, but looks better than the other two pistons



Piston #4 looks slightly burned



Piston #6 Looks like it's been blasted, is that normal?

[sil]

the stuff inbetween the piston and wall looks like burnt piston lol

[farmerz24]

i would pull them out from the top just to be safe.! you never know what youll find.

[dnalbach]

Stuff between the piston and the wall is coolant, I couldn't get it all soaked up with towels when it spilled into the chambers.

I'm going to take your advice farmerz24 and pull them all on my next off days and see what's up.

[bszopi]

Is all of this in the Ciera wagon you have mentioned in previous posts? If so, have fun pulling the pan with the engine still in the car. The 3x00s have cross-bolted mains, and the back 2 side-mount bolts are almost impossible to get off due to the tranny being in the way. People have done it before, but it is far from easy...

[dnalbach]

Yes it is the 95 Cruiser wagon. I didn't know it was that hard. I was under the impression that the A body was easier.

[dnalbach]

I got the front cylinder head off today and everything looks fine. The head gasket was a bit clogged, but fully intact, and there was no visible damage to any of the pistons.

Piston #2 really bothers me, but I've decided that I can't drop the oil pan in my apartment complex. It's just too hard. If I had a garage and an engine hoist, I'd go for it, but out in the parking lot it's just not going to happen. It's a miracle the apartment manager hasn't towed me already, and I expect it to start snowing in a few days. So I'm going to put it back together and let it go until next summer. Hopefully it makes the next 8 months as is.

Thanks for all the help and good advice.