M20 headoff , combusion chamber marks very odd

[Chisum]

Pulled a 91 2.5 head off at the junkyard, and the surface of the head is smooth enough, but the chamber part on all but one cylinder has little cut marks or pot marks in the combustion area. Dozens of them per cylinder. Very strange. The little marks can be felt, they are on all but one of the cylinders. They are on one side of the chamber. I'm sure I can smooth them out with a small file and they won't affect compression, but what the hell caused this? Anyone else seen anything like it?

[Zyth01]

Often its because of debris floating around while the piston is going up and down and it smashes it into the top. A small amount of dents is tolerable just make sure none of them are real sharp and capture heat.

[Dyno4mance]

It sounds like pits made from extreme detonation.....were the plugs still in the head?
Did the pistons in the motor desplay the same pits?

[Madhatter]

i was going to say, if it looks like a battle field with all these little holes (especially towards the ends of the crown), its detonation damage.

[Chisum]

My first thought was debris. I Didn't check the pistons that closely. The plugs were/are still in although I didn't check them that closely. I've never seen that before although to be honest I never pulled an aluminum head before.

[Chisum]

i was going to say, if it looks like a battle field with all these little holes (especially towards the ends of the crown), its detonation damage.

Definitely battlefield scars.
If you are referring to the "hump" or high spot of the chamber I will check to be sure, but I recollect that was the area. What causes that? Bad gas? Old gas? Too low octane? Timing issues?

[AlarmedBread]

I would guess the injectors were not flowing quite as well as they did 20 years ago. ;)

[digger]

Pulled a 91 2.5 head off at the junkyard, and the surface of the head is smooth enough, but the chamber part on all but one cylinder has little cut marks or pot marks in the combustion area. Dozens of them per cylinder. Very strange. The little marks can be felt, they are on all but one of the cylinders. They are on one side of the chamber. I'm sure I can smooth them out with a small file and they won't affect compression, but what the hell caused this? Anyone else seen anything like it?

you haven't posted any pics so how do we know if we've seen anything like it?

[e30this]

Did it look a little like this??









I had this happen in one of my motors.
This was caused by the PO installing Bosch Platinum +4's into it before I bought the car.
I had it for 2 weeks then this had happend.
He said he installed the plugs the week before I came to get it.

I dont think it could have been anything else that wouls have caused this to happen.
None of my valves was bent and the head was fine. The cylinder walls are perfect as you can see and I pulled the piston out and all the rings and bearings was still perfect.

[Chisum]

I can take pictures but Im not sure how to post them up here. Can anyone help in that respect?

[DarkWing6]

I can take pictures but Im not sure how to post them up here. Can anyone help in that respect?

When you reply you will see "Manage Attachements" below the box where you type. Click on that tab and upload the pictures. After they have been uploaded click on the paperclip pictured above the box where you type. Click on each of the picture names to add it into the post.

[Chisum]

Here goes...

[Chisum]

When you reply you will see "Manage Attachements" below the box where you type. Click on that tab and upload the pictures. After they have been uploaded click on the paperclip pictured above the box where you type. Click on each of the picture names to add it into the post.

Thank you. Worked like a charm..

[xLibelle]

detonation. and because its not seen in one cyl is because it wasnt firing, or getting fuel, from the looks of those injectors.

[h82crash]

That is detonation and what usually happens is the ceramic insulator breaks off the sparkplug and gets pounded in the head and piston. So...the spark plug didn't break in the one cylinder. That doesn't look too bad either, that can be smoothed out with a die grinder with a rotory Scotchbrite pad. The head I had was worse and I smoothed the sharp edges and she runs great. (2.7i build)