What do your piston tops look like?

[Ross]

Just looking at the tops of my (Ej25 DOHC) pistons through the spark plug holes, they look much rougher than I've seen pistons looking before.

 

The surface almost looks pitted/corroded. Many small 'craters', between 0.5mm and 2mm-ish in diameter, not very deep looking. Similar on all pistons. No mechanical damage to spark plugs so it's not like there have been any foreign objects in there.

 

All this is just from looking through the spark plug hole so it's hard to tell exactly what I'm seeing.... The motor runs fine (well, it missfired a bit, but I'm attributing that to the ancient spark plugs with 1.4mm gaps...).... ANy Ideas?

[OB99W]

[...]All this is just from looking through the spark plug hole so it's hard to tell exactly what I'm seeing.... [...]ANy Ideas?

I don't know exactly what you're seeing either, but if black, it could be carbon buildup. If metallic, could be due to detonation (running bad fuel, anyone move your knock sensor -- or replace it with a resistor?).

 

If black with metal showing in spots, could be detonation impacts on a carbon layer.

[markjw]

I don't think it's anything to worry about. Every engine I have pulled apart has a fair amount of build up on top of the piston's. The craters your seeing is most likely carbon build up. I bet if you had the head off, you could scrape the stuff off.

 

If you see one in there that looks brand new, then you should be worried.

[idosubaru]

I don't think it's anything to worry about. Every engine I have pulled apart has a fair amount of build up on top of the piston's. The craters your seeing is most likely carbon build up. I bet if you had the head off, you could scrape the stuff off.

 

If you see one in there that looks brand new, then you should be worried.

+1, that's about my story too when i pull heads.

 

is the motor is out? did it sit awhile? and why are you concerned? i don't make any effort to view all the piston tops in perfectly good running motors, even ones that are easy to do, unlike the DOHC EJ25...so is something else going on?

Edited November 6, 2010 by grossgary

[Ross]

No, I'm not concerned, the motor is out because I'm doing a little juggling around with two crap cars to make one good one. Just had a peak for interests sake and thought it looked a little abnormal.

 

It may well have more carbon build up than normal due to the misfire it had (spark plugs -- hopefully....). In any case, I'm not doing anything about it, it's a good engine and it'll be going straight back in once I've stopped it leaking from every orifice..