WTF? Deposits in piston....

[mullett]

Pulled the head of my GZE (165,000 km...and I can still see the cross hatching in the bores. Hooray for Toyota!)

But that's not the point...what the hell are all the flakes left in my pistons? There's a few grams, only in the middle two cylinders. Is it the ceramic coating off the piston, or something bizzare happening before the piston, or is it something left over after a burn? I'm stumped...here's some pics.

[30psi 4agte]

why did the head come off ??? BHG ??

does look strange .

Is it actually small dents in the piston or is it something that can be cleaned off ?? ( carbon build up )

[NVD05X]

looks like dents in the pistons... :s

try a bit of carby cleaner on a rag and see if it comes off...

[mullett]

It's totally loose, you can pick it up with fingers. The headgasket was fine, came off for a better head to go on. The deposits are extremely brittle too, like carbon? What could cause that, especially just in a couple of cylinders?

RM.

[NVD05X]

did you do a compression test before you pulled the head off?

[mullett]

sadly, no. Is it possible that this is the ceramic coating from the pistons shitting itself and flaking off? Or something more sinister that I should freshen up the engine for?

RM.

[oldcorollas]

try and burn the black stuff
no, seriously...

carbon will burn off stuff (according to my experiments ) at about 920-930deg, but thin material like that should burn easier.... if it just gets hot and is not affected, then maybe it is ceramic...
i would be betting on carbon...

maybe spray some WD40 in there and leave overnight.... if it all crinkles up, it's prolly carbon/ash deposits..

[kingmick]

it is oil from stem seals or rocker breather! been that way for awhile!

[mullett]

Had a think about that, it's worth noting that it didn't take any oil from one oil change to the next. How much would the stem seals leak?

RM.

[jonra23]

What is plumbed into your intake manifold that would be being directed more to centre intakes, PCV valve or similar?

[mullett]

Hmmm...good question. The stock GZE intake favours the centre pistons, for sure, but if it'd been coming from the intake I would have thought there'd at least be a little bit on the outer pistons. Nothing is in the runners that I can think of, so everything that goes into the ports comes through the inlet pipe or the injectors...

RM.

[oldcorollas]

what do intake ports look like? any black marks starting after the guides? doesn't take much oil over 165Kkm

[mullett]

Just had a look, near the valves and back it's perfectly clean, but at the entrance to the ports there's a black residue, like dirty oil, in the shape of a triange tapering out for about 4cm. There's more on the middle ports, less on the outer ports.

RM.

[jonra23]

"dry" manifolds on EFI systems aren't designed to keep a homogenous mix of vapours in intake air like a carby setup is, recon if you track stain back through intake system you wil find source, my guess would be PCV or similar.