Damage top of the Pistons?Investigation help!

[popdemonic]

I pulled the AAN head off today.i planned to swap another rebuild head in.
unfortunately,i found there's a lot pitches on the top of #1 2 3 pistons as you
seen on the photos.the #3 is the worst volunteer.Can anyone help me investigate
if the top of the pistons damage due to some metal fell off or the Detonation did this.
my car is running on VEMS standalone and E85 biofuel.I occasionally heard some kinda
knock when WOT.i had been running 034 software back in the day and the knock noise
seems much more worsen but never got any pistons damaged just like this one.I checked the spark plugs,all is great shape.i still couldn't imagine if something could
fell off into the chamber.






piston#1



piston#2



piston#3



piston#4



piston#5



Head..





turbine wheel looks fine.





compressor wheel looks fine



ignition timing table.max boost is 270-280kpa.

[Thuppu]

You really shouldn't hear any knock with e85. Looks like quite a lot of timing there.

[popdemonic]

Thomas,
I will be pulling my timing back 10deg whole table.i start to think its
caused by detonation.lesson learn.the good thing is i found this before
Some worse case scenario happened on cylinder walls

[SteveH]

It's hard to tell from the pics but it looks like particles of metal stuck into the pistons and not missing material. Not sure it's detonation...

[rst]

What fuel injectors are you using? There is quite a lot of tar on the pistons. I have seen this kind of tar before when fuel injectors spray angle was to narrow. Is there any damage on cylinder walls? It looks more like something went through the engine rather than detonation damage.

[Thuppu]

Only squish area smashed... If there have been a object inside there should be some marks also elswere.

[pasbogdan]

Thomas,
I will be pulling my timing back 10deg whole table.i start to think its
caused by detonation.lesson learn.the good thing is i found this before
Some worse case scenario happened on cylinder walls

Not sure from the pics,but bores look like a +/- 0.05 mm wear.Also no honing marks?

[orignalS60]

The marks are only on the area where
your valves go over the pistons. The valve
relief area. I'd say your valves have just been
kissing the top of your pistons. Not that bad
though. When I over revved a 2.7t motor
the tops of the pistons looked like swiss cheese.

[pasbogdan]

The marks are only on the area where
your valves go over the pistons. The valve
relief area. I'd say your valves have just been
kissing the top of your pistons. Not that bad
though. When I over revved a 2.7t motor
the tops of the pistons looked like swiss cheese.

Looking closer you will see that damaged area is near valve relief area.On intake valves.

[Thuppu]

BTW pop, for how long have you been running on e85? I'm just thinking of the sooth/carbon build on your pistons... there shouldn't bee any with e85. Does the engine burn oil?

With e85 it is quite easy to tune the timing over the MBT limit without any knock. The cylinder pressure can destroy the engine before you can register knock. Also the carbon build on your pistons can act like a spark plug and you will get pre-ignition(also too warm spark plugs are bad), and too agressive timing will do it worse. It's difficult to tune full potential of e85 without a brake dyno, because on road it's really hard to tell when the engine stops to make power(whitch is the timing limit) or starting to drop power.

[quattrostyle]

Also no honing marks?

That's what I was thinking as well, cylinder walls seem too smooth?

[popdemonic]

Thomas,
the reason i popped up the head due to the engine is burning some oil when start up.i guess the valve guides are shot or
the oil from the breather issue i been posting right here for a numerous times.the carbon deposits on the top of pistons is motor oil indeed.
i've been running on E85 for nearly 4 years.For some reasons that coming into my mind 1.last 2 weeks on the way home i couldn't find
E85 at the gas stations so i needed to fill it with E20 2.the ignition table is way too aggressive.this time i will be hundred times more careful
on playing with Ignition timing(Lesson learn).I will need to pay for a dyno tuning.on road tuning,we couldn't find any free roads to do the log
files tuning in Bangkok ,Thailand.we are infamous one of the high traffic in the world.Any guidelines on playing around with igniton tuning Thomas?
Thanks,
pop

[popdemonic]

Patrick,
you meant the crosshatches on the walls?

[popdemonic]

some updated!
got all the pistons out today.I'm checking for some any damages.Fortunately,the rest of the parts is fine.Only a light scored cylinder #3
i feel some lightly groove at the bottom of the scored mark line.uptop and middle is smooth.i'm thinking to leave it there and use it.
2 weeks ago all compression readings was 160psi.might be considering another AAN and preparing for swap when the right time has come.
the bearings on 5rods seems perfect.none of any scratches,seems they're still have plenty to go.








my sump baffle





It's superman's car.not sure some graphiti experts at the service shop did it.lol

[quattrostyle]

Yes, on the pics it looks like a mirror, don't know if that's just the picture though?
Also it won't explain the marks on the pistons but maybe explain why the pistons are kinda black?