Analyze my piston

[Stusmoke]

The orange crap on the crown looks like ring blowby, but its on a certain area of the piston.

It called a wash pattern, hotter areas of the piston cause the oil 'char' and stick to the piston , no charring no heat on the piston.

Then I retract my statement. Thank you

[Stusmoke]

The orange crap on the crown looks like ring blowby, but its on a certain area of the piston.

It called a wash pattern, hotter areas of the piston cause the oil 'char' and stick to the piston , no charring no heat on the piston.

Hopefully that will be your answer and its a short adventure. The salt and pepper definitely looks like debris

[2T Institute]

Pock marks are detonation. Detonation is from ineffective squish. The marks are not big enough to be foreign matter

[beaner]

I've never seen water cause this type of damage, but I can't see what else it might be. It looks too small for debris, and it's definitely not detonation. The wrist pin was a little tighter than normal coming out and there are some marks on it that I would associate with water getting between the pin and the piston, so I'm tending to believe it's water for now. The black and brown on top are perfectly normal.

[2T Institute]

The sandblasted timing edge of the piston indicates plenty of detonation. Wash pattern is far from normal. What squish gap and % is it running?

[beaner]

I'm certainly open to suggestions. This is the first time I've ever seen damage like this, and that's why I posted the pic. I still don't think the damage is by water, but it almost certainly saw some, and that would explain why it's so clean. I didn't say the pattern was normal, but that black and brown on the crown was.

The combustion chamber is stock.

[2T Institute]

Water ingress would crack a hot piston instantly, usualy between the timing edge and the ring gland. Have you measured the squish gap? What fuel was it running?

[cnrcpla]

Water ingress would crack a hot piston instantly, usualy between the timing edge and the ring gland.

Yeah. It happened to me once... If I can find the pic of the piston I will put it up.

[bearorso]

04 RM 125.
Wiseco piston has been in the bike for 3 years, but I was hurt and hardly rode it for 2 of them. I installed a new ring last spring, and raced it at 6 events this past season, and probably a dozen practice days.  I rode it hard and it ran flawlessly. The ring is like new, and well within spec. The piston looks like new with the exception of the specs (looks like salt and pepper) on the top, but mostly concentrated on the top OD where it looks and feels like it's been glass beaded.
None of the previous 3 pistons in there looked like this, and I have made no changes. There was no indication of dirt or dust in the intake (it's all removed) and nothing unusual on the plug.

Given this information, and if you've not got a deterioration of sealing components - water, air - and the time line of the bike having no use, I'd tend to think that it may well be a reflection of the crap that is being passed off as fuel, nowadays. The variations in my bikes' running, can be quite marked, be it in getting fuel from the same supplier / pumps (because ever more frequently, servos are just getting fuel from whoever they can), or when travelling.

It's the major reason I am considering going back to race fuel - the belief in / hope for consistency, and getting What I Pay For. Even AV gas is something I'm considering again - on a lightly stressed 500, it's good enough, and it's controlled enough still, I hope, to be consistent in it's chemistry. And it's a lot more affordable than race fuel.

[beaner]

Water ingress would crack a hot piston instantly, usualy between the timing edge and the ring gland. Have you measured the squish gap? What fuel was it running?

I don't think I would agree with that. I've put lot's of water through some of my race motors without any problems.
As I said before, it was the same 91 octane that I've always used, even from the same place. It's also the same fuel I used in my other bikes this past season.

I've been dealing with a machine shop for the last 20 or so years, to do the things I can't do in my own shop. They are engine builders, primarily, and build some of the better race motors locally. I had to stop in today, so I showed it to them. They said two things. That's preignition, not detonation, and whatever it was that caused it has either been fixed, or went away on it's own, because it's old damage (which I think is obvious).

[SachsGS]

I can't get over HOW CLEAN portions of the piston crown are, very strange.

[riffraff]

I can't get over HOW CLEAN portions of the piston crown are, very strange.

It is awfully clean, and the dark areas are on the intake side. What's the head look like?

[2T Institute]

Pre Ignition and detonation a 2 completely different things. There is no pre-ignition only detonation on that piston. Dets are recent and your squish still needs sorting. If the piston is hot, it will crack with very little water.

[TotalNZ]

While we're on the subject of piston analysis, check out these 2 rebuilds i've got on at the mo.
1's a 2000 YZ125 which was put together after it blew up with a needle roller still floating around inside.

That needles jammed in there tight.
The next is a 2006 KX250 thats leaned out and destroyed itself.

Would you believe that pistons 10 hours old apparently

[Stusmoke]

While we're on the subject of piston analysis, check out these 2 rebuilds i've got on at the mo.
1's a 2000 YZ125 which was put together after it blew up with a needle roller still floating around inside.

That needles jammed in there tight.
The next is a 2006 KX250 thats leaned out and destroyed itself.

Would you believe that pistons 10 hours old apparently

What. The. F**k. Someone neglected to do the wristpin bearing in the last dozen rebuilds. Thats messed. Hows old mates cylinder head and wall?