Mystery Piston Damage / Marks

[londonboards]

Pistons from a GS1150 / GSX1100. Look to be in good shape all round.

After de-carbonising them I found these weird marks:









I'm pretty sure I can still use them but I'm just curious to know how this kind of damage can occur.

Greetings

[JEEPRUSTY]

looks like heat dis that

[JamesWhut?]

What do the corresponding head surfaces and valves look like?

[hampshirehog]

Take a look at the link below. Possibly page 44.

http://www.boosttown.com/engine/piston_damage.pdf

[Chris G]

Take a look at the link below. Possibly page 44.

http://www.boosttown.com/engine/piston_damage.pdf

Thats now saved in my favourites, excellent site.

[londonboards]

hampshire - wow thanks for that link. Pretty comprehensive review of piston damage. Yes I would guess from that it was caused by knocking, pre-ignition, pinking which actually erodes the piston like that.

Thank you.

Greetings

[Nessism]

Hey, I was going to say detonation, and I didn't even read that link. The question is why was it knocking? Best make sure the mixture is correct, and retard the timing if necessary.

[rapidray]

Ed got it, detonation!
Ray.

[Nessism]

Years ago a friend and I rebuilt a hot rod SL100 Honda for another friend. Reason for the rebuild was a hole in the piston caused by detonation. Running lean and flogged mercilessly.

[tatu]

It seems an odd place to be getting a hotspot for that erosion to occur, all the pistons that I have detonated have been directly under the spark plug it, possibly it was caused by a carbon build up of carbon getting hot and causing the pinking. Was there carbon on the head at his place? I'm guessing that it comes from sustained heating.
Are they all like this or similar and was this from one'v your tuned, modified engines?

[Brendan W]

Last time I saw something like that a spark plug nose insulator had broken up and rattled around the cylinder for a few seconds before being spat out.

[JamesWhut?]

That would have been my first guess.

[londonboards]

tatu - it was from the motor you helped me pull apart. Yes the pistons were dirty as were the valves and combustion chamber and yes at some stage this motor had been breathed on with hot cams. But the pistons and liners had been replaced after the clutch explosion so they were more recently installed. Carbon in that area could have caused a hot spot and pre-detonation. This was the only one like it and to be fair the piston and the others are in good condition apart from this.

Greetings

[reliant_turbo]

coming from a turbo motor background, i was going to say detonation as well.

it is on the exhaust valve side so if the valves are hanging open a touch (aka not cooling by transferring against the seats) they could be the hotspot and if that cyl is a bit rich, there could be a pocket of unburnt fuel around that area to explode when ignited by the exhaust valves.

Brian

[Carter Turk]

London, any idea on the brand of piston? Any letters stamped on the underside?