What causes this?

[evo550]

Does the ring end gap run on the bridge between transfer and boost ports? If it does ring end gap is much more critical than running through the middle of the boost port.

The ring end gap is behind the inlet port..If the arrow on the top of the piston is 12 o'clock, the top ring gap is at about 20min past and the bottom ring is about 20 min to the hour.
As far as I know everything is standard, I think your on the money with it getting hot, especially looking at the photo to the valve on the left, starting on the outside it looks nice and tan, but it changes colour the closer you get to the exhaust bridge, with the tip looking like it's got white hot.
Why is it getting so hot though?
My question is, Could the powervalve thats not operating and remains closed cause heat build up at higher revs through resticting gas flow?

The end gaps run on the bridges between ports. There is to much black soot carbon in there for any jetting ignition issues, head gasket would fail if there was water problems.
You would know if the PV was not opening they just struggle to rev and generaly very flat. The exhaust bridge has aluminium smeared all over it.
There's my $0.02 not enough end gap/to little clearnce/no relief is rubbing on the bridge and bulging  and heating the piston. Is the ring stuck in the groove at the front of the piston.

The end gaps are behind the inlet port shown in KB17's 2nd scan, illistration "E" and point 4.
I was originally unaware of the meltdown, as I was  investigating a hunch that the PV's wern't operating when I stumbled across it. Thread in Honda section "HPP exnaust valves"
Although posssible, I would like to give them the benifit of the doubt that Serco would not make the same mistake twice...so I'm looking for another common denominator, to why it would happen twice to new cylinders/pistons, and the PV's not opening is really the only other possible cause.
Instead of a resleeve can these old iron bores be replaced with nickasil?

[Freakshow]

Sand out that aluminium off the bore  and whack the lot back to gether.  its now found its own clearance

[tmman]

don't forget just add a new ring or 2 freaky!!!

[evo550]

Sand out that aluminium off the bore  and whack the lot back to gether.  its now found its own clearance

don't forget just add a new ring or 2 freaky!!!

Does that mean I can still use the old piston ??

[Lozza]

You can nicasil over cast iron no problems. You get the aluminium off with hydrochloric acid and a cotton bud. The piston will have more answers.  Hondausualy put the end gaps on the bridges.

[evo550]

You can nicasil over cast iron no problems. You get the aluminium off with hydrochloric acid and a cotton bud. The piston will have more answers.  Hondausualy put the end gaps on the bridges.

Pistons a little worse for wear....top ring is seized in,will post pics tonight.

[OverTheHill]

My 2 cents worth for the evening is, i see lots of talk about ring end gap [gaps] on the bridge. I imagine you mean a bridge on the inlet side or bridge between transfers or somewhere & "not" the exhaust bridge that the main subjects about?. Ony reason i'm saying this is [is the piston in back to front] or are they a "reed holes in the piston" type which couldn't be done wrong, [or a case reed inlet? i.e. piston without reed holes], not familiar with the honda [last one i had was the first elsinore]--long story. Thanks. ps, actually did recently see a reed piston in back to front, was a jack up someone was doing using reed piston in a cylinder with rotary valve, was a good fix as pistons weren't available, went well when he put it back correct way round. Sorry--carry on.

[evo550]

pic of piston

It was still running in this condition, I only stumbled across it while checking to see if powervalves where working....which they are not...but I'll leave that for another thread.

[OverTheHill]

sorry, me not reading. I see where end gap are.

[Simo63]

pic of piston

It was still running in this condition, I only stumbled across it while checking to see if powervalves where working....which they are not...but I'll leave that for another thread.

Surely if the power valve is not working that will meanit's closed or half closed and that in turn would lead to excessive heat build up in the exhaust port and on that exhaust port bridge?

Maybe your problem is related to the power valve.

[Lozza]

The piston looks to have no issue with the bridge or you would see a lot of polishing over the oil holes. Incorrect piston to bore clearnce would show evidence all over the piston.
PV not opening might have contributed with higher dynamic comp than the fuel can handle. Piston gets hot, traps the ring rubs on bore end of.

[GMC]

Can’t see how the power valve can cause heat build up. All it does is lower and raise the exhaust port.
Trailbike engines don’t get hot because they have low exhaust ports and peaky engines don’t get hot because they have high exhaust ports.

One thing that comes to mind though is that it’s on a large oversize and some power valves can open into the piston area once they are bored oversize.
Have you checked that the power valves don’t protrude into the chamber?
Are there any marks on the tips of the power valves?

[matcho mick]

Lozza the piston striations don't match up with the rings  ,especially those 2 "cuts" on the r/h side of piston above top ring(left side of picture),& go back to 1st picture of bore,the hone marks are gone from above the bridge,again the rings don't match to that amount of difference?,is something else going on,is b/end trying to tell us something?,or did Evo not cleanup the previous lot of damage,& thats come back to bite?,just seems a lot more of piston smear damage,& the rings suffered less?,

[evo550]

Can’t see how the power valve can cause heat build up. All it does is lower and raise the exhaust port.
Trailbike engines don’t get hot because they have low exhaust ports and peaky engines don’t get hot because they have high exhaust ports.

One thing that comes to mind though is that it’s on a large oversize and some power valves can open into the piston area once they are bored oversize.
Have you checked that the power valves don’t protrude into the chamber?
Are there any marks on the tips of the power valves?

The valves had to be done at the same time as rebore to ensure clearance, you can sort of an idea in the first pic.

Lozza the piston striations don't match up with the rings  ,especially those 2 "cuts" on the r/h side of piston above top ring(left side of picture),& go back to 1st picture of bore,the hone marks are gone from above the bridge,again the rings don't match to that amount of difference?,is something else going on,is b/end trying to tell us something?,or did Evo not cleanup the previous lot of damage,& thats come back to bite?,just seems a lot more of piston smear damage,& the rings suffered less?,

That is some serious detective work. The first pic is of the cylinder after first seizure (I don't have old piston), second pic of piston after second failure, I can get one of the cylinder to match piston pic.
It was given a rebore after first mishap.Pic below.

[matcho mick]

errr ok,1st piccie of seizure in bore dosen't belong to the damaged piston shown?,(that all makes sense now  ),ok,we now need to see  lastest bores seizure damage,