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Melting Hole Through Piston

11K views 18 replies 9 participants last post by  MonkeyWrench 
#1 · (Edited)
Hey guys, so early in the week I had the opportunity to do a high speed run with my 2003 zx6r on a closed down private airport. From 1st to 6th I was wide open and all was going good until about 146 (gps Indicated) I noticed the bike slowing down and sound horrible with a terrible miss. Once I got pulled off the runway, I looked at my exhaust to notice it was blowing oil and tons of smoke! I trucked the bike home and immediately tore the motor apart to find out I melted a nice hole the size of a pencil eraser on cylinder #1 as well as melting the plug.

obviously the bike went lean in that cylinder, but why? I checked for any kind of cracks or leaks on the rubber intake boot that would cause it to be sucking more air that it should be, and all looked good. One thing I did notice on the inspection is that I had 2 very slightly bent intake valves on that cylinder, and I mean just very slightly bent to the point that it would still had enough of a seal to hold liquid for a while before seeping all out.

Anyone ever have this happen to them before or have any idea what could have happened to cause this damage? All my other cylinders looked perfect! The plugs were a nice golden brown as they should be.... except for cylinder #1 :unhappy:

The only thing I can think it could be at this point is my injector?

I hope someone can give me some insight to this problem.
 

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#6 ·
Don't rule out a bad casting/forging of the piston. It CAN happen. It almost looks like it blew out from the bottom up. Strange shit happens at 16K rpm!!
 
#8 ·
I don't at all suspect it was a bad piston. After all the bike had 25,000 on it with no problems and all the pistons look brand new with absolutely ZERO wear on the skirts. I was very impressed and how good the internals looked for the abuse the bike has gone through in 25,000 miles.... guess that's what good oil does for ya!
 
#11 ·
Why are you discounting the bent valves? It seems to me you found the problem but your not accepting your findings? You do realize how little time there is to close the valves at 15k rpms? Even a very slight delay will leave them essentially wide open at those speeds.

You should also check your valve springs. You may find that they are worn out. That may be the cause of the bent valves.

But with obvious mechanical problems I would not focus on the fueling so much.
 
#12 ·
Why are you discounting the bent valves? It seems to me you found the problem but your not accepting your findings?
Bent valves are one problem, but it's not obvious how that would lead to this situation. If anything, they would reduce compression in the cylinder causing it to burn rich. What could have happened is that the rich mixture could have caused carbon deposits on the piston, which in turn became a hot spot and caused repeated preignition. It's just a speculation though. I think it's very much worthwhile to understand the exact causes of this, if for no other reason, then at least to make sure this problem doesn't reoccur after the engine is fixed.

There is also another question: why are the valves bent. Were they bent before the piston damage, or did that happen as a part of the same event, etc.
 
#18 ·
heat could.mean fuel being lit up as mix was sucked in to the cylinder and heat the valves?
 
#19 · (Edited)
I am doing my first Texas Mile run next month and one thing i have been told by friends who have run there, as well as the place i got the nitrous kit, and my dyno tuner is that for wide open runs the bike has to be tuned REALLY rich because of heat and as a result of heat, detonation. Actually a friend who runs his busa there said and i quote "you have to tune really rich since wide open runs tend to burn a hole in the piston".

I suspect that was your problem. Holed pistons are a result of excessive detonation as evidenced by the pics you posted. See how the piston tops are smooth anymore and you have spots on the piston tops that are light colored. Thats what happens with detonation. Its all 4 pistons from the look of it and not just the holed one which would mean it isnt a fuel problem to that one cylinder but excessive heat in all 4 combustion chambers.
 
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