Kx500 piston scattered

[dfr136]

Any idea what would cause a 500 piston to scatter like this? Fresh rebuild. New 87mm wiseco, new crank bearings. Stock jetting. 32:1 with 100 octane pump gas. Cylinder was in great shape when it went back together. This happened first ride after the rebuild. Not sure what to do at this point. Is the bottom junk now? Any insight would help as I haven’t a clue what would cause this.

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[Sandblaster]

Pull the head gasket off and post a pic of the top of the cylinder.

[dfr136]

There’s still a little yamabond on it.

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I hope this is fixable

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[Sandblaster]

Were you having a head gasket issue?
That is classic of a head gasket failure and I'm guessing that you were having a problem with it, hence the yamabond?

[dfr136]

It had never ran before. I yamabond it just to be safe as I’ve heard the 500 can have head gasket issues. I don’t know if I was having head gasket issues because it only ran for about a half hour or less and I had no leaks from the outside. Plug looked great after he first initial start and break in ride. What I had noticed was a almost detonating type of sound, I have never had a bike ping but I heard this mettalic sound only under load. I thought it could of been just the way the 500 sounded. Thinking I was wrong on that. I noticed the sound from the first second I rode it.


Would a head gasket/ coolant issue cause the bike to detonate? I’m going to be calling millennium today to see if they can weld that part of the cylinder, and re coat it and deck the gasket surface. I would like to just try and figure out what happened before I rebuild the bike again.

[Sandblaster]

Yes, if your coolant is leaking onto a hot piston it will make all sorts of racket..
I'm not sure if Millennium could weld that or not, although they have fixed some pretty bad cylinders for me over the years.
If they can't weld it, they could likely sleeve it for you.
If I was doing the work, regardless if it can be welded or sleeved, I would deck the cylinder and cut the head to insure that they are completely flat.
Yes, you have to remove the studs and replace them but it's well worth it.

Give Jason a call, I know he'll be happy to help you out.