blown up any ideas

[holeshot buddy]

riding my af500 last week in a race
locked up on second corner and spat me off
took it home pulled off barrel
piston disintergrated not even on rod
bore gouged conrod bent  (not happy)
engine about 30 hours old genuine piston
no power valve damage
looks like piston has  maybe cracked through gudgeon boss
and broke off a big piece which made a mess
no warning no noise no pinging
no coolant loss etc
anyone struck this i have been racing kx500s for 25 years
never done this
running at 32 to 1 motul 800
any ideas

[BDI]

I have seen stock cast KX500 pistons with cracks in the skirt at twenty hours. Cast pistons should be replaced once a season or every twenty hours as preventive maintenance. You got lucky the rod didn't come out the bottom of the cases.

[stewart]

cast dont last

[oic0]

Yikes, cast pistons really go to pieces don't they!

Differen't bike, but I broke a piston in an RD engine. It was a forged wiseco. The guy who ported it went to big on the intake and the piston could rock and hit the bottom of its skirt on the bottom of the intake. The piston broke the bottom of the sleeve and cylinder off. Didn't shatter though, it bent and had one crack at the base of the windows (it was a banshee piston with two big windows cut into it). Completely destroyed my cylinder though . I have much faith in the strength of wiseceo pistons now though! the stinkin thin windowed skirt broke my cylinder to pieces without sustaining all that much damage its self.
I was thinking about trying cast but not after seeing that!

[kxraptor]

Never seen a piston fragment  so much.

[kaw rider]

my did that because of over rev and down shift too fast.

[holeshot buddy]

yeah i didnt overrev it but anyway its stuffed now
any ideas on replacment piston brand
genuine or wiseco or
any ideas (stewart) or someone
all help appreciated


funny story took of exhaust first and looked inside
piston was sideways in bore

[The Flyin Hawaiian]

Same thing happened to my 500 with the previous owner. In his case, he just rode it into the ground. He wasnt much for maintenance. The piston shattered and a piece cracked the cases. A little over 2 grand later and he was back in service. The only thing that was original was the trans and clutch assy. He later seized it topped out on a dirt road. Luckily, the cylinder cleaned right up with some muratic acid. Im thinking about running a Wiseco after seeing those pics!

[stewart]

 only  ... wiseco...

[holeshot buddy]

thanks guys will keep you posted

rusty

[Uzi9mm]

I had a local shop do some suspension service recently.  While I was picking up my bike the owner claimed that he just did a topend on another guys KX500 and had problems with Wiseco.  The guy who owns the shop said, he installed a new piston from Wiseco and it made a lot of noise when the bike ran.  Supposedly, the shop tried 2 pistons from Wiseco with the same result.  So, the shop installed a piston from Kawasaki and the clatter was gone.  Now the shop claims the Wiseco pistons are no good for KX500s and recommends a stock piston for the KX500. 
Could Wiseco have a bad batch of pistons or did the shop screw somthin up?   

[BDI]

any ideas on replacment piston brand
genuine or wiseco or

Wiseco is genuine 

[tharden]

I would go with Wiseco.  I see a lot of cast pistons on the chainsaws I rebuild and they hold up well as long as the tolerances are with in specs.  The Destroyer of the cast piston is a worn skirt.  The chainsaw pistons I have dealt with are in the 125cc range, and can have over a thousand hours on them.  Fairly tough for a engine that is run at full throttle just about it's hole life at 9 grand.

[RoostDaddy]

Had this happen once with my old stroker motor.  Came to the conclusion that it was the wrist-pin bearing, as thats where the piston came apart.
With this motor I had to replace the wrist-pin bearing every 3 races, any more than that, you could feel the bearing coming apart.
Not saying this is your problem, just that this was the stress point in my old stroker.  ( now sitting in the basement )