Maintenance & Technical > KX500 Original

Time To Tear It Appart

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Just an old rider:
 Here is some more pics of pistion .. I don't see where it is broken  ??? 

Friar-Tuck:

  Yikes.. :| 
 
  Like BDI has eluded to, if you check the recommended maintenance schedule on motocross bikes, I don't think 80% of us could afford to run them..
   Pistons and rings according to the owners manual of my 2000 is inspect every 3 races and replace every 5 races..  how many hours is that 15-20 including practice?   
 
      There is a thread on the piston window mod by Stewart you could apply to another or overbore piston if need be.
   There are several options at this point and maybe some of the other guys will chime in.

 If you are considering re-plating, you may be able to go back to stock, however there is a limit to how much plating can be applied.     Oversize, re-plate or oversize sleeve,
  or stock dia. and sleeve.   
      Well, Things can only get better now!
    Best of Luck...
Tuck\o/

Just an old rider:
 :evil:  Isnt't that how it works ... Ride it till it blows then do it again ....     :evil:

Larry Wiechman:

--- Quote from: Just an old rider on December 31, 2009, 10:19:04 AM --- :evil:  Isnt't that how it works ... Ride it till it blows then do it again ....     :evil:

--- End quote ---

 The classic 2-Stroke rebuild, EVERY MOVING PART!
 
Larry

DoldGuy:
Old Rider,

If you go for an oversize piston be cautious of using the window mod on the piston as I know on the 88.5 piston the inside of the piston has been lightned and the walls of the piston are quite thinner & will not support the window mod, don't know the thickness of the in between over sized pistons (anybody?). The plating companies can work wonders & don't think yours would be a problem to have replated on a standard bore.

I was riding with a buddy years ago & had a similar problem, what had happened was the head gasket started to leak into the bore washing the cylinder down & leaving no fuel between the piston & bore and left the piston like yours. Check your head & cylinder surface to confirm a good sealing surface. Just something else to check to be safe.

Tuck, after I purcashed my 250F Yammie in 01, I was going over the "Recommended" Maint Schedule, and if memory serves me, it said to replace the valves every 20 hours. OUCH! Back then the Ti valves were almost $700 /set.

DoldGuy

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