Krossipoiss

Member
Oct 26, 2008
93
0
Just brought 04' kx250f and i'm planning a full rebuilt on engine.
Searched for piston on ebay and i saw many different ala "14.2 -1, 13.5:1, 12.6:1 etc"
So whats the difference and what to buy ?
 

_JOE_

~SPONSOR~
May 10, 2007
4,697
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Compression ratio. Stock should be 12.6:1. The others are higher compression models that may require race fuel to run. My old crf ran fine on pump gas at 13.5:1 compression. 14.2:1 would most certainly need better fuel. Watch the valvetrain closely in that bike, I'm pretty sure they're notorious for grenading.
 

Krossipoiss

Member
Oct 26, 2008
93
0
Thanks.
So if i use "euro 98 pump gas" i shall use 12.*:* or 13.*:* not higher ?
And about valvetrain.I'm not excellent in english.Did u meant that valves could be near to death ? How to i identify it ?
Sorry for my nooby questions, but my first 4stroker and i want to make all by myself.
 

_JOE_

~SPONSOR~
May 10, 2007
4,697
3
You need to pay very close attention to the clearance between the cam and valve buckets. When the clearances tighten it is a sign there is wear going on. Once they start to wear they tend to go quickly. Keeping the air coming into the engine clean is critical, small dust particles can damage the valve coating and/or seat.

I'm not familiar with euro fuel grading but premium pump fuel from should work fine with compression in the low 13s.
 
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