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2002 CR250 Info/help

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hey guys.

 

so, i want my squish cut as i finally ripped my 250 apart for the first time since i got it off of my buddy.

 

did the solder check on it and it came out to .069" What should the squish be set at? .40"?

 

also, i want to be able to run mid-grade. so increasing my cylinder head volume will be a must.. anyone have any idea on what i should set my head volum at?

 

info, opinions ect all welcome.

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rb deigns is where i would send it.  You could send him the head and the squish measurement, fuel preference and he does what he thinks is best. I personally build things to personal specs.

 

With squish, the smaller you go the more efficient the burn, that more power you make, but there are things to to take into account

 

  • rod stretch at high rpm
  • crank bearing play (happens at higher rpms)
  • carbon build up

 

anything over .050 and you are nose diving (in terms of leaving power on the table.  .040 is a good number if you keep the crank in spec. My 2005 rm250 was a no expense spared build by varner racing, squish was .039 give or take a thousandths . It was very very crisp and snappy. add to that high comp head mods so it only runs on race fuel and it was actually a bit to fast if i wasnt in shape or got sloppy.  Ive heard of full blown race motors being around .025 inch, and when you add in rod & bearing stretch at high rpm the piston is pretty much kissing the head on every stroke.

 

I would go for -040 - .045 inch. seems tobe small enough for a good burn in the head. but not so small it can't allow for a bit of carbon build up or rod stretch.

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X2 Good info

Rb did my KDX 220 head about 3 months ago and set it up for 100LL fuel. As a mechanist, I can say his work is top notice. Big improvement in low to mid power. I have never felt a 2 stroke motor pull this well low in the rpms as this KDX does now.

He took 3 cc out of the combustion chamber 24 -> 21. And closed the squish clearance from .095" to .060"

Stock compression was 11.92:1 now it is 13.9:1. Note I use the uncorrected comp method.

Psi before was 168 now 189.

As for the CR cc question. I am no expert. I took me 5 tries to get my cc, squish clearance, width, angle, and shape of the dome, the way I warned. Setting up a head takes a lot of R&D.

I set my clearance up as follow, .040"-.045" on a 250, 125 =.035" and 500=.050"

I would say you have to add back about 2cc to the combustion chamber after decking the head .029" to get to .040". If you want to run 89 octane. Have fun. I did on the cr. But as you can see when it came time for the KDX. It was smarter for me to send it to some one that had already done the leg work.

Edited by Kirkes

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