tuning a 2002 CR250

D36-108A

Subscriber
Joined
Dec 3, 2002
Messages
367
Likes
0
#1
I'll be rebuilding my 02 CR250 soon and I'd like to tune it. What are the ideal specs for piston protrusion and squish clearance? I'm assuming it has grossly excessive squish clearance that is easily remedied simply by milling the head. Is there a standard "just shave X mm off the head" for more compression at high altitude? Race gas is not a problem.
 
Joined
Nov 17, 2005
Messages
55
Likes
0
#3
1st thing everyone on here is going to say is "did you buy a service manual?". This will answer all your questions on specifications such as those. Sorry I did not ask your specific question though.
 

IndyMX

Crash Test Dummy
Joined
Jul 18, 2006
Messages
5,546
Likes
1
Location
Amo, IN
#4
Hmmm my manual doesn't get into advanced subjects like squish bands and how much to mill in order to change the compression..

Seems like something someone like Eric or Rich would probably know about.
 

D36-108A

Subscriber
Joined
Dec 3, 2002
Messages
367
Likes
0
#5
Hell my TZ250 manual barely goes into the subject.

I'm hoping I can just mill the head to lower the combustion chamber volume and decrease the squish band clearance.
 

mtk

Member
Joined
Jun 9, 2004
Messages
1,409
Likes
0
#6
The information you're asking for is generally only found by lots of very expensive trial-and-error testing. In other words, the folks that have that knowledge don't give it away for free. You can either pay a professional tuner to apply his hard-earned knowledge or get busy creating a collection of junk parts learning it yourself. You're highly unlikely to find someone giving that info away.
 

D36-108A

Subscriber
Joined
Dec 3, 2002
Messages
367
Likes
0
#7
No kidding? Weird. On roadrace forums people are happy to tell you, "Oh yeah, that year likes X positive piston protrusion and Y squish clearance with Z volume. Just don't advance your ignition beyond so-and-so." But I guess nobody is trying to make a buck tuning 125/250GP bikes, compared to MX bikes.

But I did find out via Google that I should aim for under 1.4mm squish clearance. I guess that's a start.
 

IndyMX

Crash Test Dummy
Joined
Jul 18, 2006
Messages
5,546
Likes
1
Location
Amo, IN
#8
I have seen threads addressing issues like this before on here, I think mtk is overstating it quite a bit..
 
Joined
Oct 19, 2006
Messages
8,130
Likes
2
Location
Merrillville,Indiana
#9
I'm assuming it has grossly excessive squish clearance that is easily remedied simply by milling the head. That is a mistake that a lot of people make! I prefer leaving things like that to thee professional,and I will not be counted as a fool with tools and a big barrel of scrap heads and cylinders. You could buy a 2 stroke software simulation,program all the specs and see for yourself! I seen an engine a couple months ago and some bozo removed the squish clearance all together,all it had was the gasket!!! Yes the piston did hit once in a while???? http://www.dirtrider.net/motosource/egorr/ericgorr.html, http://tsrsoftware.com/compress.htm, And then you have the out there,that may or may not work in an mx applications!,http://pesn.com/2005/10/13/9600187_Design_to_Improve_Turbulence_in_Combustion_Chambers,
 
Joined
Oct 21, 2002
Messages
285
Likes
0
#10
just for the record here i totally aggree with foxforks, unless you are prepared for the trial (and error..) then you need a tuners experience for jobs like this. BUT having said that i wondered this same thing a while back and after searching through countless threads i found a post from a guy with a 02' cr250 who mentioned the low static compression ratio and said that he had milled 10 thou off the head and it made a big difference to the low end power, with no bad side affects. i was thinking about doing this myself but never went there.
if you try it, update this post and let us know how you got on.
fowardmotion racing or RB designs both do head mods with good results im told. they would know how much to take off your head and reshape squish etc..
good luck.