Will a crf230 11.1 piston be ok in my cb250 engine?

[Zorge]

Compression ratio is, as I understand it, simply ratio between volume of combustion chamber at BDC and TDC. Compression is bit different thing.

[MJH]

I think his initial post is the cause of the confusion, the ratio at stock is 9:1, the big bore will raise it to 11:1 due to having a convex head.

[magma]

if you wanna increase the compression ratio the easiest way is two reduce the head cylinder height. just 1mm would be enough and effective. more compression can f..k up your piston or valves. can u possibly take a pic of your engine? i think cb250 is twin and the single engine is actually a cg250...am i right?

[MJH]

It is a Chinese copy of this Honda engine, they refer to it commonly as a CB250.

It's an OHC single 223cc 65.5mm X 66.2mm, the CB commonly refers to a OHC, the CG is a pushrod engine.

Here is link to an article that explains the relationship of boring and compression ratios.
http://www.badasscars.com/index.cfm/...362/prd362.htm

[magma]

i got that...your right
it's the crf230 engine. but it can be easily increased to 250 by a 70.mm bore pistooon like the ax-1 piston

[Zorge]

i think cb250 is twin and the single engine is actually a cg250...am i right?

Well... Not necessarily.

[gusmanxtr]

Hells bells guys thanks for all the replies this is awesome! MJH you hit the nail on the head with the engines. The top half of my engine which is called a cb250 is like that of the crf230, it is not a copy of a honda cb250 engine. The gearbox however is like one from a honda cb/cg 125. I don't want a big bore kit, I just want to get more compression/power. Some people say if I was to put a high comp piston in it without a performance cam there may be a loss of power. Can anyone knowledgeable confirm or deny this? Also, if I were to have the head shaved might this get me an equal amount of compression that I might get from putting a hi-comp piston in? If I went that way I wouldn't have to keep spending money on pistons. Please dudes, keep the comments coming!!!!!

[Zorge]

Piston swap you suggested, as I understand, won't be easy job, because your is for 2 valves (am I right?), with corresponding cut outs, and CRF's piston is... you can assume.

Anyway, my vote goes to Magma's way - shaving cylinder, if necessary, step by step.

[MJH]

This piston I believe claims to raise the compression to 10.5:1
http://www.wossnerpistons.com/produc...f-65-5-mm-bore


Here it is through a vendor in NZ…


http://www.motocrossparts.co.nz/moto...es.php?id=1874

[MJH]

Well... Not necessarily.

That's a good engine...