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

[gusmanxtr]

Hi peeps, would anyone know if I would gain anything by putting an 11.1 piston in my currently 9.0.1 cb250 air cooled ohc engine. I hear talk of only using these when you change the cam for a performance one but wouldn't more compression give it more power anyway? The piston I want to try is a crf230 piston. The engines have the same bore and stroke. Any good advice will be greatly appreciated. If you can give reasons to your advice so I can understand that will be cool to.
Thanks, Gus.

[Zorge]

Generic advice - pay attention on piston's compression height, shape of the crown and valve cutouts, even on overall piston height and it's skirt.

[gusmanxtr]

Thanks for your reply man. I have measurements from a wiseco dealer in Australia, the comp height seems to be 2mm less than my piston(that's without the built-up stuff on top of the piston). Can you tell me what the skirts are and what difference they may make?

Thanks, Gus.

[gusmanxtr]

Also, I didn't say it's a high comp piston I want to try just incase you didn't already guess.
Gus.

[Zorge]

I'm glad you mentioned this, because I think you're interested in anti tuning - you want your motorcycle to run slower, consume more fuel, and sound like an old lawn mower.

Since my English is very poor, I would recommend you use it to Google and find some information about the piston skirt, shorter or longer skirts, pros and cons. If I try to explain it to you in English, there is a serious chance that you're gonna push your motorcycle into a ditch and buy a bicycle.

Now, we're talking purely theoretical: lesser compression height means that compression will be lower, consequently, power will be reduced, if compared with the stock engine. On the other hand, if the piston crown is more convex (again, if you compare to the stock engine's piston), it's possible that you'll get with it higher compression. And then there is the question of the position of the valve cutouts, and whether they correspond to your engine's head and angle of the valve stems. And that's just the start.

Or, you could skip all the concerns, install new piston, and check it in practice.

[magma]

hey guys
i dont think that would be a nice idea. cb250 is paternal twin. am i right? crf 230 has got 63.5mm bore....seems to be to much for your bike. you can use a cg 150 piston. then you will have nearly 280cc displacement.

[Zorge]

I admit - I don't know what mean "11.1 piston", or "9.0.1", but I remembered one thing - Aussie mentioned same bore and stroke, so I thought he's talking about early '80s single cylinder quarter-of-a-liter CBs.

[gusmanxtr]

The chinese cb250 engine is actually a 223cc engine, the same as the crf230 engine. The top end looks the same when comparing engine diagrams. For some crazy reason they stamp 250cc on the cylinder when it isn't. The bore is 65.5mm and stroke is 66.2mm, the same as the crf230. There are different cb250 engines made in china with different bore sizes etc but mine is the size I just said.

[MJH]

You can find those kits fairly easy BBR has one and it adds 10cc and can include a performance cam and springs.
http://www.bbrmotorsports.com/Products/Products.aspx


This is not good forum for the topic, better would be a CRF forum.


http://www.4strokes.com/forums/topic.asp?TOPIC_ID=14171

[zhu]

best piston to use is wiseco as its forged and you can get whatever comp ratio you want
raising the comp will increase power but it will make the bike more fussy about fuel
11:1 will be ok using 98 which i assume you can get in oz
you need to measure the old piston and check all dimensions specially the deck height (pin to crown)
and make sure the valve to piston clearance is at least 1mm
wiseco pistons are spendy but so beautiful you may not want to put it in the engine

4816M06550

$211.05

65.50mm

STD

Compression Ratio - Actual: 11:1 Cylinders: 1 Displacement: 223cc Stroke: 66.20mm