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

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.

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.

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.

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

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. :icon10:

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.

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.

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.

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.

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

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

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

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.

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?

It is a Chinese copy of this Honda engine, they refer to it commonly as a CB250.
http://www.hondatest.com/wp-content/...nda-2013-_.jpg
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

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

Quote:

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Originally Posted by magma

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

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Well... Not necessarily.

http://www.youtube.com/watch?v=VQWCHGv3VFQ

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!!!!!

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.

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

Quote:

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Originally Posted by Zorge

Well... Not necessarily.

http://www.youtube.com/watch?v=VQWCHGv3VFQ

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That's a good engine...
http://www.bikeexif.com/wp-content/u...rs_tracker.jpg

Thanks for the link MJH. Can I use this piston without a new cam? Some people say using one without a performance cam can lead to a power loss. Any thoughts?

you want more compression? trust me. do it in the 3 following steps.
1.you can remove 1 mm from the head cylinder.
2.you can use a thick piston that might cost a lot.
3.you can use a big bore piston that not only increase the compression but also increase the displacement.(ask me if you don't know why it happens!)

actually compression ratio tells about how many units of air and fuel had compressed into one unit. for example 10:1 compression ratio means that 10 units of air have been compressed into one unit.
more compression means more power...when the mixture is more compressed it means that you have a more powerful and effective combustion.
but notice that high compression can cause a problem i call it "kick". when the gasses are compressed the temperature raises and in a high temperature the mixture will ignite before the spark plugs.
this can cause serious problems in engine and is known as a kick sound from the engine.
to solve the problem for high compression engines a fuel with higher octane should be used that can stand against high pressures.

Thanks again for more comments. Magma, I don't want a big bore kit as I would need case machining, crank shaft etc and would add up to too much money. It's either going to be a head shave or high comp piston. Is a cam upgrade required for either of these or will I get more power than the way it is now without it whilst not damaging the engine?

Just for anyone else out there thinking of doing the same thing as me I got some crf230 stock piston measurements from a dude off thumpertalk and the comp height is different by 1.5-2mm. The crf piston's height is less than mine so I'll have to go with Magma's advice and get the head shaved.

Don't touch the head - shave cylinder.

I already made my recommendations, you cant ask me to imagine I am cheap when I am not.
http://www.bbrmotorsports.com/produc...d=411-HCF-2301

Zorge, can you tell me why I should do the cylinder and not the head please? MJH, what do you mean?

trust me....don't shave the cylinder. you will decrease the displacement and the compression both....just do the head cylinder....JUST!