1999 cr250 piston is this normal!!?

[Big80Wr450f]

Hey guys, just picked up a 1999 cr250. I'm going through the top end and came across the piston and cylinder. The cylinder looks immaculate with criss hatches still but the piston looks like this. Can you guys tell me if this is normal

[ScrewMx_Hd]

no

maybe piston catching on something in cylinder

[Big80Wr450f]

no
maybe piston catching on something in cylinder

Like what? I don't see any sign in the cylinder of my piston catching on anything? Can it be that the guy I bought it from was running a fuel mixture of not enough oil ?

[bourdeau]

That much look like it melt due to overheating. It's align with the exhaust port. That's all make sens. Check your jetting for to make sur it is not too lean. Also what premix ratio did you run? And check you cylinder to make sure he is in good condition before put a new piston in it

[Big80Wr450f]

That much look like it melt due to overheating. It's align with the exhaust port. That's all make sens. Check your jetting for to make sur it is not too lean. Also what premix ratio did you run? And check you cylinder to make sure he is in good condition before put a new piston in it

Yeah I looked in the cylinder and it looks really good still. Is it safe to run the piston like that? And the guy I bought it off of said he ran it at 40:1.

[bourdeau]

40:1 is good mix but for sure I would not run that piston again, put a new one. And check the jetting and check if the intake seal good, if the intake leak, the bike will run leaner for sure.

[Big80Wr450f]

40:1 is good mix but for sure I would not run that piston again, put a new one. And check the jetting and check if the intake seal good, if the intake leak, the bike will run leaner for sure.

How would I know which exact piston size to run?

[bourdeau]

Check if it's a oem piston. Oem piston a made by ART and it's suppose to be stamp somewhere under the piston like this... just to look at it, im pretty sure he is an oem. But the best thing to do is to measure the cylinder and check the tolerence referring in the owners manual.

[bourdeau]

[mxsteve1968]

Seen this a 1000 times.. The piston has been ran past its service life, along with poor filter maintenance and wrong oil / mixture, revving it cold ETC. Get the cylinder measured and an wiseco piston kit and go riding

[Big80Wr450f]

Seen this a 1000 times.. The piston has been ran past its service life, along with poor filter maintenance and wrong oil / mixture, revving it cold ETC. Get the cylinder measured and an wiseco piston kit and go riding

What do you think of my cylinder? I measured it. it measures up to OEM spec 65mm and the cylinder has an A stamp. Would I be good by just running a new size A or B piston?

[Big80Wr450f]

I read the caliper wrong. It's 66. Something

[ohiodrz400sm]

The .XX something is what's important

[Big80Wr450f]

The .XX something is what's important

I don't have a expensive caliper gauge.

[mxsteve1968]

It should be around 66.40 within tents of a mm. cylinder looks pretty good. You wont find an a piston so you will run the b piston, its what we all do now and its just fine. I suggest running the wiseco forged piston kit and follow the directions that come with it. The wiseco rings only work with the wiseco piston and are usually directional. They will have a dot or a mark at the ring gap, these marks will face up on the piston. If there are no marks you can install them either way. don't for get to measure ring end gap. The end gap should be no less than .04 thous per inch of cylinder bore width. refer to your manual on how to do this.

[Big80Wr450f]

It should be around 66.40 within tents of a mm. cylinder looks pretty good. You wont find an a piston so you will run the b piston, its what we all do now and its just fine. I suggest running the wiseco forged piston kit and follow the directions that come with it. The wiseco rings only work with the wiseco piston and are usually directional. They will have a dot or a mark at the ring gap, these marks will face up on the piston. If there are no marks you can install them either way. don't for get to measure ring end gap. The end gap should be no less than .04 thous per inch of cylinder bore width. refer to your manual on how to do this.

Thank you!!

[Pigsfly]

Go for a woosner piston kit buddy ,one of the best forged pistons you can get,

cylinder looks fine, but  I would take it to a motorcycle shop and haven't measured correctly  for the correct size of piston. 

 

as Steve said about maintenance is the key to longevity. Air Filter maintenance is a must.

check the Reeds also 

 

i have a 99 also , engines are built proof if you look after them .remember you only get around 40h per top end rebuild,past that you're asking for trouble. 

[bourdeau]

That's will look like a thread about what oil you should run, everybody will say run what I run, it's the best. Lol wiseco, vertex, wossner, they are all good product, you will never have issue with it. If you have access to oem parts, I suggest you to buy Honda stuff. Really not more expensive, you are sure that the best for the bike. But that dont come in a kit, you have to order every single parts you need, that's why people go with complete aftermarket rebuilt kit, it's more simple. Just buy anything you want, they all good[emoji106]. But keep in mind that forged piston are way louder when the bike run, it give a rattle that is normal, and you should wait more for the engine warm up before go riding.