new here, just searching to see if there are any way to avoid scoring a 2 stroke.
i have a 1989 cr250r bike that im rebuilding the top end on. love the bike, wicked fast. riding it when loss of compression made the bike die. pulled it apart and found a deep non borable score so im going to have a sleeve put in. the piston looks re-usable(wiseco) but im just going to buy a new one to avoid future conflict. is there any way to avoid scoring the cylinder over? i have stock rings for a cr250r that wont fit my piston because the piston is wiseco. these stock rings are twice the size of the rings i pulled out of there. im assuming they should be about the same width. the ones i took out were just worn? the ring is what scored it after the end of the ring folded over and scraped up the cylinder wall. now i hear your supposed to rebuild your bike every 2 months or so of hard riding and 6 months of easy riding. is this true? but i dont think you have to literly rebuild it? just put in new rings, hone it, and a head gasket right? will putting new rings in before they get to this point pervent future scoring? thanks - jt.

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Usually about every 60 hours you are supposed to replace the piston on the bike due to them becoming brittle with wear. tho i've seen 10 year old bikes that have never had the pistons replaced and run just as good as new.

as far as scoring goes, make sure you warm the bike up well before you take off riding. make sure you have the correct sized piston for your bore and model. and just make sure you mix at a set ratio and jet accordingly.

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we just usually always "eye balled it" when mixing the oil and it was always either too rich or too lean and we didnt really let it warm up before riding.
probably why it scored, but im sure it had over 60 hours on it the rings were wore down to bearly anything. so at about 60 hours i should pull the cylinder check the piston for cracks or collapsed skirts and replace rings?
how long is a regular break-in period for a 2 stroke 250?

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2 heat cycles pretty much.

a Race motor like the CR was designed to run at 24:1. I run my yz at 40:1 running a synthetic oil.

Rings should be done every 30 hours or so to maintain peak performance, but no one really goes by that. I just replace the piston once a year (average about 250 hours + a season.) I use a wiseco piston and being forged it holds up longer then a stock OEM piston, you know when you need a new piston with a wiseco cause it will lose compression vs. breaking apart with fatigue.

For break-in start the bike and let it idle for about 2-5 min with the radiator cap off, allows the air pockets to work their way out of the coolent system, while doing that suit up and check over all the bolts and nuts on the motor, swingarm, and any other place you may have loosened. Then kill the motor, and fill the radiator back up.

let it cool all the way back down and re-check all bolts one more time. (Metal expands when it gets hot....)
Fire the bike up, let it sit for a couple min again. now take it off the stand and go ride, don't go wide open, but vary the throttle between 1/4 and 3/4 throttle to properly break in the rings. do that for 10 min or so, bring it back in and do a once over to make sure everything is working right. re-fill the tank and go have fun.

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by 24:1 ratio are you talking about oil to gas ratio mixure?

thanks for all the help, you've helped me understand 2 strokes better.
im used to 4 strokes, this is only my 3rd 2 stroke (first was a atc250r 3 wheeler 2nd was a ktm 250sx)
so im still learning what i can do to save a little $$ without blowing it up 5 times before i get it right.

ill probably buy a synthetic oil because im told it lubricates alot beter. should i run it at 40:1?
and without it being synthetic run it at 24:1? thanks - joel

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run what you're jetted for.... more oil = less gas = leaner mixture.

remember engines use fuel as well as the coolent to cool the motor....

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i have no idea what its jetted for. its got a wiseco piston, hot rod connecting rod, not sure if it has a aftermarket crank. has a racing trans(from what im told) and has a sneaker exhaust and i think a aftermarket expansion chamber as well as a twin air filter and it has the stock carb on it with boyesen power reeds. not sure if this helps any. the guy told me to mix 32:1

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i found out the expansion chamber is stock.

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if that's the bike in your picture. the pipe is not stock...

stock exhausts are steel and not nickel plated

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Buy yourself a mixing ratio cup for like $5 with the lid. Run Amsoil dominator at 40:1

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