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CR250R Compression

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riding around the other day after buying a used 97 Cr250R, rode it around for about 3 hours...noticed the bike had died. figured it was the gas that ran out...kicked it again rode it for about 15 feet down a trail and it was overheated spraying white smoke from the front of the bike...somewhat loss of compression now, checked the top end which is fine. checked the radiator and there was no water...buddy thinks the water jacket may be cracked any ideas? its not seized because the piston moves up and down just fine, there is spark. carb is working fine its spraying fuel. everything seems to be fine. i'm about to take apart the jug, and left/right crank cases to check for damage...

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riding around the other day after buying a used 97 Cr250R, rode it around for about 3 hours...noticed the bike had died. figured it was the gas that ran out...kicked it again rode it for about 15 feet down a trail and it was overheated spraying white smoke from the front of the bike...somewhat loss of compression now, checked the top end which is fine. checked the radiator and there was no water...buddy thinks the water jacket may be cracked any ideas? its not seized because the piston moves up and down just fine, there is spark. carb is working fine its spraying fuel. everything seems to be fine. i'm about to take apart the jug, and left/right crank cases to check for damage...

A bike can still be 'blown up' due to piston/cylinder scoring and will not run or run very poorly.

Tear the top end down to see the damage. Because the piston goes up and down doesn't mean it's not scored along with the cylinder.

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right. i only took the top end off i have not torn down the whole entire jug yet. I will do that tomorrow and get back in here post whats going on. thanks. figured maybe the rings could have scored it because it got so hot and expanded.

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take off pipe and shine a light inside jug. use kicker to move piston.

what information will that provide me? or what am i looking for.

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what information will that provide me? or what am i looking for.

It's the lazy way to look at 1/4 of your top end. :busted:

I would just take it apart and look. You'll probably have to take it apart for some sort of failure.

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It's the lazy way to look at 1/4 of your top end. :busted:

I would just take it apart and look. You'll probably have to take it apart for some sort of failure.

Well at least the pipe is removed. Has to come off either way. :busted:

Purpose is to see if cylinder and/or piston are scored causing compression loss.

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Hey guys. I took apart the top end today. Found major scoring on the back of the piston and the inside back of the cylinder facing the air filter as if someone had been riding it with no air filter. ALSO found that since the overheat that the reed valves are completely melated and blocking air gas flow. Pretty sure with new seals rebore of cylinder new piston and new reed valves I should be good. I need to figure out why it overheated to begin with.

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that gasket surfaces like the 2 top end gaskets, i already have new ones if thats what you mean...i think since its a 97. the reason its scored so badly is prob because of its age...a little dirt overtime makes it past the air filter you know. the only scoring is facing the air filter end.

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yes, diagnose why it over heated. also when that much heat is generated its possible to damage bottom end bearings. most likely the con rod bearing. if your going to spend all that money on the top end i would do the bottom as well. Wiseco makes an affordable bottom end kit with every thing you need.

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i found that the previous owner had the brake res. empty. so its possible that he never had water/coolant in it to begin, me being an idiot didn't check before I rode. also found out that CR is notorious for allowing dirt through the carbs into the cylinder with a dirty air filter...that explains the minor scoring on the air filter side of the cylinder/piston.

- bcislandrider - Bottom end seems fine. I spun the wheel and shifted through all gears perfectly...

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there is a difference between seeming OK and being in good shape. any time an engine has seized or had major damage like yours its a good idea to do the bottom too. most bike shops would not just install a new top on a suspect bottom end. you may get some life out of it but chances are it will not last. if the bottom fails, all the new top end parts will be toast as well.

extreme heat is not good for bearings. the wiseco bottom end kit sells for around $169 includes crank, rod bearing, main bearings, main seals and gaskets.

i guessing that your top end job will cost about $500-$600 at least, whats another couple hundred for a complete rebuild and piece of mind.

Good luck!

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