cr 250 top end problems

[tracy harman]

i just put a new botom and top end in my 02 cr 250.also had the cylinder replated. i broke it in friday and sat raced it sunday in a mud race. during sunday practice before the race the bike ran out of gas. i went to my local tracks thursday night practice and rode for about 30 mins the bike kept making a funny noise so i brouhgt it in and couldnt find anything apperant so i took her back out about 5 min later the bike dies. i found out it had blown all the water out the overflow tube. when i tore it down the front 2 head bolts were loose im sure they were tight when i put it together. when i got the head off the exhaust side of piston was melted away like it had been runing lean. could the high temps have caused this type of piston failure or was it running lean? surely running out of fuel 1 time couldnt have did it. anyway im searching for some ideas i dont want to put it back and have it happen again . anybody who can help thanks

 

[bigred455]

Either 2 things I see, you already mentioned one the head gasket leak will definetly cause failure to the piston.Another is coolant mixing in the combustion chamber because of the head gasket leaking internal it will do a number on the piston especially on the exhaust side.Was the ring land broken away on the piston ,if not you got lucky.That sucks just after getting the cylinder replated. :(

 

[DEANSFASTWAY]

Actually I think there may be something different about the front studs on the cyl , something about there relationship withthe head gasket holes like the front studs flanges stick up a bit out of the cyl base and the gasket holes are larger in that area , you better take a look. Or maybeIm wrong . Maybe it got hot when you first ran out of gas and the head swelled or something then it leaked a little . You did start out with a new piston new bore . Probably was pretty tight.

 

[DEANSFASTWAY]

One time I had a GP rider come from PORTUGAL and we loaned him a new YZ 125 and he rode the bike for a week or so then we put in a VERTEX trick piston and went to Diamond back NY track and he seized it up tight on the second lap of really muddy practice. You would have thought he would have stayed out of the mud . Then we loaned him an old beater I had for sale and he went out and toremost everybody up.

 

[tracy harman]

the ring land wasnt busted away it was melted away. the front 2 studs are different they are shorter and wider than the rest they are in the correct place.

 

[marcusgunby]

Sounds like detonation to me-i double upo the head gaskets on the 125-can you do this on the 250?or a good product is silkolene pro boost to improve the octane rating.Always use the best fuel you can get.Trouble is ,if the water came out due to dirt on the rad cap then it will have got really hot and detonated anyway.


Read you post again, now if those 2 front studs were not tightened down fully you will have blown the head gasket-maybe the threads were not clean originally?