2000 cr250 compression issue

[Mitchell Stuhl]

If anyone has a suggestion please help?
I had the cr250 rebuilt bottom end and top end and took it to the dunes in california. I ran it hard and it ran great for three days then on the last day it blew. It was hot and I was probably running it too hard. Here is what is going on. After I heard it blow to get back to camp I ran down a large hill and it started again and I idled it back part way to camp. I was amazed it even started again because when kicking it over it had minimal compression. I drained the oil, and no water in it. I stripped off the carb, reed box, and exauhaust. I inspected the piston from the exhaust (front) and from behind (reed box). I did not see any piston damage. I did notice one reed box screw not real tight? I am wondering if I have a blown head gasket, if anyone can advise before I go any further please let me know, Thanks!

 

[sharky243]

Are you loosing coolant through the exhaust ? Any signs of dirt ingestion ? What does the plug look like ? Did you break it in properly ?

 

[jason33]

probly burnt the rings,and cyl , needs honed, to break the burnt crap,and a new dset of rings,maybe if your lucky

 

[Mitchell Stuhl]

2000 cr 250 piston/cylinder damage

I pulled off the head and the piston is fryed on top. The cylinder is chared too, only near the top. I guess I need a new top end. How would I know if the bottom is good?

 

[whenfoxforks-ruled]

You seemingly may have blown a head gasket, you should be able to see the leak area. Never read it seized? So the anti freeze was boiling while you drove it more? Try some wd40 and lightly match the crosshatch angle with a green scotch brite pad, LIGHTLY! Clean the top of the piston the same way, wipe the rest of the piston down and make sure the ring grooves are clean. Measure the skirt clearance with a feeler gauge. If it is past the service limit, you need to get the bore measured. Check the ring gap also, especially about 1/4 inch from the top. Clean the head dome, and resurface the head. Check the top of the cylinder for areas that look different, possible leak areas. Check your cylinder studs for being seated all the way down, any iffy threads, replace them and the nuts. At that point it would pay to resurface the top of the cylinder. And of course, douche the bottom end. See what breaks down the anti freeze film, hot dish soap water usually cleans all. Spray liberally with wd40.