I picked up a 1986 CR 250 awhile back in generally good condition but not running. The PO said the radiator plugged up and it got hot and cooked the piston. The piston was toast; a chunk cracked off the side of it, above the ring, on the exhaust port side. The bike went on the back burner for quite some time and recently I have begun to work on it. I sent the top end off to be redone. It had been previously sleeved ( ) so I had a fresh sleeve installed and bored to stock. They also cleaned the powervalves and everything else I guess. The top right bolt on the right side power valve cover won't torque down and spins freely, not sure if it was like that before the work was done, but I will need to fix that. I purchased and am in the process of installing a wiseco piston and gasket kit for the bike right now. There was no lateral crank play in the bottom end and no vertical play in the rod against the crank. Ring end gap checked out fine with a .008 gauge. I put the rings in the cylinder, pressed them down with the piston to get them even and used the feeler gauge pushed from the center of the cylinder to the wall of the cylinder in the gap. It fit and didn't seem to be a problem. The max spec (I think it is .012? I don't have my manual with me right this second) did not fit but I don't see that as a problem obviously. So right now I have the gaskets installed into the top end, bolts are torqued with one exception, and I should be installing the piston over the weekend when I have the time. The next step after that concerns me. I don't know for sure if the radiators are clogged, I don't know how to test them. I don't know what the PO knew or if it was even the truth. The water pump cover didn't look seriously corroded, wasn't missing any chunks, but everything in the coolant system (which has been dry for awhile) does have a white powdery film. I was leaning towards buying some ebay radiators + silicon hoses for ~$135 shipped so I have a part I know is "good" and will work. I do not know if I can clean the radiators myself and I really don't want to have them cleaned if the money that will cost would be in the same ball park as new radiators. I also don't know what kind of coolant to run in the future to prevent corrosion and breaking the bike. This is my first time doing a top end and I am comfortable with being able to do a lot of work myself. This is the farthest I have ever been into an engine but I have experience working on things from my motorcycles ATV and snowmobiles. I also have an xr100 that I have done some small work on, but that was just involving flywheel/stator/electrics stuff. A lot of people told me to quit this, and probably will continue to tell me to quit, but the bike ran before and I see no reason that it can't run again. I just want to make sure I do it right the first time because I don't want to sink much more money into it.