Two stroke trouble

[Airinout georgia]

I need some input from you guys. Unfortunetly, I have a '99 cr 125 as well as my trx and everytime I get 2 or 3 hours on it the damn thing blows the head gasket in the same spot everytime. The head and cylinder decks are true as can be, but the gasket always looks like the cumbustion blows threw that one area and melts the metal gasket. I'm going on the fifth one in two years and have only got a total of ten hours of riding. I love the bike but I can't rely on it to be dependable so all it does is collect dust. Anyone got any promising advice?

[69quadracer]

You might try some spray on copper cote on the head gasket, spray on both sides let set and recote and in stall and be sure you torque to spec.

[Here 2 help]

The 99 CR is pretty simple. Blowing head gaskets indicates one of a few things. First, make sure the shouldered head studs are seated all the way into the recesses on top of the cylinder. If memory serves me correctly, the two studs on the front do not seat as deeply as the rest and act as alignment for the head gasket. Providing the two front studs are not causing the problem, check to see if the cylinder has been "milled" for higher compression. If the cylinder surface was "planed" but the stud seats were not relieved, then the stud flanges might prevent the head from tightening against the head gasket. (Same would be true if studs simply were not fully seated) Now check the head. Over-tightening can distort the head. This can be temporary (each time the head is removed and installed if overtightened each time) or permanent. Have the head and cylinder trued by taking them into a machine shop and have the surfaces checked by lathe or vertical mill (I prefer lathe). Either way, try not to have more than .005 material removed from either. If the cylinder needs to be trued, the stud recesses will need to be relieved the same amount as was removed from the top of the cylinder. Finally, be sure not to over torque the head nuts. Tighten in 2 to 3 steps, in a criss-cross pattern, to a final torque of about 20 ft lb. (Note: head nut torque value is not critical. It is more important to be even than to be accurate. Torque of 18 ft lb is probably sufficient and up to 26 might be OK, but over 26 you might start to do damage) Also, have your torque wrench checked. You might be over torquing without knowing it. Finally - NO SEALANTS! - clean and dry is the rule. Remove all the old gasket by rubbing with steel wool or glass bead blasting, then wipe the gasket surfaces with fresh solvent (lacquer thinner, denatured alchohol, acetone etc.). Do not use gasoline - it leaves an oily residue behind when it dries. My guess is you will find the problem in the head studs and the gasket always blows on the front side of the cylinder.

[wolfsnout]

You may have a clogged gas tank vent. That will cause it to burn lean and melt the gasket. Seen them do worse then that.