Bike siezed up.rocking it frees up and starts but locks up
The piston seize destroys the piston, rings and cylinder wall. Bad enough, and repeated seizing, can get metal bits into the crank rod bearing and crank end bearings and seals. This is serious stuff. Sorry to be the bearer of bad news.
Seizing is caused by friction. Not enough lubrication means friction that creates heat. The heat builds and the piston and rings "weld" to the cylinder. A faulty cooling system can also cause heat. Any oil will break down and loose it's lubrication ability when the heat gets too high. A water pump malfunction or plugged coolant lines, leaking coolant hoses, plugged radiator and bad gaskets can create heat.
Other sources are > timing is off, air leak causing the fuel to be too lean, incorrect spark plug heat range, carbon buildup on piston and head causing detonation, motor oil used in gas instead of 2 stroke engine oil and over revs on the engine. I have probably left a few things out but these are the usual causes. Be aware that combinations of small problems can add up to a seize.
The engine needs to be rebuilt. Normally I would just rebuild the top end but since you have had multiple seizes the bottom end is probably contaminated. New crank bearings and seals should be installed. If the cylinder can't be bored then you will need a new cylinder. New piston and rings are also required. Bear in mind, you must find the cause or causes of the heat and fix those problems also. If you don't, the new piston will quickly seize up.
Top rating for this answer! Thanks Kev...
May 06, 2009 |
2003 Yamaha YZ 250 F