My 2002 CR125 won't start?

Question

While in 5th the bike locked up for a second then died...I started it back up and about half and hour later it did the same thing and now i cant get it started. I tried new spark plug, completely cleaned the carburator, but dont have much experience taking the top end apart. Any ideas what it is? I'm guessing i blew the top end.

Answer 1

If the piston & rings have never been changed, then the top end is most likely the problem.
Maybe a part of the piston ring broke off and got jammed in a cylinder port.
Could be crankshaft bearings.
Bottem end rod bearing.
A part of the transmission getting stuck and locking the engine momentarily.
Do a commpression test to check the top end.
For a quick check of the top end -
Remove the exhaust pipe and look in the exhaust port with a flashlight and mirror.
Purchase a shop manual for instructions on removing/repairing the top end.
http://www.motocom.com/motorcycles/

Answer 2

Your engine probably "soft-seized." The top-end overheated and locked up. Since your bike is two-stroke you shouldn't have too much trouble rebuilding the top-end. Get a manual and have a good machine shop hone the cylinder or bore it if necessary. They can tell you what size rings and/or piston you should order. Best of luck! Make sure to get a muffin pan to sort hardware, when you disassemble things keep the hardware grouped, i.e.: radiator hardware, chassis/plastics hardware, head hardware, etc. It'll make it easier to assemble. Ziploc bags work as well.

Answer 3

well, if you think you blew your top end and have no exoerience then you may have to take it in and service it but if your're a do-it-yourself kinda guy you probably need to replace the rings which is a simple job, start eith that first if you dont have compression and then go get the top end done which is a kinda complicated job did u check the oil??
do u mean 5th gear?? does it have a 6th if not then u most ikely blew it?