kdx has blown

[bionnick]

so it took the kdx out for a blast a few days ago and i heard a noise that sounded like i was dragging a bag along the road but was coming from the engine so i shut it off as i was outside my house so i dumped out the gear oil and put in new and started it up and it sounded fine after running for about ten minutes so i just turned it off and went in, anyway i took it out again yesterday and got 10 minutes down the road and heard the noise again and pretty much instantly the engine just died, i pulled in the clutch and let it back out at about 5 mph and the rear wheel locked for a moment but then was free again, i got my mate to pick me up in his van and got the bike home and took the head off and the piston and barrel are both heavily scorred but the rings are fine and intact so something must have come up out from the bottom end, i will split the crank at some point this week and let you know what i find, i feel well gutted :(

 

[bionnick]

on further inspection the bottom end seems fine its just the piston and barrel, theres a bit of cylinder wall come off and done all the damage, i will get the cylinder re-plated when ive got the funds.

 

[dirt bike dave]

You are lucky the problems seem to be top end only.

OTOH, if you intend to keep the bike, this might not be a bad time bite the bullet, split the cases and put in new crankshaft bearings, and take a very very close look at your crankshaft, including the big end bearing.

Hard to justify spending big bucks splitting cases and doing preventative maintenance on an old bike, but if you do have a catastrophic failure in the lower end, it can destroy the cases, the cylinder, the KIPS valves, etc...

Finally, if you are using the bike on the road or dirt roads, make sure you pull in the clutch when slowing down and avoid engine braking from high speed after a long hard pull through the gears. I learned the hard way a red-hot, pre-mix two stroke dirt bike does not like it when you shut off the throttle and coast from high speed. Heat + rpm - cooling fuel and lube = failure of the weakest link.

 

[bionnick]

thanks i will remember this for the future.