Trials Australia Forums

my rl250 has started smoking a fair bit just lately. Still has great compression, starts first kick, seems to run fine. Ive sprayed some inox/wd around spark plug, head bolts, head gasket, base gasket etc etc, but no difference. I'm thinking a crank seal? Any other symptoms or things i can check?

You should be able to detect the loss of gearbox oil if the RH crank seal has a problem. If it is leaking enough to see extra exhaust smoke, the gearbox oil level will go down pretty fast
Gearbox oil smoke is usually whiter than normal 2 stroke smoke (normally pale blue), and smells bad
Another thing you can do is see if you can feel anything happening with the air in the gearbox vent hose
Another thing is to lean the bike over to the right with the motor running in neutral (to submerge the crank seal) and see if the the smoking increases
If gearbox oil is getting into the crankcase it has to be via the primary drive side crank seal leaking or moving out of position, the primary drive gear nut on the crankshaft coming loose, the centre gasket between the cases leaking, or a crack in the crankcase where it is in contact with the gearbox (very rare)
Running lean via an air leak to the engine (base gasket, inlet connection at carby) will not cause extra smoke
Other things that can cause extra smoke are:
sunken float in carby causing motor to run fuel rich
over-oiled air filter element letting oil run out and into engine via the carby
getting the motor hotter than normal causing carbon deposits to burn out

Thanks David, its definitely white smoke and doesn't smell like premix. I think you've confirmed my initial thought. Looks like I'm splitting the cases with the first trials event of the year fast approaching!

I once had a RL250 that shot straight in the air under full throttle and caught a bunch of traction when it came down and caused the crankshaft to twist and start pumping oil from the tranny. A few whacks with a brass hammer brought it back in line plus new seals fixed it. This bike had extra flywheel weight bolted on, don't know if it would have twisted without the weight.