Yamaha DT175C blows white smoke

[Vince H]

hi my dt175 is blowing a heap of white smoke out the exhaust can anyone tell me reasons why??

[sleepy]

How long has it been doing it for? When is it doing it? Is it getting worse?
Could be sucking in gearbox oil.

[pokey]

How did you get it to do that neat trick?
Stinks a bit aswell?
  Gearbox lube for sure. Could be centre gasket or main seals but either way its not going to be a fun job

[David Lahey]

not much info on the history of the motor to go on but here is one about those motors that may not be common knowledge:

there is meant to be an o ring at the spacer behind the primary gear on the crank. If you motor has just been worked on, and that o ring wasn't replaced, that might be where the gearbox oil is getting in. It's an odd size o ring and some people leave it out or use the old one

[yamaico]

Couple of tests to determine whether it's the seal:
Has the gearbox oil level gone down?
When the bike is running lay it over to the left hand side to let the gearbox oil away from the seal. If the seal is bad the smoking will stop and it should start to suck air and run a little lean.
As David says, that o ring is critical, but even if it's the seal it's an easy repair.

[TT5 Matt]

buy the old girl a seal kit and some outer cover gaskets as if there factory fitted seals still in it they would be hard and starting to develope cracks

[bazza]

As Yamaico said