I mistakenly put heavy 4 stroke gearbox oil into my 2015 Sherco 300 trials...I ran it for around 10 minutes until noticing the fan wasnt coming on and realised my mistake with the oil. I have just replaced the water pump seals and axle and refilled the coolant and light gearbox oil. The fan is still not kicking in and its blowing loads of smoke out of the exhaust....also the compression seems much higher....Any ideas what the problem is? Thanks!

Edited June 2, 20224 yr by 290

Yes, gearbox oil in engine smoke and smell. Best you can do, is as soon as possible, completely drain the tank and replace with fresh petrol and correct two stroke oil. However, it may need a period or a few tanks to get rid of all gearbox oil. Also check spark plug for carbon build up. If done promptly and properly, I don´t think your engine has taken any damage.  When I was young, I ran hours with gearbox oil in petrol without noticing any permanent damage.

Thanks Carl, I had no issue with fuel, I added the wrong oil to the gearbox....

I would bet your crankcase seal is bad on the clutch side. The heavier oil just made it obvious.

Or you have a head gasket leak. White smoke or black/blue?

Edited June 2, 20224 yr by lineaway

Gearbox oil should have no contact with engine. Thick gearbox oil may possibly affect gearchange and clutch action (if the same oil). Unless oil leak would not have anything to do with engine.

10 hours ago, lineaway said:

I would bet your crankcase seal is bad on the clutch side. The heavier oil just made it obvious.

Or you have a head gasket leak. White smoke or black/blue?

The smoke is white and plentiful...

White should be a head gasket leak.

Disconnect the fan switch & use a short piece of wire with the right connections to bypass the thermoswitch, if the fan runs as soon as the bike starts then the thermoswitch needs replacing

The smoke is possibly from a leaking head gasket from lack of fan, check the coolant level in your radiator & if it's not above the top of the fins then that's a pretty good indication of a leaking head gasket

Doing the head gasket is simple as long as the head is still flat, remove the nuts holding the head down & replace all the o-rings on the underside of the head

 

 

1 hour ago, tony27 said:

Disconnect the fan switch & use a short piece of wire with the right connections to bypass the thermoswitch, if the fan runs as soon as the bike starts then the thermoswitch needs replacing

The smoke is possibly from a leaking head gasket from lack of fan, check the coolant level in your radiator & if it's not above the top of the fins then that's a pretty good indication of a leaking head gasket

Doing the head gasket is simple as long as the head is still flat, remove the nuts holding the head down & replace all the o-rings on the underside of the head

 

 

Thanks Tony, makes sense, Ive realised the the wrong gearbox oil was not connected to the smokey exhaust and lack of fan!