Gearcase oil leak?

[shizznats]

Before starting our LTD engine after the top end rebuild, I decide it would be a good idea to check the gearcase oil level. I wasn't able to see anything through the sight glass, so I decided to just drain the oil and add new oil... it's only 80cc's...

To my surprise, however, only about 25cc came out (and that was with the back of the sled lifted up some). I had just filled the gearcase with oil about 5 months ago and put in 80cc's. Is it likely that I have a leak... or does the rear of the snowmobile have to be lifted a LOT to get all the oil out? Thanks...

[mswyka]

Mike, you never really get out all that you put in, but most of it should come back.

[gixxer6]

Bad crank seal?  If your crank seal is bad on that side it will suck the lube into the engine...

[shizznats]

We changed both the PTO and MAG crank seals and the engine passed a crankcase pressure test (held 7psi for 10+ minutes) so I am guessing that should mean the crank seals are holding? I will just fill the gearcase again, wipe the crankcase clean and see if I can spot where it's coming from. What angle should the engine be on when checking the gearcase oil sight glass to make sure it's filled properly? The engine is currently out of the cradle.

[jimvw57]

Thus my problem with the crankcase pressure test.... If the crankcase was under pressure, that would be fine. but it isn't. It alternates between vacuum and pressure. It may hold pressure but NOT hold a vacuum. That would allow the motor to draw in air past a seal, leaning out the mixture and melting a piston. There is no way to test for this unless you seal the intake and exhaust, and draw the whole inside of the motor with a vacuum.

All you can do is assume it is an internal seal unless you see a leak on the outside. It has to be going somewhere.

[shizznats]

That's a great point. Crankcase pressure only tells half the story really. I will check to see if I notice any leakage on the outside of the motor and go from there. Thank you all.

[gixxer6]

Did you change the seal behind the oil pump gear? 

If all your seals are new, that's probably not your problem.  I would continue with your plan of filling it and checking. 

[jimvw57]

I fought with a motor for a year and it ended up being a seal that was put in dry by the previous owner and the center was completely ripped out. I always pack the seals with grease. If you didn't put the seals in yourself, you really don't know what the last guy did...

[bryan_damone]

Unlikey for the seal behind the gear to be dry as it is bathed in oil. 


I assume you replaced the other other seal for the gear case on the crank as it comes with the gasket kit?  Just top it up and monitor. Even if you have a leak into the gear case, its oil not air...or not much air anyway.