VN Think I Need A Vent

Jason Annen

H-M Supporter - Gold Member
H-M Supporter Gold Member
Joined
Jun 6, 2015
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283
Been running the 12 pretty hard this weekend. Now I have a puddle of oil on top of the gear box.

IMG_20170102_181606570.jpg

I think I'll install a crankcase vent.

Jason
 
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You think the oil got so hot that vapors escaped out from under the inspection plate?

Daryl
MN
 
It wasn't that hot. I am leaning towards air pressure in the gearbox pushing it out. I am not sure though. No smell either.

Jason
 
Air pressure?
A vent would certainly alleviate that.
But how would that happen? Unless, somehow it's sucking in air from a shaft?
Venturi sort of effect?

Daryl
MN
 
I'm not really sure, but a simple test would be to remove the cover and see what happens. I'm not sure what else would push the oil up that high and past the gasket. I'll be back out there Wednesday evening.

Jason
 
Boy, it's hard to believe the oil would leak up hill if I'm picturing the photo correctly. I'd have to guess you are leaking out the gear box gasket because it's not sealed properly and the splash from below is leaking out. I think your idea of leaving the inspection plate off and seeing what happens is the way to go.

From high school chemistry the perfect gas law equation is PV = nRT, or "Pressure times Volume = amount of gas times a constant times Temperature (Rankine or Kelvin)". In a fixed volume like a gear box, pressure goes up proportionally to temperature. But the temp is on the Rankine scale or 459 + your room temp. If it's 70 deg. F, that's 530 R. If the oil heated up 100 F, that'd put the oil at 630 R or a increase in temp of 18%. That means the pressure inside the gearbox went from 14.7 psi to 17.4 psi. There would be some pressure build up but we still have gravity so I don't see how the oil could travel uphill.

Bruce
 
most enclosed, oil filled, gearboxes i have run across have some means of venting to atmosphere
 
The front axle on my tractor isn't vented, guessing they wanted to keep water and dirt out. On a hot day if you open the filler/dip stick it pops out with pressure. It forces oil out the wheel seals, keeps the front wheels from rusting. Have to add about a litre a year.

Greg
 
Boy, it's hard to believe the oil would leak up hill if I'm picturing the photo correctly. I'd have to guess you are leaking out the gear box gasket because it's not sealed properly and the splash from below is leaking out.


Bruce

I think Bruce is on to something, splash lube leaking past the gasket is my guess too.
 
Hard to say from the picture, but it could also be coming from the selector lever shaft in front of the cover. I would clean it up and keep an eye on it to determine the source. I've chased a lot of engine leaks and it usually takes some detective work to track them down. Often something that looks like it is leaking from the front, ends up being from the rear of the intake or head and following the pan rail and dripping off the front
 
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