For those who have done the crankcase vent mods.

After you have done the crankcase vent mod, have any of you then had any problems with oil leaks or going through more oil? I have done the mod to my 84 and got a very slow leak afterwords. I also put a vacuum cap over the orifice that the PCV valve went to on the air cleaner, which then mad it sound as if a tribble was stuck in my air box. I'm guessing the air was blowing over the orifice on the inside of the air box making it whistle a bit. Kind of like blowing across the top of an empty rifle shell. I'm gonna undo the little mod this spring and see if things change.

PCV = Positive Crank Ventilation. When installed it creates a slight negative pressure, (vacuum), in the crankcase. So if there happens to be a small leak somewhere or a worn seal, the negative pressure won't let the oil leak out. If the PCV valve is eliminated, the result may be a positive pressure inside the crankcase as the engine warms up, and due to blow by. Which then might cause a seal or gasket to weep a bit of oil that might not have done so before.

I tried this on my 78 F100 once just to test my theory. The results confirmed my suspicions.

Any thoughts?

Attached is Tech Notice from Yamaha on fixing oil leak in MKI's

Gary

Well that explains why I saw that setup on the 83 I picked up for parts.

But I was referring to when people eliminate those hoses all together and install a small breather/filter and let the case vent to atmospheric pressure. I was having a small problem with the oil inside the air box, so when I redo things in the spring I'll do it like it says to in that PDF. I didn't however have a problem with leaks elsewhere till I did the venting to atmospheric pressure mod and capped off the orifices on the air box. Either it was a coincidence, or the leak was due to the lack of a negative pressure inside the case.

I added the little filter on the crankcase vent this past summer and just plugged the drain and vent lines on the bottom of the airbox. I don't have any excess oil on top of the engine from oil mist through the new filter and my airbox stays nice and clean. Now it is even easier to remove and install the airbox in the future. As long as I don't develop alot of blow-by or overfill the oil level then I don't expect to see any external oil leaks from this modification.