Positive Crankcase Ventilation

[Shepard]

One of the problems with big bore engines is keeping the bottom end pressures in check. When the piston goes down in the block it pushes the trapped air under the piston out of the crankcase vent -- when it goes up it pulls air in. At an idle there isn't much of a problem, but as the rpm increases the vents ability to release the pressure under the piston is compromised most of the time by hose size. If it were a Harley the pressure would be doubled cause both pistons travel off of one crank pin.
What happen if the pressure gets to be too much? Well the first is loss of horse power cause by the engine fighting itself against the bottom pressure. Second is oil leaks and possible blown seals.
There is also blow by from the compression - don't matter how perfect the rings are there is a small mount of gases the make it to the bottom end.
The original valve cover has a simple check valve in it and it helps. If you change valve cover like to the Aussie Speed valve cover there is no control valve in the cover. I put a one way check valve in my valve cover to stop any air from being pulled in. The more of a vacuum you can create in the bottom end -- the less chance of a gasket starting to leak. It will also help increase your horse power.

[jjastram]

Thank you, I did exactly what you said would happen. I tapped threads in the Aussie cover, screwed in a barb fitting, hooked up the hose to the air cleaner, and away I went. I ordered a check valve.

[raydhd]

After seeing your thread and reading some hot rod columns I also ordered one. Shepard leads the way again.

[Shepard]

The other day I drove my cart to the farm. On the way home I would smell oil burning from time to time - nothing bad. When I got home and looked the dipstick had been popped out of its seat and was spitting oil on the exhaust. At the same time my breather hose had spit out on the fuel tank. I don't think the original valve cover vent is enough to do the job right. I'm going to stretch the swing arm of my cart and will be changing my vent system.

[raydhd]

No matter what I did the original valve cover would leak. I have had zero issues since going to the Aussie speed unit. I just pulled it off today to do a valve adjustment check. The exhaust was very slightly loose. The intake was still dead on. I checked the inside of the cover ,my fitting ,and my hose off the fitting in the cover. All super clear. And this is with me high filling my crankcase to the max.

[Shepard]

Check out your original cover. With the vent hose pulled out there's a metal tang sticking out to the center of the vent hole. Looking in the vent hole -- at the same time push up on the plastic valve inside of the cover -- if you push your vent hose in to deep into the valve cover, the hose will hold closed the valve not letting the engine breathe. Can lead to leaking or blow gaskets -- I think that is why my dipstick popped out. The Aussie Speed cover breathes much better -- I tapped the valve cover 3/8"NPT used a chromed 90 degree fitting and a 3/8" NPT PCV valve and a stainless steel vent filter.

[raydhd]

I tapped in 1/4 "NPT air fitting with 3/8" hose over that. Coming is a 3/8" barbed aluminium gas/ diesel check valve.

[sho305]

I tapped my stock cover and ran a hose to the airbox, no oil out of there yet. But still has the stock cam in it too. I had oil leaks before but it was because I didn't loctite the bolts in, they still had the original stuff on the bolts and thought it would work, engine was not run yet when I took the governor out.

[raydhd]

Originally Posted by raydhd

After seeing your thread and reading some hot rod columns I also ordered one. Shepard leads the way again.

The pair of 3/8 aluminium check valves came in today. Really nice. Too bad it will be buried down in the engine compartment.

[HBR]

Shepard - how did you tap your Auusie cover? I just got mine today and that baffle sits so close that I cant see running the tap in very far before the tap hits the baffle.