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Crank Case Oil Vent Leak

Tom McCutcheon

Well Known Member
I was going through a quart of oil about every 9 - 10 hours. It seemed that it all ended up on the belly of my -4. I finally broke down and bought a Super Seperator from Anti Splat Aero. Once I got the leak at the "T" fixed that I installed in #3 cylinder head oil return everything seems to be working great. I also put on the vacuum valve to one of the exhausts which they claim to increase horse power. I have noticed about an extra 100 to 120 RPM. I have a Whirlwind ground adjustable propeller but I have not changed the pitch. I think I'll just throttle back and have the extra umph when I need it. Hope this is helpful to anyone considering such a move.
Tom
 
..........I also put on the vacuum valve to one of the exhausts which they claim to increase horse power. I have noticed about an extra 100 to 120 RPM. I have a Whirlwind ground adjustable propeller but I have not changed the pitch......
Tom

Tom, can you elaborate? I'm not familiar with the vacuum valve you mention. :confused:
 
Oil Seperator - Vacuum valve

Yes, Aero Splat sells an adapter for their oil seperator. Instead of the vent tube leaving the seperator and just exiting out the bottom of the cowl, you weld this tube onto one of your exhaust pipes at about a 30 degree angle. The angel needs to be so that the exhaust creates a vacuum on the tube. On the tube is a one way valve that only allows a vacuum on the vent line. The result is there is a small negative pressure on your crank case making it easier for the pistons to go in. Less pressure on the pistons going in results in the power stroke being easier to push that piston in.

The end result is that I get about another 100 to 120 RPM's. My guess would be that it might be harder to measure the improvement on a constant speed prop. However, if it's there for a fixed pitch prop it's there for a constant speed prop as well.
Tom
 
thats interesting

I was wondering if anything really bad would happen if the valve should fail closed, get stuck?

bird
 
Oil Vent & Vacuum

Bird,

I'm not sure why they even have a one way valve. It would seem to me that the way we welded the tube onto the exhaust wouldn't allow pressure of the crankcase to happen. But then I haven't tried to think of every possibility either. Maybe a good question for Allan of Aero Splat.
Tom
 
The result is there is a small negative pressure on your crank case making it easier for the pistons to go in. Less pressure on the pistons going in results in the power stroke being easier to push that piston in.

It's a case evacuator. It does reduce crankcase pressure (or more accurately, crankcase air density), in some configurations well below sea-level atmospheric.

The goal is two-fold; reduction of windage losses (a hp gain), and reduced oil droplets in suspension (less oil out the breather).

"Less pressure on the pistons going in" does not in itself result in a HP gain as it is offset for the same reason when the same or other pistons move toward TDC.

You need the one-way valve.

My favorite case evacuator was one I did in the mid 80's on a racebike, based on a reed valve cage entirely hidden inside a catch can. The rule book had nothing to say about case evacuation, so it wasn't cheating ;)
 
Dan

So if the valve failed, say stuck closed, what do you think would the result be? Possibly a momentary increase in crankcase pressure? Just wondering, I like the concept.

bird
 
So if the valve failed, say stuck closed, what do you think would the result be? Possibly a momentary increase in crankcase pressure? Just wondering, I like the concept.

bird

...This particular valve can't stick closed. They are designed so if it did fail it would be wide open and the result would be back to stock HP. These are a very dependable part that is used on virtually every vehicle built from 1970 to 2003 and I have never seen a bad one. We have installed a vacuum system on every high performance vehicle and engine for to last 35 years and every performance shop uses these as well. All NASCAR teams use this, along with a vacuum pump that pulls 18" of vacuum in the crankcase. At the high rpm that they run, it typically results in 75 to 90 HP gain. In the case of our 360 or 540cu in Lycomings at 2500 rpm we typically see about 8 to 12 HP. I have had this system on every airplane I have owned or built over the last 33 years with perfect performance. There are numerous advantages with no down side to this system and I will outline them in a video soon as a picture is worth a thousand words and I type with two fingers. Allan...:D
 
Allan, nothing proprietary about that valve. Give 'em a part number or application so they hit the auto parts store and cut one open.
 
thanks Allan

Ok now I understand, seems like it is similar to a pcv on an auto. I like the idea. When I get to the engine part of my build, I'll be giving you a call. thanks

bird
 
...All NASCAR teams use this, along with a vacuum pump that pulls 18" of vacuum in the crankcase.

On my -6 I used this trick and flew for several years with a wet vacuum pump pulling on the breather with the output going to a seperator. I was limited by the amount of vacuum I could pull due to the fuel pump being vented to the crankcase but there was a significant improvement in decreasing oil consumption. On my Rocket have the same setup, but will be able to pull a full vacuum since I have no mechanical fuel pump.
 
My experience

I was wondering if anything really bad would happen if the valve should fail closed, get stuck?

bird

I have no idea what kind of valve Alan is using but I had almost the same set up on my RV4 with the outlet of the air oil separator going to a PCV check valve from there into a 30 deg angled tube welded into the exhaust. The system worked perfectly for about 200 hrs. I did end up with a stuck closed valve and it partialy blew out my front seal. I suspected the valve from the start as I had oil pushing its way out of other places as well on a normaly tight engine. I removed the valve and confirmed that I couldnt blow through either end of it. I didnt think it could fail closed in fact I could see no reason why it should ever be closed, but it did. I reinstalled the tube without the valve and installed a new front seal and had no more problems.
This is in no way a bash on Alans system but a real experience. As a matter of fact I will soon be ordering one of Alans Separators and will be plumbing it exactly as he does less the valve. It looks like a great product.
Ryan
 
that was

my question all along, I have had pcv valves get stuck in auto's. It is one of the things to check when having problems with rough running engines. I like the idea of the valve and will use it when its time, just gotta put it on the checklist of things to check.

bird
 
Great info on this thread about the crank case vacuum system, however, the thread title does not suggest it... I just stumbled across it. I can't wait for some reports back. I want one, but I asked Larry Vetterman about dumping the breather into the exhaust a long time ago and he said it was a bad idea. Is the differance here the check valve or the separator??
 
Great info on this thread about the crank case vacuum system, however, the thread title does not suggest it... I just stumbled across it. I can't wait for some reports back. I want one, but I asked Larry Vetterman about dumping the breather into the exhaust a long time ago and he said it was a bad idea. Is the difference here the check valve or the separator??

...I had a quite lengthy discussion with Larry Vetterman this morning on this very subject. Larry was concerned due to some past experiences he had and wanted to be sure I passed this information along to our customers. Larry installed many of these back in the mid eighties and he said that he had seen a couple of the tubes try to plug up with carbon where they are welded into the pipe. He said it takes a lot of hours for this to occur and the quality of the separator has a lot to do with this problem. If the separator isn't doing a good job this is accelerated. He and I agree that at every oil change one should simply unscrew the check valve and stick a screw driver in the four inch tube and knock out any carbon build-up. That eliminates any possible problem of this nature. I will detail this maintenance in our instructions along with welding procedure to maintain the integrity of Larry's exhaust system. Any questions on this feel free to give us a call. Thanks, Allan...:D
 
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