VW Crankcase vent

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Pops

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I was having a small problem with a oil leak around the prop hub seal. The area around the seal would have an oil film and after flying a few hours a light oil mist would be on the windshield. I built a reed valve like the 1/2 VW boys use to run a neg pressure in the cut case VW. Made from steel feeler gauge material maybe .005. Mounted it in the alum box bolted to the gen stand location with a thermos bottle sealed plug to add oil. The oil goes under the reel valve. With running a vacuum in the crankcase, you have no oil leaks and the prop hub area stays dry. I did like the VW company and ran the 3/8" breather line to the intake of the carb. I have a fiberglass tube that runs from the carb intake to the airfilter box. Drilled a hole about 2" in front of the carb intake and cut a bevel on the end facing the carb and epoxyed to the FG tube. Now with running a vacuum in the crankcase, I have no oil leaks. The area around the prop oil seal stays dry. You also will get a small increase in power by the crank running in a vacuum.

Dan
 

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Hot Wings

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I've always thought this should be SOP for VW conversions. Did you make the reed box or is it an off the shelf item that I haven't seen before?

Also I see safety wire holding up the lower cylinder air deflecting tin wrapped around the head stud?
 

don january

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Very well done Dan, Like Hot wing's said It should be SOP. I wonder what Shark Tank would offer for the design:)
 

Pops

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I've always thought this should be SOP for VW conversions. Did you make the reed box or is it an off the shelf item that I haven't seen before?

Also I see safety wire holding up the lower cylinder air deflecting tin wrapped around the head stud?
The safety wire is helping to hold the lower cylinder air baffling that Great Plains sales. They are a stock unit from VW stationary gpu's

Made the reed valve myself from a piece of aluminum and a piece of feeler gauge material of about .005 thickness.

I guess you could use an auto PCV valve if you wanted.

Dan
 

cheapracer

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Get down to a motorcycle wreckers and get one of millions of reed valves and an intake manifold made for 2 stroke motorcycles since 1972, 80cc or 125cc will be fine, probably charge you 5 bucks and you just saved yourself many hours.

To take full advantage of lowering the pressure in the crankcase, you need to run a windage system as well. The extra HP comes not from running the crankshaft in the lower pressure, the crankshaft itself causes low pressure areas travelling behind the crank webs and big ends as they spin and these areas gather oil referred to as an "oil rope". I don't know about the VW but a typical V8 can hold up to 2 liters of oil rope around the crank.

By lowering the crankcase pressure it makes it easier to separate the oil rope from the crank by getting the pressures closer together but you need a scraper to remove it and a separating shield/tray to help prevent it being picked up again - in other words, you need a complete windage system, not just a one way valve (PCV).

However even a basic PCV, as with Pops setup, will indeed stop oil leaks and increase engine life. Oil rings do not "scrape the oil", in fact the 2nd compression ring does more scraping, the oil ring gathers and positions bore wall oil to be extracted through the holes or slots in the piston via pressure differential. The PCV also increases this differential and makes the oil ring's job easier. This also lowers the risk of detonation from oil contamination in the charge (blow by).

Ultimate PCV/windage systems will also include an exhaust PCV system, I would think this is mandatory for a constant rpm aircraft engine as there's as much to be gained as an intake manifold system, it's not rocket science and many kits are available, Google "exhaust evacuation systems". Some of you will have to get your head around the fact that the exhaust offers a vacuum (sic), not just pressure.
 

Pops

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Get down to a motorcycle wreckers and get one of millions of reed valves and an intake manifold made for 2 stroke motorcycles since 1972, 80cc or 125cc will be fine, probably charge you 5 bucks and you just saved yourself many hours.

To take full advantage of lowering the pressure in the crankcase, you need to run a windage system as well. The extra HP comes not from running the crankshaft in the lower pressure, the crankshaft itself causes low pressure areas travelling behind the crank webs and big ends as they spin and these areas gather oil referred to as an "oil rope". I don't know about the VW but a typical V8 can hold up to 2 liters of oil rope around the crank.

By lowering the crankcase pressure it makes it easier to separate the oil rope from the crank by getting the pressures closer together but you need a scraper to remove it and a separating shield/tray to help prevent it being picked up again - in other words, you need a complete windage system, not just a one way valve (PCV).

However even a basic PCV, as with Pops setup, will indeed stop oil leaks and increase engine life. Oil rings do not "scrape the oil", in fact the 2nd compression ring does more scraping, the oil ring gathers and positions bore wall oil to be extracted through the holes or slots in the piston via pressure differential. The PCV also increases this differential and makes the oil ring's job easier. This also lowers the risk of detonation from oil contamination in the charge (blow by).

Ultimate PCV/windage systems will also include an exhaust PCV system, I would think this is mandatory for a constant rpm aircraft engine as there's as much to be gained as an intake manifold system, it's not rocket science and many kits are available, Google "exhaust evacuation systems". Some of you will have to get your head around the fact that the exhaust offers a vacuum (sic), not just pressure.

You are correct .
I used to build hot street VW's set up for road racing. Without a windage tray and a extended sump, pulling enough G's in a turn the oil in the sump would be on the side of the sump un-porting the oil pickup tube. So making a small sump and extended the pickup tube down in the sump to stop the problem.
I have a small sump on my 1835 cc VW engine and extended pickup tube, but no windage tray.
In this picture you can see the small sump and the oil drain plug. In an auto, the sump would be bigger. Sometimes I like to play a little.

Dan

Added -- Building a new flywheel end prop drive 2180 engine. It will have a windage tray and a much larger extended sump instead of a dry sump system. The carb will be mounted on the bottom of the sump with the intake inside the sump taking the place of my hot oil box. Just like a Lyc engine.
 

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Hot Wings

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The safety wire is helping to hold the lower cylinder air baffling that Great Plains sales.

Dan
That's what I thought. Just trying to point out another little detail that is too often missed on VW conversions. I've seen the result of lower cylinder tin coming loose and causing wear through on the push rod tubes, and even cutting head studs enough that they broke.
 

Pops

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That's what I thought. Just trying to point out another little detail that is too often missed on VW conversions. I've seen the result of lower cylinder tin coming loose and causing wear through on the push rod tubes, and even cutting head studs enough that they broke.
Did you notice of the lack of a oil dipstick? The location of the stock dipstick would be behind the nose bowl and very hard to use, so I made a new dipstick location at the rear of the case and calibrated for tail up and tail down oil levels.
 
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