Posted Wednesday, January 3, 2007 @ 01:08 AM  

Do you lose a lot of oil from your breather when flying aerobatics? I do, but I hope I've minimised it.

Firstly, it is easy to over-fill the sump, so excess oil can then blow out of the breather. A VW holds just 2.25 litres of oil, but what appears on the dipstick depends on whether you are using a proper Rectimo dip-stick (calibrated for the tail-down attitude) or a standard VW one (calibrated for a level car). Also, because this is at the engine's forward left corner, the reading is affected by which out-rigger is on the ground, and even by tyre pressure and bungee stretch, or tailwheel diameter, or its rubber's condition.

I found the answer was to drain all the oil from the engine overnight (with the wings level and tail raised, so it all comes out) then re-fill with exactly two-and-a-quarter litres and allow time for the oil to find its way down into the sump. With the aeroplane on level ground, the tyre at normal pressure and the left outrigger down, this dipstick indication becomes your datum. Always fill to this and you know you have the right amount of oil in your sump.

If you can, it is important to fit the multi-louvered, pressed-steel Volkswagen breather baffle between the crankcase upper face and the breather cover plate (and be sure to get it the right way around). This deflects and condenses much of the oil mist, so it trickles back into your sump, rather than going down the breather pipe.

If your engine's capacity has been increased (from 1,200cc to 1,400 or 1,600cc) you will need to increase the breather's bore, otherwise those bigger pistons will pressurise your crankcase and oil will blow out forwards through the crankshaft oil seal behind the propeller (not really a seal, just a revolving spiral machined in the crankshaft).

If you are flying a lot of aerobatics with negative G, your oil will slop to the top of the engine when you are inverted, and crankcase pressure will blow it straight overboard out of the breather. You can reduce this by extending the breather tube down into the crankcase by a couple of inches, but then it gets close to the crankshaft/camshaft drive gears and gets a lot of oil sprayed up into it. All your oil will go by the time you reach 1,000 feet – ask me how I know this.

You can minimise this by crimping the lower end of this tube closed and drilling a few holes in its side furthest from the gears. Be sure the total area of those holes is greater than the cross section of your breather pipe (or, see above). Adding a deflector plate made from half a larger diameter tube helps further. Here's my stack-pipe without its protective shield:

My final solution was to make a rectangular oil catch tank for the breather. This is fitted between the engine and the firewall on the left. The breather goes into it at the top, with the tube extending down inside to slightly past the half-way mark. The outlet comes from the bottom, but again its tube extends upwards in the tank to just past the other one, and it is closed at the top, with its inlet at the side. The breather tube from this goes back under the aeroplane’s belly to below and just aft of the trailing-edge. Very little mist now comes out of here.

The tank holds around a litre of oil, which is enough for twenty minutes of full-on positive and negative G aerobatics. I drain it after each flight through a Curtis (fuel drain) valve in the bottom. The tank is made out of thin-walled, rectangular-section, steel Australian gutter down-pipe, which fits perfectly. The ends were cut, shaped, bent over, pop riveted and sealed with Proseal (homebuilt fuel tank sealant). Ten feet of half-inch aluminium tubing, some P-clips and a few AN bulkhead fittings were the only other aviation materials. Total weight: a few ounces.

All this is important stuff, because oil (especially hot oil) can quickly ruin a wooden structure. If you let it spray out of the original firewall breather, it runs back all over your main spar. This is most definitely NOT a good thing.

There are photos of this mod (and some of my other mods) posted on the web site.

I would love to hear anybody else's thoughts or solutions on this subject, because it is one I have struggled with for three years and, while I have a solution, there are probably more elegant ones. Like, perhaps a new breather could be drilled with a tube right into the centre of the engine, so it would always be above the oil level, whatever the aeroplane's attitude.

Fourniers forever.

Bob G

Posted Tuesday, January 5, 2010 @ 11:43 AM  

My Grob109 Limbach (VW) has the breather going to a air/oil seperator mounted high on the firewall with the oil
drain feeding back into one of the rocker covers.

It still leaks a bit though.

Posted Friday, January 8, 2010 @ 11:53 PM  

Here is my current installation, successfully tested yesterday in Australia.

I have not yet precisely compared the amount of oil lost through these, against that lost with the earlier system, but expect to do so within the next week.
I can tell you that although of course it does lose oil during rolling manoeuvres, WGN loses no oil at all with these breathers when I confine myself to outside loops. I did around ten with no oil loss at all.

More to come.

Posted Saturday, January 9, 2010 @ 08:52 PM  

I so wish I had known about those a year ago!

Posted Thursday, April 1, 2010 @ 10:33 AM  

http://www.vwparts.net/mm5/merchant.mvc?Screen=PROD&Product_Code=BP4539&Store_Code=VWP&search=valve+cover+vent&offset=0&filter_cat=&PowerSearch_Begin_Only=&sort=&range_low=&range_high=

I dont think my RF4D even has valve cover venting.

It got me to thinking that perhaps you dont need a vent at all, since any presure leaking through the valve stems would go back
into the case via the pushrod tubes and the single case breather would be the place where excess pressure exits the engine.

What is the purpose of the valve cover vents? anyone?

[Edit by jb92563 on Thursday, April 1, 2010 @ 10:41 AM]

Posted Thursday, April 1, 2010 @ 10:08 PM  

I tried Vee Dub but
a) they only use paypal and
b) they still wanted $36 to ship a $6 item, so I'll forget it.

Posted Friday, April 2, 2010 @ 10:14 PM  

Yes please, if you are buying a pair for yourself, would you please buy two pairs for me, pop them into a small padded bag and mail them.

I'll send you a check in U.S dollars for the required amount.

That is very kind of you.