Tuesday, February 27, 2007

VW = Degrees for Free

See equals pie dee.

So... whats the dee of your pullee? (Careful here. VW used at least three.)

If you know the dee you can figger out the see...

...an once you know the see you solve for degree.

How? Last time I checked every see has got three hundred and sixty degrees so
see over three-sixty gives you one. Degree, that is. How many you need?
Seven point five? Twenty-eight?

Then all you gotta do is measure them out on your pullee,
mark 'em good,
make'em shine,
keeps the engine in tune and the ignition on time.

If you got a #2 yaller pencil... or even a #3... it's a breeze to track down a
missing degree.

There ya go. Degrees for free.

-Bob Hoover

PS -- Or pony up the bukz and buy a degree wheel. Full size, please. But
before installing it, give it a bath. Detergent & water & a good rinse after.
Then put a paper down in a glass dish, pour in some vinegar or other mild acid
and put your clean degree wheel numbers-down into the dish.

The numbers are only painted on (and not always accurately -- best to check).
The acid will etch the aluminum. Not much. But enough. Thereafter, when the
painted numbers on your crappy, non-engraved, sellum-to-the-kiddies degree
wheel vanish, as they always do, the acid etching will remain... along with the
image of the numbers. -- rsh

PPS -- What's a GOOD degree wheel cost? 'bout a hunnert bucks, all nicely
engraved (the markings will never wear off), anodized (the pulley groove won't
wear out) and balanced.

AV - Manually starting the VW Engine

> > Please explain to me the adjustments/mods to be made to my 2.0l Type 4
> stock distributor to facilitate easy hand propping. The engine will
> drive from the flywheel end.

There are four key factors involved here. (Although I may add more later :-)

1. Engine Assembly
2. Ignition Timing
3. Propeller Orientation
4. Type of Ignition System


1. Engine Assembly

There are two areas of critical concern, the first is cam selection, the second is accurate assembly of the engine, especially with regard to your valve train geometry.

With regard to the cam, most VW engine converted for flight are hot-rod engines -- something you'd expect to find in a dune-buggy rather than an airplane. And as a dune-buggy engine, they are fitted with dune-buggy cams, meaning the torque band has been shifted toward the upper end of the rpm range. This is accomplished by grinding a lot of overlap into the cam and extending the duration, two features never found in a direct-drive aircraft engine. What you want is the stock cam, which happens to have a torque band suitable for slinging a propeller of useful diameter. (There are a few other cams that are suitable. They were used in VW's industrial engines or in VW's converted to serve as orchard blowers.)

With regard to engine assmebly, there's no way I can cover the subject via email. I'm working on a manual that does the job fairly well but it's already over 200 pages in length and I've only just gotten to the heads :-) But as a general rule, you need to ensure that your cam is correctly indexed to the crankshaft. Simply lining up the dots is only an assembly-line approximation, usually accurate to withing +/- 2 degrees or so. You not only want it dead-on, for a low rpm, high-torque engine you generally want to retard the stock setting by 4 degrees. This task is typically referred to as 'dialing in the cam' and requires the ability to rotate the camshaft very slightly relative to the cam gear when the cam gear is locked in place and the engine is precisely at TDC. (How do you manage that? You reach in through the opening provided for the oil pump.)

I covered this procedure in some detail for the Type I engine in an illustrated article that appeared in VW Trends magazine a couple of years ago but the basic procedure will be found in any tome covering professionally built high-output engines.

Once the lower-end is dialed in you focus on accurate valve-train geometry, which is a fancy way to say you ensure minimum lost motion in transferring the movement of the cam to the depression of the valve. This matter is worthy of your attention because it's not uncommon to see loses as great as 25% in this area. (That is, an anticipated 10mm of movement at the valve reduced to as little as 7.5mm due to improper assembly of the valve train components.) The point most fail to appreciate here is that faulty valve train geometry effectively alters the engine's mechanical timing. It isn't uncommon to see a casually assembled stock engine give away as much as 15% of its normal output. (Indeed, it is more the rule than the exception.)

The key point here is that an improperly assembled engine can effect your valve timing, and improper valve timing can make an engine very difficult to hand-prop.


2. Ignition Timing

Don't waste your time here unless you've already confirmed that the engine is properly assembled, because for every degree you're off relative to the crankshaft/camshaft combination, you'll be off by 2 degrees in your ignition timing.

But assuming a properly assembled engine, to ensure easy starting you want to set your static timing somewhere between three and five degrees BEFORE top-dead-center. The closer to TDC, the easier the thing will start... but the farther the timing will need to advance when you open the throttle.

This assumes you are using an ignition system which allows the firing point to advance as the rpm increases (ie, a centrifugal- advance mechanism). You'll not find this in a magneto and only half of it in a stock, late-model Bosch distributor (ie, the 'composite type,' having both vacuum- and centrifugal-advance). The Bosch -009 distributor will serve but you should know that it was never installed on any VW vehicle. It is in fact a generic after-market replacement for the dozen or so centrifugal distributors used on the early Transporter, and for at least that number that were found on VW industrial engines. But it is beloved of dune-buggy types because it is inexpensive and can be adjusted to give as much as 30 degrees of advance. (Typical is 17 to 19 degrees.)

You will want at least 28 degrees total ignition advance, assuming you want to spin your prop at least 2700 rpm. To increase the advance range you simply fiddle with the stops on the advance plate and bob-weights -- a good mechanic can show you how. But proceed with caution. If you file away a tad too much metal you'll find it hard to replace :-) (To increase the advance rate you reduce the mass of the bob-weights and use springs of lighter tension. But that's only needed on dune-buggies, dragsters and the like.)

I hope you can see the quandry here: To make the engine easy to start the static firing point must be near (or even slightly AFTER) top-dead-center. But for the engine to run fast enough to be useful, the firing point must be advanced to about 28 crankshaft degrees BEFORE top-dead-center. If your distributor can only provide twenty degrees of advance (fairly common for a -009 straight out of the box) then your static firing point will have to be at 8 degrees BTDC, which will make the engine slightly hard to hand-prop. Move the static firing point nearer TDC and you automatically limit your peak rpm. (Need I mention proper engine assembly again? I hope not. But just in case... understanding that the relationship between ignition timing and rpm should offer a hint as to why many sloppily assembled engines never live up to their potential.)

Luckily for me I won't have to figure it out since you are the Mechanic-in-Charge :-)


3. Propeller Orientation

You've probably never owned a Model-T Ford but if you had, you would know that there was a certain feel -- a kind of 'springiness' -- in the crank as the piston approached TDC. You would feel for that (with the ignition off) as you charged the cylinders. Then with the ignition ON (and SPARK set to fully retarded), you'd flip the crank past the springy point and the engine would clatter into life. (The Model T's cam didn't have any overlap at all, limiting its maximum rpm to about 1800... and making it superbly easy to start.)

The T4 engine isn't a Model-T but when it comes to manually starting, your prop is still a crank.

With the prop mounted on the clutch end of the crankshaft it's going to rotate clockwise relative to the pilot (Volksplane assumed). That means you want TDC to occur at about 9 o'clock when you're standing in front of the plane facing the prop. The firing point is going to be a few degrees up from the 9 o'clock position, allowing you a 'swing' of nearly 90 degrees. That is, with the cylinders charged you'll bring your 'signature' blade to about the 12 o'clock position then turn on the ignition, then put your hand flat on the blade out near the tip (do not allow your fingers to curl around the edge of the blade) and flip it down toward the 9 o'clock position -- using a motion that carrys your hand and arm out and away from the arc of the propeller.

(All of which assumes you've got the tail-wheel chained to a fence- post and the slack pulled out... 'cause if you don't, it'll chase you :-)

So why 'Prop Orientation'? Because you need to know when a cylinder is coming up on TDC. And you need to know that relative to the blades of the prop.

VW engine fires once every 180 degrees. If you have a two-bladed prop you'd think it doesn't much matter how the thing is bolted on but it turns out, you do, and aligning one blade to #1 cyl is generally best. (Of course, that means the same blade is also aligned to #3 but I'll get to that in a minute.)

With a four-cylinder, horizontally opposed engine what you don't want is to have your signature cylinder in the same sequence on the same bank.

Clear as mud, right?

Go look at the VW's firing sequence: 1 - 4 - 3 - 2.

(Ed.Note: Cylinders 1 & 2 share the right-hand bank when facing the pulley-hub; cylinders 3 & 4 on on the left-hand bank.)

That means you don't want to have it fire on #2. Nor on #4. Because the next cylinder will be on the same bank... and the odds are, that cylinder won't have a full charge... because you just fired it's paired cylinder. What you do want is for the thing to initially fire on #1. Or #3. Because the next cylinder will be on the opposite bank. And -- trust me here -- the odds of the engine starting and continuing to run are about 100% better when the second cylinder to fire is on the opposite bank.

So mark one of your blades; the one that is going to fire on #1. Or on #3.

Now, you may have a problem with the 'clock'-related alignment if your prop-hub is drilled so a pair of holes aligns with the throws of the crankshaft. Because if you look at your prop, the usual arrangement is to have one of the prop's bolting holes aligned with the center of the blade. In theory, this should work okay -- and a lot of props are installed that way. (If your holes are so aligned, go aheady and try it.) But with a wooden prop you'll generally find the VW runs smoothest when the prop is not aligned with the crankshaft throws. And that presents something of a problem because you've only got six holes -- only three orientations -- to play with and only one of them is good for hand-propping... and it seems to have nodal points. (This is for the Type I engine. I don't think the T4 engine is any different.)

One solution is to use a prop extension in which the bolting holes are offset by thirty degrees. This gives you a bit more latitude. Or your prop, pitch, engine mount and crankshaft may present an entirely different torsional system than the T1 engine, which is what most of my experience is based upon.


4. Type of Ignition System (Finally!)

Hand-propped, even with an impulse coupling, a magneto puts out a weak spark. That means you'll need to use a narrow spark plug gap and a modest compression ratio, typically 7.5:1 or less, and those things can combine to make the engine notoriously hard to hand-prop. Not when everything is new and fresh but after it accumulates a few hours. Your plug-gap widens in use, as does the distributor air-gap, and the compression ratio falls as the engine accumulates wear.

At starting-speeds the stock Kittering-type ignition system (ie, as found in most vehicles up to about the 1995 model year) is vastly superior to a magneto. That's because the Kettering system delivers its maximum spark energy at the lowest engine speed. Makes things easy to start. But once its running, the spark energy drops steadily as the rpm increases, thanks to the declining amount of time the coil has to build up its 'charge.' (It isn't really a charge, it's just a magnetic field. But it's output is proportional to its strength and its strength is proportional to the amount of time so while it isn't electrically correct to say 'charge' it generally gets the idea across.)

A lot of folks -- especially the ones trying to sell you stuff -- will tell you that replacing the points with a transistor will give you a hotter spark. It won't. You've still got a Kettering ignition system and the output is still a function of the coil's current over time. But such systems do have a better wear factor and tend to give you a better spark because of it. That is, in the stock system your spark energy will decline as the points accumulate wear. Eliminate the points, you eliminate the wear, allowing you to enjoy maximum spark-energy the system can produce for a longer period of time.

Most modern-day ignition systems are some form of the Kettering System. The only ones that are truly different are Capacitance Discharge Systems, in which the points (or other trigger) discharge a capacitor through the coil. The advantage here is that the capacitor is charged with an invertor that may operate at voltages as high as 400, allowing it to re-charge the capacitor rapidly enough to allow the system to provide as much as 40,000 volts of spark energy up to speeds as great as 12,000 rpm.

Most of which is as useless as tits on a boar when it comes to flying Volkswagens :-)

But the bottom line is that that higher spark energy ensures more reliable starting. So if you're running points, replace them more often than you would in a car. And consider replacing them entirely, substituting some form of solid-state switch. Just be sure to not use any form of optical sensor. The VW distributor is not sealed and so long as you retain the distributor function (ie, the wires, rotor and cap) the central graphite button guarantees the optical sensor will eventually become obscured by oil vapor and carbon particles.


There's a few thousand things I haven't mentioned but the above should be enough to get you started. (Little play on words there, I suppose :-)


Ed.Note: In general, the factors discussed above must be taken into account when configuring any Otto Cycle engine for manual starting. In many cases Continental A-series engines with a reputation for being difficult to start need only to have the propeller re-oriented to make them start on the first flip. This is especially important with a 'Cub' on floats, where the engine must be started with one hand whilst balancing atop the starboard-side float.

Wednesday, February 21, 2007

Flying On The Cheap -- DOORSKINS

Flying On The Cheap – Doorskins

A 'door skin' is a 3' x 7' sheet of 1/8" Luan plywood. It differs from a regular four-by-eight sheet of eighth-inch luan ply because door skins are USUALLY fabricated using waterproof glue.

The simple test for waterproof glue is to boil a sample of the plywood. The regular stuff comes apart almost as soon as you drop the coupons in the water whereas the waterproof stuff can be boiled and dried several times before it starts coming apart.

Door skins tend to cost about 10% more than the regular stuff, partly because of the different glue but also because each sheet will have one perfect face. Typical example of the cost difference (as of 18 March 2006) is $6.98 for a doorskin (ie, 21 square feet) vs $9.79 for a 4x8 sheet of 1/8" luan (ie, 32 square feet). (Dixieline Lumber, Escondido, California)

The box stores tend to NOT carry door skins; most of their clerks won't even know what you're talking about but will try very hard to sell you whatever they do happen to carry.

Door skins have flown in Fly Babys, Volksplanes and a number of similar designs, albeit without benefit of clergy. When properly glued, carefully varnished and religiously maintained, the common door skin has proven to be a trust-worthy material for those of us who are flying on the cheap.


Sunday, February 11, 2007




The cylinders of Otto-cycle engines do not form a perfect seal. The piston rings provide a near perfect seal only during the Power Cycle when the pressure of the combustion process is above a given level. Depending on the fit of the parts and their state of wear, gases and finely divided liquids may cross the piston/ring/cylinder interface in either direction.

Gasses that escape past the piston rings or valves FROM the combustion chamber TO the sump or valve gallery is referred to as ‘blow-by.’ Some amount of blow-by is present in all Otto-cycle IC engines as a by-product of normal operation. The amount of blow-by is determined by a host of factors including but not limited to the number of piston rings, temperature differential across the system of piston, rings and cylinder, the fit of the parts, the, presence of valve stem seals, and the engine’s operating parameters, with more blow-by seen at elevated temperatures and high rpms.

Unless the valves are fitted with suitable stem seals, the intake manifold, exhaust manifold and combustion chamber is NOT isolated from the valve gallery. Blow-by that appears in the valve gallery tends to be extremely hot, easily capable of eroding valve guides and carburizing oil.

The crankcase of all Otto-cycle engines is vented to the atmosphere and meant to operate at atmospheric pressure.

Like all other fluids, the flow of gasses responds to a difference in pressure.

- - - - - - - - - - -


A basic goal of modern engine design is to eliminate blow-by at normal operating temperatures and engine speed. This goal may be attained through the use of shaft- and stem-seals, ‘Total-Seal’ type piston rings, additional piston rings and controlling the normal operating temperatures to within a narrow range.

- - - - - - - - - - - -

All of That and a VW Too

The above should give you some idea why the tree-huggers go zoo when they see an old Volkswagen chugging down the road. (Or flying overhead, too.) The VW engine was designed in the 1930's. It’s crankcase ventilation system consists of pumping the air in around the pulley hub and using a road-draft tube to suck it out, along with whatever it happens to pick up such as water vapor, oil vapor and combustion products.

As Volkswagenwerk AG bored & stroked the basic engine, the spew became worse; so bad they were eventually forced to close the road-draft tube with a flapper valve and use the carburetor as the source of suction needed to provide the pressure differential that ensured a proper flow of ventilation through the crankcase. But unlike modern crankcase ventilation systems, the inlet remained unfiltered and always open.

California’s effort to require Positive Crankcase Ventilation (PCV) on early bugs and buses came to an embarrassed halt after reputable testing laboratories showed the bureaucrat’s solution of add-on valves, hoses and temperature sensors more than DOUBLED the engine’s emissions.

All modern engines are fitted with shaft seals and any air entering the crankcase is filtered. Volkswagen owners who liked to play in the sand quickly discovered the practicality of such features and began fitting their engines with shaft seals, commonly called a ‘sand seal.’

Sealing the inlet to the VW’s crankcase ventilation system dictates the need for an alternative inlet, ideally one that is provided with a filter. After-market retailers provided a number of such devices in which the inlet function was transferred to the valve covers. The stock outlet was left in place. Unfortunately, the purpose of these after-market devices was generally misunderstood by VW owners, most of whom depend almost entirely upon Conventional Wisdom for their automotive information. Most VW owners as well as the ‘technical’ editors of VW-specific magazines ASSUMED the inlet fixtures were a new kind of OUTLET, disabled the stock outlet and ended up even worse off than they were before.

Since the customer is always right, the after-market suppliers merely shrugged their shoulders and began providing a number of shinier and more complex crankcase ventilation fixtures, all of which were eagerly purchased by mechanically naive owners, praised in the magazines and featured at the car shows and then installed incorrectly. Life is strange :-) In the mean time, real mechanics built their own inlet systems or installed a properly plumbed after-market device (there were several good ones) and got on with the race. Most everybody else began blowing smoke in a major way.

(Remember the joke about the idiot carpenter who threw away half the nails he took from his pouch because the point was on the wrong end? Remember how his boss explained that he shouldn’t throw them away because they were for the opposite wall? Keep it in mind as you read the following :-)

The usual cause for disabling the inlet to the VW engine’s crankcase ventilation system was the installation of a sand seal. On flying Volkswagens the most common cause was the installation of the Long-Taper sleeve-type propeller hub developed by Bob Huggins in the early 1960's.

The usual cause for disabling the outlet of the VW engine’s crankcase ventilation system was the installation of an after-market air-cleaner or dual carbs, in each case having no provision for the outlet hose. For flying Volkswagens the most common reason for destroying the crankcase ventilation system is because most people didn’t even know the Volkswagen HAS a crankcase ventilation system (!) (Must be for the other wall, right? :-)

The punch line is that once the crankcase ventilation system had been disabled Volkswagens began blowing their oil overboard. The cause of such behavior differs slightly between rolling and flying Volkswagens but the end result is the same. And of course, since the PERCEIVED problem was ‘blowing oil overboard’ the obvious solution was some kind of vapor separator; an oil recovery system. Which as you’ve probably guessed, the after-market retailers were quick to provide, along with boxes of nails for the Opposite Wall :-)

- - - - - - - - -

Wheat/Chaff, Men/Boys, Fact/Fiction, Oil/Vapor

One of the funniest lectures I ever heard in my entire life was a VW ‘expert’ telling a bunch of people that if your 1600cc engine was turning 4600 rpm, then it was producing exactly 53 horsepower. No exceptions. God Has Spoken.

Here’s the Real World version: The amount of power produced by your engine at ANY rpm is a function of it’s volumetric efficiency, which to save time you make think of as the position of the throttle. Throttle wide open? Then the cylinder is going to draw in a larger charge than if the throttle were barely cracked. Volumetric Efficiency defines the ratio between the maximum possible charge (100%) and how much the cylinder actually manages to suck in. The actual amount is sometimes referred to as the Effective Volumetric Efficiency or EVE. (I’ll get to ADAM, Seth and the boys in a minute :-)

(Have trouble getting a grip on this concept? Think about rolling down the road, lightly loaded, no wind, doing a steady 30 mph. (Do this on a chassis dyno, it will tell you that you’re putting out between seven and ten horsepower.) Then a Hill comes along (dreaded object for any VW owner). If you want to keep doing 30 mph you gotta keep pushing down on the accelerator pedal. If the hill is steep enough you’ll soon find the pedal flat to the floor. Your temperatures are starting to head for the red. The throttle is WIDE OPEN and you are only doing 30 mph. The engine’s rpm has NOT changed... but the engine is producing the maximum amount of power for those conditions. How much is that in horsepower? I donno... 25, thirty... around there. Truth is, horsepower isn’t what you should be concerned with; you should be looking at your head temps and your manifold pressure. But one thing I can guarantee you: If you just sit there, foot flat to the floor, watching your speed decay, you’re going to trash the engine. (And yes, Virginia, you can do exactly the same thing in your airyplane :-)

EVE for the air cooled Volkswagen ranges from about 10% at an idle to about 60%. (And that may help you understand why I’ve spent so many years trying to improve the volumetric efficiency of this particular power plant.)

You need to understand this because the problem of blowing oil is related to Maximum Output. The tricky bit is that Maximum Output may occur at less than 3,000 rpm in a flying Volkswagen but over 6,000 rpm in one with wheels. And if you really believe in equal power for equal rpm, in horsepower instead of thrust and the Tooth Faiery instead of slipping the kid a buck, you may as well toss this aside right now because nothing that follows will make any sense to you.

Maximum torque occurs at the point of peak volumetric efficiency. You may consider the former as the product of the latter. Peak volumetric efficiency occurs when the chamber is filled as full as possible under the existing circumstances, you light the fire and are rewarded with a specific impulse of the greatest possible magnitude and duration; lotta fuel means lotta fire; fire means heat; heat means pressure and the leg-bone is connected to the knee-bone.

Still with me? If so, you will see that the VW on wheels is blowing oil because of the high rpm, peaking temps and so forth. He’s a long, long ways away from his maximum volumetric efficiency but has managed to reach maximum output relative to rpm. The flying VW is rev-limited by the prop but the engine has reached its maximum output relative to that particular rpm. His volumetric efficiency is higher, as is his blow-by. And at that point his engine temps are liable to be well ABOVE anything you’ll ever see in a vehicle. (Why? Because John Thorpe is dead. The most popular of the flying Volkswagens are nothing more dune buggy engines with a fan on the nose, except they lack the dune buggy’s cooling system. The configuration of those engines as well as the public statements of the people selling them makes it painfully clear that they don’t know very much about aircraft engines, either in building them or cooling them, which John Thorpe did and taught to the rest of us.)

What it boils down to is a pair of engines lacking a proper crankcase ventilation system. One of the engines is maxed out for rpm, hotter than it should be, thrashing most of its liquid oil into hot vapor. It’s got some blow-by but it ain’t all that serious because the effective volumetric efficiency is right down near the bottom of the scale, not because the throttle is closed but because of the inertial mass of the fuel/air charge; at high rpms the cylinder doesn’t have enough TIME to suck in a big charge.

The other engine is maxed out for torque, running way over in the red, producing enormous quantities of blow-by, the combination of which has thrashed most of its liquid oil into hot vapor.

So now you want to separate the oil from the vapor.

Good luck :-)

You CAN separate oil vapor from air and I’ll describe the usual methods in a minute but the whole idea behind everything written up to this point was to help you understand that you’re buying a dead horse. Vapor separation AT THIS LEVEL is dealing with the symptom rather than the problem. What you should be doing is addressing the root problem, which is to PREVENT the vaporization of your oil. But the fact you’re here to begin with is good evidence that you are not mechanically adept; that you’ve probably bought an engine that came with the problems BUILT IN. And if you are not mechanically adept, when it comes to engines you are literally at the mercy of others; a victim-in-waiting with legions of slick hucksters eager to screw you out of your last buck. And your very life, in many cases.

‘Nuff of that; you won’t believe it until it happens, by which time it will be too late. So let’s go sort the wheat from the chaff. Or whatever.

- - - - - - - - - - - - -

Oil vapor is a generic term applied to everything from smoke to rain. True vapor, which is like smoke, responds best to condensation; chill it, the stuff turns back into liquid oil. Oil that has been divided into minuscule particles is still liquid oil. It may be hot and it may respond to cooling but so long as it is ALREADY a liquid the best strategy is to use its greater mass to cause it to coalesce into a FILM of liquid oil that you may then collect using gravity, centrifugal force, wipers (!!) or whateverthell you got.

So whatcha got? Can you drive a centrifugal separator? Prolly not.

If what you got is a bug, bus or airplane, the tactics you can apply to the problem are limited. When Porsche ran into this problem in the late 1950's (i.e., high revs resulting in excessive oil loss through vaporization) they added MORE OIL. Then they bit the bullet and put a vapor separator on the front of the blower housing. Hot weather, they still blew a lot of oil overboard but so long as they won their share of races nobody gave a shit. (You gotta be a Real Man to drive a sports car, right? :-)

The separator Porsche used was the column-type, similar to the one shown in the drawing (OIL_SEPARATOR_01). (As with most of the other drawings it is in .dc file format; download the free demo software to view it.) Mounting the separator on the front of the blower housing kept the thing reasonably cool. As the particulate oil collected on the baffles, it cooled and served as a cool-surfaced collector for the vaporized oil. End result was to reduce the oil loss by about 75%.

The outlet of the vapor separator must go to an area of low pressure relative to the inlet. On a carbureted engine the most logical low-pressure source is above the carburetor. If the vehicle is moving at a fairly high speed you can use a road draft tube; at higher speeds you can rig a venturi in the slip stream.

The oil separator should have the largest possible exterior surface in order to facilitate cooling of the captured oil. Fins would be a good idea. In an airplane you should consider an air blast tube.

Vapor separation occurs at ever level within the system. The plumbing runs to the inlet ports should have a constant downward angle toward the source. I’ve found half-inch or larger 3003 tubing to be the best stuff for the inlet plumbing runs. Hose makes suitable connectors and flex fittings. The liquid oil return line should use regular hose fittings.

The diameter of the column is up to the builder, as is the number of baffles. To fabricate the thing I simply cut a series of angled slots in opposite sides of the tubing. The baffles are trimmed to match the contour of the tube then welded in place.

The idea here is to force the vapor to turn a lot of corners. Oil, either as a true vapor or a suspended particle, has a mass several MILLION times that of a molecule of air. The air doesn’t even notice the corners, other than to spend a bit more time getting from Inlet to Outlet. The oil however sees the baffles as virtual dead-ends and can’t help but hit the wall. And that’s what you want. Once the oil hits the wall, you got it. Gravity takes over, the oil heads downhill, finds the liquid oil outlet and ends up back in the sump. You want to maintain an adequate head on the return line. Remember, this whole mess got started because the sump was allowed to get above atmospheric pressure. If you keep an adequate head on the return line there may be enough pressure in the sump to prevent the return of the liquid oil.

The effectiveness of the vapor separator is a function of its internal surface area, the number of baffles, the pressure differential and the temperature. To get more length you may have to lay the thing down. The tricky bit here is that if you place it too close to horizontal you will defeat the purpose of the baffles, turning them into oil traps. The thing will fill up with liquid oil, reducing the interior volume and you’ll commence blowing oil overboard again. So think it out, especially if the thing is going airborne. Not only must it be functional, it must be able to withstand whatever acceleration you plan to impose on your butt. (Hint: Go for at least eight g’s; you can do that much on a bad landing without even trying :-)

Like most other crankcase ventilation systems the one found on the early air cooled engines is a superb bit of engineering. (Indeed, just about everything on the basic VW engine reflects the results of evolutionary refinement during the production of twenty-two MILLION engines over more than half a century of use. ) The ratio of inlet to outlet accurately reflects accepted standards for such systems and is very similar to the equation applied to aircraft engine cooling systems. When you modify such a system, or when you add a vapor separator, you must pay the keenest attention to maintaining an adequate pressure differential across the system or device. The basic rule is to keep the outlet larger and at a lower pressure than the inlet. Temperature, the length of your plumbing runs, and a host of other factors will effect the outcome, as does where and how the thing is mounted. The point here is that what works for me may not for thee. Tinker with it. You’re the Mechanic in Charge.

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Couple of concluding remarks for the Instant Experts:

The use of a synthetic lubricant addresses only the heat-related side of the equation, in that synthetics typically have a higher boiling temperature. Excessive blow-by, itself an artifact of elevated temperature, and any rpm above an idle (when the engine is hot) is more than enough to give you a oil ‘vapor’ consisting of finely divided particles.

We’re talking fog here, okay? Ever seen a real pea-souper? According to NOAA the densest fog on the American continent is the so-called ‘Tule Fog’ that occurs in the Central Valley of California. And fog is water vapor, right? So how dense is dense? About 900 particles per cubic centimeter. (How bigz a centimeter? About... that big.)

So that’s water. And naturally occurring fog. (You can make a denser suspension using ultrasonics. Very tricky, kinda like cold steam.)

So what about OIL? Well... according to the U.S.Army’s kemical corpse, using simple procedures and light oils you can produce colloidal suspensions as dense as 4000 particles per cc. How? Same way you do with your VW engine: Just heat & stir :-)

So what’s the major factor, heat or rpm?

Heat. Oh, there’s a strong linkage but if you solve the heat problem a lot of the down-stream effects simply don’t occur.


More happy horseshit. If you’ve followed the instrumentation procedures advocated by Great Plains or John Monnet you’re measuring the temperature of the CRANKCASE rather than the oil it contains, and the temperature of the SPARK PLUG rather than the cylinder head.

Volkswagen knew what it was doing when it instrumented its industrial engines and measured CHT for its EFI systems. Measured at the spark plug your ‘cht’ could be as much as 150* F too low, compared to the measurement point recommended (and used) by Volkswagen, which is a specially cast lug on later model heads although they provided a Service Note explaining how to attach the CHT sensor to the lower exhaust stud on early model heads.

Same problem with the oil temp. If you just screw the sensor into a hole in the side of the crankcase, that’s the temperature you’re going to get. Volkswagen poked the sensor into the core of the stream of oil being sucked into the oil pump. On average, it reads nearly 100* F more than the temperature of the crankcase. And of course, the interior temps of the valve gallery runs about 100 degrees hotter than the average oil temperature.

This is another case of nails for the opposite wall. Wanna sell a kid a junker? Just diddle the speedo so it reads about ten miles per hour faster.

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Bottom Line Time

Blowing oil? Then find out why. There are three main reasons: Excessive blow-by at the rings. Excessive blow-by at the EXHAUST VALVE STEM. Improper sizing of the inlet-to-outlet ratio of your crankcase ventilation system.

A leak-down test will detect the first cause. The wiggle test will detect the second. Direct inspection will detect the third, assuming you know what you’re looking for, which is the TOTAL RESTRICTION offered by the outlet of the ventilation system. You could be running hose that is 3/4" in diameter, which should be more than enough. But if that hose is too long or if it has too many bends, the sum of its restrictions may cause the engine to ‘see’ only a tiny outlet.

Tiny outlet, the velocity goes up. When the velocity goes up so does its energy density, meaning it’s now strong enough to suspend & transport oil droplets of significant size, meaning you’re going to be blowing oil despite having a big hose.

The stock VW crankcase comes with a very effective oil separator built-in. Pull the dynamo tower and you’re looking at it. You can improve its effectiveness by stuffing the space under the dynamo tower with coarse metal mesh, such as a bronze or copper ‘Chore Girl’ pot scrubber. Not real handy as an oil-filler port since all new oil has to filter its way down through an inch of pot-scrubber but it works a treat at keeping the blow-by dry.

In the attached drawings the top of the column is often made to accept a removable valve-cover vent, like you see on an old Chevrolet Six. The cap contains a wire ‘filter’ that can be washed.