On Oct 20, 5:45*pm, wrote:
This ain't rocket
science and you aren't building a space shuttle. Gravity flow to a
carburated engine is the safest and most reliable fuel feed possible,
until you are attacked by Feherenghi using anti-grav phasers.
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Agree.

As with most engines, the VW fuel pump is driven at cam speed but it
is NOT driven off the cam shaft, a significant difference with regard
to its mechanical durability. It is driven off the crankshaft via its
own gear-train. The pump is a two-chamber type in which the
mechanical input serves only to extend a compression spring. The
spring is then free to retract, the amount of retraction determined by
the quantity of fuel drawing into the lower chamber during the
extension cycle. In effect, the pumping action is performed by the
spring rather than by the engine.

Mechanically, the pump is isolated from the engine by a push-rod that
is actuated by a pinion gear. The flexible diaphragm that makes up
the floor of the lower pumping chamber has a useful service life in
excess of 1000 hours, the push-rod slightly more than that. Output
pressure is typically between 8 and 16 ounces, depending on the
spring. Any flow-control valve, such as the ball-valve in the stock
Solex carburetor, which typically has a pressure between 8 ounces and
two pounds is sufficient to shut off delivery. However, any fracture-
failure in the delivery circuit will cause the pump to spray gasoline
in all directions. Wear in the push-rod is reflected by its length
which may be meausred by removing the pump (two studs). Volkswagen
provided three pump push-rods of different lengths.

Failure of the flexible diaphragm offers a bit of visual warning in
the seepage of fuel at the parting line of the pump. This is only
valid for the early model, rebuildable fuel pumps, which is what I
prefer to use on my VEHICLES. In an airplane I'm more comfortable
with a gravity-fed system, even if that includes a header tank in the
fuselage.

The push-rod actuates a bell-crank in the base of the pump body, which
is a white-metal casting. The bell-crank's pivot bears on the casting
without provision of bushings or bearings. In a high-time pump it is
common to see the bearing-holes worn to an oval. The pivot itself is
held in place by a cotter key (early) or snap-ring (late) which is
also subject to wear. The pallet of the bell crank calls for periodic
lubrication with axle grease, maintenance it seldom sees when the
vehicle is maintained by the typical owner. (I believe the service
interval was every 12,000 miles or annually but I'd have to check the
Factory Service Manual. I do it about once a year and have never had
a mechanical failure due to lack of lubrication. I have had the pivot
and the fastener break.)

In my opinion, each builder is responsible for answering such
questions for themselves. I can offer an opinion and may provide an
example to support it but ultimately, that's the limit of my interest
and responsibility; I can always refuse to ride in the thing. (And
have, on several occasions.) Personally, I don't care for pumps and
would eliminate them if possible, especially if they are engine-
driven. The next best choice would be an electrically driven pump (or
any number of them) located where a failure would not douse the engine
with gasoline. Even so, at best all this would do is reduce the risk
of an IN-FLIGHT fire. Following a crash or bad landing, there is
usually some amount of fuel at the scene regardless of where the fuel
tank is located and no matter how the fuel is delivered to the engine.

-Bob Hoover