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Crankcase breather
 | 2011.10.07:
The way Van's handled the crankcase breather sucks. They have a
straight 3/4" nipple on the engine pointed right at one of the
engine mount tubes an inch away. To clear the engine mount, they
then go to a 90° elbow cut from a NAPA radiator hose. This hose
is not meant to withstand hot oil, and evidently indeed it does not
(turns soft and sticky and has to be replaced every few months).
From there they go to a 5/8" aluminum tube, pre-shaped by Van's
with a 3/4" expansion on top, and curves down below that don't
quite get it around the lower tubes of the engine mount, and only
flimsily supported by a single adel clamp... Total crap.
A lot of builders have made various changes to the breather
installation, some seemingly good, others less clear... I
decided to just take a fresh look at the problem and do a clean sheet
design. Here's what I came up with, which at least so far looks
really good:
Start with a 5/8" 45° nipple (AN818-10D) on the engine.
This points the nipple more aft such that a straight line from it
clears the engine mount. Duh! From there, slip on a
5/8" inner diameter (-10) MIL6000D hose, which is actually
specified to withstand hot oil. The length of hose, which gives
the necessary elasticity to accomodate relative motion between the
engine and the firewall, arches over toward the firewall where it
slips over a 5/8" aluminum tube. The aluminum tube is
shaped to clear the engine mount at the bottom, and is firmly secured
to the airframe with three adel clamps -- two to the firewall and one
to the engine mount near the bottom. Finally, it vents overboard
in the cooling air exit between the exhaust pipes, where it will have
warm air flowing across it. And just in case it still manages to
ice over, I also cut a "whistle slot" in the tube about 6
inches above.
45° nipple on the engine, and aluminum tube on the firewall:
MIL6000D hose:
Aluminum tube snaking its way around the bottom of the engine
mount. Also shown is the whistle slot:
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