Roee Kalinsky's RV-7A Project

Crankcase Breather
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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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Copyright © 2003 Roee Kalinsky
Last modified: October 30, 2011

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