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Breather tube p/n

Desert Rat

Well Known Member
Can somebody with an RV14 take a quick peek at their parts stash and tell me the diameter of the aluminum breather tube that runs down the firewall?

Alternately, if anybody has the plans handy, I can likely look it up if I know the correct part number.

The RV7 solution seems pretty clunky plus it has the potential issue with the heater hose elbow that has been discussed here a bunch so I'm looking at crafting something from scratch.

The factory part for the RV7 starts at 3/4" but chokes down to 5/8" as soon as it makes the transition from rubber to aluminum and I'd like understand if the "official" one for the IO390 is the same or if it's 5/8" or 3/4" for it's whole length.
 
Breather

I did not like the 7 breather tube plan. The hose provided is way bigger than the crankcase breather. The curved tube gets in the way. Mine is modified.
First fill it with sand. Straighten it. Cut off the flared end.
Or just buy a section of tubing.
Buy one of these.
The hose fits both the vent fitting and the tube and it's a power steering hose so it's made for oil. I cut mine so it rises as much as possible. Curved portion is nearbthe firewall.
The bottom of the vent tube was bent so it's directlt over the exhaust with an angled tip. About 6" above the tip, drill a hole on the forward side of the tube about 3/16". Flip the drill bit, insert and bend the bit upward. That way the oil will run down inside the tube and if it freezes over it can still vent.
This way, the hose can be easily removed for a bit more access.
 
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I appreciate the link Larry- But basically, my question is this: On my IO390 The fitting coming off the accessory case is 3/4". The hose vans sources for their finishing kit (which I didn't buy) is 3/4" but immediately downstream of where it mates to the downspout, the tube shrinks down, presumably to something in the ballpark of 5/8"

Does anybody see a problem if I change that fitting out for 5/8" and just go with a simple 5/8" mil spec hose or the power steering hose that Larry provided above into a 5/8" downspout?

It seems obvious that would work, but if it was that simple, I don't understand why vans cobbled together the solution they provided.
 
I have the 390 in my 7, about a year ago I changed out the 3/4” fitting for a 5/8” fitting and have the hose Larry mentioned. I noticed no difference in engine operation with the change.
 
Thanks Don- It stands to reason that it really wouldn't matter, but I wasn't 100% certain that the additional bore of the bigger pistons flailing around in there might like a bigger vent pipe, i.e. why Lycoming shipped my 390 with a 3/4" fitting installed.
 
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