REFLECTOR: Oil consumption

Scott Derrick scott at tnstaafl.net
Sun Feb 24 15:37:37 CST 2013


Breather into exhaust.

You may need  backfire prevention if you plumb the breather way up 
inside the exhaust. I've seen some longezs that had it between cylinders 
which possibly, a backfire could cause a momentary pressure rise in the 
crankcase pressure.  I think its an OWT to claim you could ignite the 
gas. Its got way to much exhaust(ring blow-by) to lite off.

The Velocity exhaust made by Custom Aircraft puts the breather near the 
exit, downstream from the 3-into-1 connection and thus eliminates any 
possibility of pressurizing the crankcase. Instead if you backfired it 
would lower the pressure in the case.

I've attached a diagram.  Mine is actually on the other side of the engine.

I think you are right that the breather fitting does increase the 
blow-by oil a bit, because you are scavenging(sucking) the toxic gases 
out of the crankcase. Makes your engine run much cleaner. Since 
installing the breather scavenge fitting I think I went from 16-17 hours 
per quart to 15 hours per quart.

Rumor has it from the auto racing crowd you increase your HP output by 
scavenging the breather tube, which lowers the crankcase pressure and 
thus reduces the internal friction.

Scott

-------- Original Message --------
Subject: Re: REFLECTOR: Oil consumption
From: vance atkinson <nostromo56 at tx.rr.com>
To: reflector at tvbf.org
Date: 02/24/2013 01:50 PM

> It doesnt have to be that way.  Im on my 4 set of cylinders in 26
> years.  First two were remainufactured. Next set was from Superior. And
> the last set was from Lycoming and they were new.  I use 1 qt of oil
> between 25 hour oil changes. I have a Lyc. 0320.
>
> The first three sets of cylinders got about 10 hours per qt on new oil
> and 6 hours on dirty oil ( just before oil change). Problems with the
> first 3 sets wound up being mostly valve problems..... So now I'm lucky
> to have the std steel cylinders that I got from Lycoming preforming as
> well as they do.
>
> If you decide to run your breather into the exhaust, be careful because
> if you get a backfire, you could have a problem.  Use an automotive anti
> backfire valve for insurance.  Also when that set up was the rage years
> ago, some of the guys found their oil consumption going up as it helped
> suck extra oil out instead of a normal amount, but on the positive side
> it got rid of any oil leaks the engine had as it created enough vacuum
> to clean them up.
>
> Vance Atkinson
> EAA Tech and Flt Advisor
>
> On 2/23/2013 9:08 PM, Scott Derrick wrote:
>> airplane engines as a whole burn and blow oil overboard. Its part of
>> their 1950's design.  Auto engines have evolved to not burn or blow
>> oil.  Airplane engines have not evolved in that area to a large degree.
>>
>> Continental by and large burns or blows less oil than Lycomings. My
>> Cont. io520, needs about a quart every 10-15 hours.  If I run it
>> hard(high rpm) it needs closer to 10, if I run it easier it tends
>> towards 15. It blows more overboard at high rpm.
>>
>> Running your breather tube into your exhaust system, burns and blows
>> the oil away from the cowl.  A rutan trick that is an excellent
>> solution to the oily cowl.
>>
>> Scott
>
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