![]() |
I have found that the location of the NACA vents inline with the cowl split will does have an effect on smells. Several years ago the GAMI folks had a video of a V35 Bonanza where they tufted the inside of the cowl and found that some of the air flows forward along the crankcase. In both my RV-6 and the one I fly now it can be in the dead of winter, 20 degrees OAT and warm air will come thru the NACA vents. So really this is a problem related to the NACA vent location, not necessarily the breather exit.
I overhauled a 300hp angle-valve 540 a couple of years ago that had two cylinders with broken rings and did not find any appreciable amount of liquid oil flowing from the breather tube or on the belly. When I pulled the cylinders pieces of the rings fell on the floor. What I suspect here is since the breather hose is uphill the oil mist is settling on the walls of the hose and flowing back into the engine. Also for the record I've found that there are two different types of blow-by. Crankcase blow-by due to windage in the case and valve blow-by where excessive guide wear causes oil to be sucked into the combustion chamber and burned. Either way a drop every few revolutions adds up to appreciable oil consumption numbers. Many new automotive engines have windage trays and so do the 300hp 540's. The tray is there to reduce foaming and adds extra area for oil to settle on. |
Bob, I was thinking more of a worst case scenario like a major detonation event. You are right, simple broken rings won't add much crankcase pressure. I have witnessed a piston failure like this in an IO360, but it took an ugly set of circumstances to get to the failure. Sure did blow the oil out the vent though.
![]() John Clark ATP, CFI FAAST Team Representative EAA Flight Advisor RV8 N18U "Sunshine" KSBA |
Like Joe said, MIL-6000 is good, a lesser expensive alternative is industrial spec 100R6 hose. It is oil resistant, but doesnt like a sharp bend radius. IF you have use a molded hose for routeing purposes, try a silicone heater hose---if you can find them. Ultimate would be convoluted teflon.
Tom |
Just terminate breather line above exhaust pipe-----my RV-8 has had it for 15 yrs.----works well, lasts a long time---John Fleurent----RV-8(SKY GODDESS) First flight 1998
|
Gum Creek
Hey John.....thread jump for a second.........saw some guys over the weekend at Gum Creek Airport in Roopville Georgia that knew you. A great morning for me.
David Watson 49FD |
Alt Breather-Some Results
Thanks for all the thoughts and hope someone has DATA for a couple questions that have now surfaced:
-The hose is a temporary solution and will be replaced. -The filter is bone dry. -I also believe the oil misty air is slowing down in the hose with the filter allowing free flow and the oil condenses and drips back to the breather port. -There has been no leakage detected. -The underside is not oily. Does anyone have measured delta pressure data for my filter location and various point around the engine, i.e. on top where cooling flow enters, near the oil sump, near exhaust pipe exit? The idea that my filter location is high/higher pressure is worth investigating. Based on my experience and what is reported as normal budging oil doors, the volume between the FW and engine is certainly higher than free stream. Wonder if it gets lower, like free stream at the cowl exit without Dan H. mods for exit area reduction? |
Quote:
|
Quote:
Here are pressure values taken with a smaller-than-stock RV-8 cowl exit (but not as small as the one I use now). All pressures in inches of water: ![]() A healthy Lyc might have a breather pressure in the 1" to 5" H2O ballpark, so yes, you are probably running a higher than normal case pressure. I think comments about the possibility of dumping oil into the cowl following piston failure are valid. I'd want it breathing overboard somehow. Quote:
|
Gave up-Oil Separator
My home grown system did about the same as the stock breather system, it allowed the oil vapor to breathe but eventually the filter was saturated and then oil mist on the firewall.
Just installed the complete Anti-Splat system with the clamp on check valve. Can't wait to be able to run more than 4 quarts without it blowing out the vent. Got lucky and was able to drill the exhaust without removing the lower cowl. ;) |
| All times are GMT -6. The time now is 08:21 AM. |