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alpinelakespilot2000

Well Known Member
DWG Op-27 shows the oil breather tube to be cut at an angle that looks to be either facing aft or parallel to the exhaust. However, I've read a number of threads where people argue for cutting the angle such that the opening faces fwd. The picture below shows what I've done so far... should I change the direction of the bevel?
Thanks.

 
It should face forward. What you want the breather to do is provide ventilation for excess pressure inside the crankcase, not create a suction that vacuums stuff (oil droplets and spray, for instance) out of the crankcase.
 
Kyle,

Can you clarify for me? (I need to do the same thing.)
Steve's pic shows the cut basically parallel to the exhaust. Are you saying the tube opening should be more forward? ...causing air flow to basically blow into the tube?

Thanks,
Sam
 
I tried all sorts of angles and still had blow-by. I ended up fabricating and installing an air-oil separator (see Bingelis for details - they are outrageously expensive for a tin can with some steel wool!) and the problem went away.

greg
 
TX7A said:
Kyle,

Can you clarify for me? (I need to do the same thing.)
Steve's pic shows the cut basically parallel to the exhaust. Are you saying the tube opening should be more forward? ...causing air flow to basically blow into the tube?

Thanks,
Sam
Click to expand...

Yes, the tube should be cut where the relative airflow blows into it.
 
The Rocket guys no longer end the pipe at the exhaust, but rather bend it and extend it out the bottom of the cowl like the exhaust pipe itself. This has greatly reduced the tendency of the vent line to pressurize the engine case and cause oil leaks elsewhere. Remember, the purpose of this line is to relieve the pressure in the case and provide a place for oil vapor to escape. Putting it in a high pressure area is not a good idea. As long as you extend it out next to the exhaust pipe, it stays warm enough to keep it from icing over.

I made this change after Tom Martin experimented with it and it immediately stopped a couple of nagging oil leaks I had in the front seal and accessory case.
 
Breather Hose Cut

Hmmm......Being a buyer, not a builder, I have an A&P do my annual condition inspection and his theory is a forward facing angle pressurizes the crankcase and helps to induce small nagging leaks.
Seems to work, since installing a new breather hose with an aft facing angle just above the left exhaust, my belly is a whole lot cleaner than it has been for a long time.
This appears to be one of those questions that fits in right along with "which is better for me, a 6 or a 6A, 7 or a 7A, etc."
 
A hole in the line about 3/4 the diameter of the tube located within the last 10 inches that will eliminate suction or pressure. Crankcase filter material wrapped around the tube and held with pull ties keeps the mist inside.
 
alpinelakespilot2000 said:
DWG Op-27 shows the oil breather tube to be cut at an angle that looks to be either facing aft or parallel to the exhaust. However, I've read a number of threads where people argue for cutting the angle such that the opening faces fwd. The picture below shows what I've done so far... should I change the direction of the bevel?
Thanks.
Click to expand...

Steve, mine looks identical to yours. Seems that the replies so far have been mixed, faced forward, faced aft. I do get lot's of oil coming out the tube. Once the oil level stabilizes around 7.25 quarts it does stop (seemingly). I don't see how our installation is getting much Ram air . I do see it having some neg. pressure.

I am all ears as to some good suggestions on this.
 
apkp777 said:
Steve, mine looks identical to yours. Seems that the replies so far have been mixed, faced forward, faced aft. I do get lot's of oil coming out the tube. Once the oil level stabilizes around 7.25 quarts it does stop (seemingly). I don't see how our installation is getting much Ram air . I do see it having some neg. pressure.

I am all ears as to some good suggestions on this.
Click to expand...
Thanks Tony. I agree that there doesn't seem to be a consensus. And Van's must have some reason for drawing it the way they do. (?)

That said, I think some of your problem may be that you have too much oil in your 320. I've read a bunch of threads that suggest anything more than about 6 quarts just gets blown out anyway. For the break-in maybe more is better, but you might do some research to see if 7.25 is too much oil after your break in is done. (Check my numbers--I'm going off the top of my head.)
 
alpinelakespilot2000 said:
Thanks Tony. I agree that there doesn't seem to be a consensus. And Van's must have some reason for drawing it the way they do. (?)

That said, I think some of your problem may be that you have too much oil in your 320. I've read a bunch of threads that suggest anything more than about 6 quarts just gets blown out anyway. For the break-in maybe more is better, but you might do some research to see if 7.25 is too much oil after your break in is done. (Check my numbers--I'm going off the top of my head.)
Click to expand...

Yeah, 7.25 is too much, but I am just breaking in the engine and fighting high oil temps. It'll blow about a quart every 20 hours.
 
f1rocket said:
The Rocket guys no longer end the pipe at the exhaust, but rather bend it and extend it out the bottom of the cowl like the exhaust pipe itself. This has greatly reduced the tendency of the vent line to pressurize the engine case and cause oil leaks elsewhere. Remember, the purpose of this line is to relieve the pressure in the case and provide a place for oil vapor to escape. Putting it in a high pressure area is not a good idea. As long as you extend it out next to the exhaust pipe, it stays warm enough to keep it from icing over.

I made this change after Tom Martin experimented with it and it immediately stopped a couple of nagging oil leaks I had in the front seal and accessory case.
Click to expand...

This is an interesting idea Randy rasies, and the theory makes lots of sense regarding oil leaks.

The logic behind doing it the other way was explained (by me) in an RVator article from 2001 or 2002 where a bunch of oil puked through my breather because of a combination of two factors:

1) A bevil cut to create a vacuum on the crankcase breather.

2) A dipstick that wasn't screwed in properly (my fault).

In a 15 minute flight, this combination caused over a quart of oil to suck through my engine. To me, that's the kind of thing that could have resulted in a catastrophic result on a longer flight.

I realize that I've left the dipstick loose exactly once in 15 plus years of flying, so the odds of this happening again are small. However, by putting the bevil into the wind I think I've removed one scenario from the long list of items that could cause an engine failure.
 
I had a little seeping in the front seal that stopped when I angled the breather tube so that it was not being pressurized. I now have it right over the exhaust.
 
gasman said:
A hole in the line about 3/4 the diameter of the tube located within the last 10 inches that will eliminate suction or pressure. Crankcase filter material wrapped around the tube and held with pull ties keeps the mist inside.
Click to expand...


This, and 7 quarts max solved all of my oil to belly problems.......... And my tube is square cut about 1" under the firewall.
 
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Engine216.jpg


I cannot view the picture that started this post probably because the site is banned from my work Internet. Anyhow, here is a picture of how I initially installed the end of my oil breather tube. This installation resulted in my crankcase being pressurized and causing oil leaks. FWIW.
 
f1rocket said:
Engine216.jpg


I cannot view the picture that started this post probably because the site is banned from my work Internet. Anyhow, here is a picture of how I initially installed the end of my oil breather tube. This installation resulted in my crankcase being pressurized and causing oil leaks. FWIW.
Click to expand...

Hi Randy,
Do you have a picture of your current setup? I'm going to re-do my oil breather line and am trying to figure out EXACTLY how to do it.

I've got oil leaks in my engine and I believe they're at least partially caused by my current setup. I didn't have the right hose and it's making a sharp bend around my oil filter...I just noticed it had a small split in it, so possibly this is causing my case to be over pressurized?

Either way, I want to re-do the setup so that it stops the leaks I have (hopefully). Can you tell me what type of aluminum tubing you used and how far aft you terminate it by the exhaust? Also, do you have a relief hole drilled in the line somewhere?
 
Sorry, but I don't have a current picture and I no longer own the airplane. All I did was remove the tube in the picture, shorted the hose a couple of inches, and then took another piece of tubing and bent it using a conduit bender about 45 degrees to point it out the back, between the two exhaust pipes. I added a couple of cushion clamps to hang it off the bottom of the mount. As long as the end of the tube sticks out into the airstream past the end of the cowl, it'll work. I just used a piece of conduit from the airplane parts isle at Home Depot. I didn't see a need for a "whistle slot" or hole in the tubing since it is cuddled in between two hot exhaust pipes. I don't think there's much of a chance of ice buildup in this location.
 
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I am not understanding how the breather tube can cause an oil leak? Can someone help me with this? Are you suggesting that the original poster's picture is showing the breather tube cut in such a way that it will produce an oil leak?
 
The flow of air though the engine compartment will pressurize the crankcase via the vent line. This causes oil to exit the case at various locations. Yes, it causes leaks that otherwise are not there once the pressure is relieved. This would happen on brand new engines that Bart had built and tested. I always wondered why they couldn't assemble a Lycoming that didn't leak until Tom Martin let me in on this secret. Once I made the change, all my leaks stopped. They weren't big leaks, just enough drops of oil to cover everything with a fine coating that attracted dirt and dust.
 
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Crankcase pressure

The Crankcase breather should not have too much suction (lose oil) or pressure (engine leaking oil) . For the best answer best to use the modified oil filter cap with an filling on it connected to an airspeed indicator in your cockpit to measure pressure (lycoming has a spec somewhere on this) make sure you are in spec in level flight, move breather to adjust
Peter
RV6
 
f1rocket said:
The flow of air though the engine compartment will pressurize the crankcase via the vent line. This causes oil to exit the case at various locations. Yes, it causes leaks that otherwise are not there once the pressure is relieved. This would happen on brand new engines that Bart had built and tested. I always wondered why they couldn't assemble a Lycoming that didn't leak until Tom Martin let me in on this secret. Once I made the change, all my leaks stopped. They weren't big leaks, just enough drops of oil to cover everything with a fine coating that attracted dirt and dust.
Click to expand...

I have the same oil leaks you describe. It looks like there's ten drops that just bounce around in the engine compartment then hide when I open the oil access door. I have yet to see a single drip, but there's clear evidence of an oil weep/seep/leak.

I am willing to cut my breather tube, but I am just having trouble figuring out how to make it effective without connecting the ASI to the dipstick cap. Purhaps, adding a piece of hose to the end that I can lengthen/shorten and note the results.
 
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