A65 Crankcase Vent

gusc · Post by **gusc** » Sun Sep 10, 2006 22:58

After getting my new 7AC Maint Manual I noticed that the crankcase vent goes straight down from the case elbow and terminates at the right rear a good 8-10" from the firewall and about the same distance from the cowl bottom??

This is nothing like I expected, I changed mine from the left to the right recently but I terminated it just an inch or so from the cowl bottom?

We had a pretty long string going on this subject a while back but nothing like this manual drawing was discussed.

Do any others have A65s with the vent like in the manual? I'm not sure I want to change it but on the other hand I don't see any problem having it as shown in the manual.

Ron Babos · Post by **Ron Babos** » Mon Sep 11, 2006 16:46

gusc: The only difference will be where the oil ends up, boot cowl or axel tube. Not all that important. Mine is about 1/2 inch below the boot cowl/firewall joint and there is a slight smear of oil after an hour. The original location as you mentioned is no cleaner if the Champ at the club is any example and I have seen ice hanging off of it back there on occaision in the winter. This is where a second opening comes in handy

Ron

MikeB · Post by **MikeB** » Mon Sep 11, 2006 21:40

During the summer months, I have a hose that I shove over the end of my breather tube and it ends just over boot cowl exit. I know some say that you can get a venturi effect which will suck oil out, but don't believe I've ever seen it. During the winter, I take the hose off so the breather exits higher in the boot cowl. Makes for some oil mess, but not bad (mostly after I shut the engine down for the day). It also have a 'whistle' hole higher up near the block exit.

When I was a young diesel mechanic (many years ago, I might add) it was common for truckers to put a heater hose over their crankcase breather to keep the oil drips off their engine blocks and prevent smelly blowby fumes in their cabs. Occasionally, one of these would ice shut in the winter after the engine was shut down and blow oil seals and valve cover gaskets when the engine was restarted.

Mike

gusc · Post by **gusc** » Mon Sep 11, 2006 22:17

The one in the manual appears to be rubber, metal, rubber, metal from the top down. The closest to the exhaust pipe seems to be metal. Maybe the idea of that was to prevent ice.

In any case, it makes sense to have rubber at the end and inside the cowl for cold weather. We don't have a lot of that stuff down here in the South though! The whistle hole makes sense even in warm climates because of what we call dirt dobbers (mud wasps) here. One caused me to total my Stinson when it plugged the fuel tank vent. They love pitot tubes also.

I know of a Cessna 180 which sucked the oil out when the owner decided to extend the vent about a foot so he would have a clean belly. I think a lot of that was caused by the much higher speed too, a Champ is not going to have this problem! I was very careful about that when I rerouted my Navion vent and added the little worthless oil separator.

Dennis · Post by **Dennis** » Tue Sep 12, 2006 09:03

Gus,

I routed mine along the engine, slightly up hill, through the rear engine baffle to the firewall. Used a premolded NAPA 90* hose, into one of the worthless air-oil separators mounted on the firewall. It was laying around, might as well use it. The tube out the bottom extends about 4 " below the belly. I figure once flying I can cut it to "proper" length, if necessary. As far as I am concerned, speed is less inportant than cleaning the belly.

Checking today on the printing capability.

Dennis

gusc · Post by **gusc** » Tue Sep 12, 2006 21:53

Dennis,

I started to route mine up also as I was taught and had done on previous airplanes, but decided that I wasn't going to try to solve a non-existant problem.

Then I got my manual and it shows the vent going straight down so I'll leave it that way for now.

The only question in my mind now is the vent termination position. Since it vents almost no oil I may cut it inside the cowl as shown in the manua but I need to fly it more before I reach that decision.

My concern about the vent hanging down is not drag but the possibility of slipstream suction pulling the oil out of the crankcase. As I said, I think the Champ is too slow for this ever to happen. A Cessna 180 at 150 MPH is another matter.

I have one of those old huge type oil separators that was used for wet vacumn pumps. I may us it if needed but I won't waste any more money on those little ones.

Dennis · Post by **Dennis** » Wed Sep 13, 2006 17:50

Gus,

I am speculating but I would suspect that, with the ice hole above the outlet and air much less viscous than oil, that slipstream suction, if any, would be satisfied with air from the ice hole above the outlet. As I said, just speculating. When I fly mine, I will be closely watching oil levels and the belly.

BTW, I got the left wing put together and have started on the right wing.

Dennis

gusc · Post by **gusc** » Wed Sep 13, 2006 22:28

Dennis,

Good point, I hadn't thought about the ice hole. The C180 didn't have one.

gusc · Post by **gusc** » Wed Sep 13, 2006 22:38

Dennis,

We're headed out of town for about a week and I'll have no access to a computer.

Maybe I'll have the rudder repaired by the time you finish the wing!! I'll fly over to see you on the test flight.

Dennis · Post by **Dennis** » Thu Sep 14, 2006 15:47

Gus, give me a hollar. Love to see your "new" plane.

Dennis

Dennis D'Angelo · Post by **Dennis D'Angelo** » Sat Sep 16, 2006 23:18

Dennis/Gus:

My 7AC has the crankcase vent tube exiting 1/2 inch below the boot cowl lip with the ice hole located above the lip in the warm air exiting the cowling. I have had no icing problems and very little oil residue.

Dennis is correct in that any pressure differential caused by the venturi-effect is equalized through the ice hole.

dd

"The fastest way between two points is? Full throttle."