The International Cessna^® 170 Association

Just had my 1948 in for its annual inspection. I have been leaking some oil lately. The I&A did 2 things to address the oil leak. 1) Replaced the gasket between the starter and accessory case as much of the leak was coming from there and 2) Extended the crank case breather tube about 2 inches below the below the bottom of the plane and drilled a small hole about 6" up the tube from the bottom, on the rear of the tube. The I&A said this was a recommended fix to the breather tube icing up at the bottom and causing backpressure in the crankcase forcing more oil out of all the places it could come out. I don't see any harm in this but has anyone heard of this before? This I&A has a well known shop here in Alabama and does a high volume of work on older aircraft, including full restorations, etc. so in the past he has always known what he is talking about.

Curt

In colder climates we always vent the breather tube somewhere. Just make sure everything upstream of the vent keeps nice and warm. The consequence of a frozen-shut breather can be to blow out the front seal.

The hole in the breather tube is part of AD 82-07-02 to relieve pressure if the end of the tube would become plugged with ice. If the tube clogs and there is no relief the front crank seal can blow out causing rapid oil loss.

Don't know about extending the tube.

Thanks, guys. Looks like the I&A did the right thing. Don't know why he didn't catch it on the last annual though. Maybe he looked harder this time as I asked him to fix the oil leaks.

Curt

82-07-02 covers aircraft with Lycoming conversions, but putting the hole in an O-300 or C-145 vent tube can't hurt.
brad

During my last annual, my mechanic and I drilled the vent hole in the breather tube as outlined in the AD. Since then I have noticed an oil mist on the cowl which seems to be coming from the drilled hole. As a result, I taped it closed.

Robert Eilers wrote:During my last annual, my mechanic and I drilled the vent hole in the breather tube as outlined in the AD. Since then I have noticed an oil mist on the cowl which seems to be coming from the drilled hole. As a result, I taped it closed.

Robert,
What engine do you have? I have the hole in my O-300 and Dad has one in his C-145 Both with no ill effects.
brad

Robert, perhaps your breather relief-vent is improperly accomplished.
It should be reverse-relieved, i.e., any exiting gases should not exit the tube unless the end of the tube is blocked. There are two methods to accomplish this: Cut a 1/2" slit approximately 10" from the exit-end of the tube, as if to completely sever the tube...but stop cutting when only 1/3 of the tube diameter is cut. Then depress (slightly collapse) the tube wall at the upper side of the cut so that the slit should remain invisible to any flowage of gas/oil....<or>... drill a 1/4" hole in the wall of the tube approx 10" from the lower end of the tube. Then, with the drill still inserted in the hole just drilled, but with no rotation of the bit, raise the drill-bit motor-end upward so as to depress the upper edge of the hole inward towards the tubing center. This is make the hole invisible to any flowage of oil mist flowing within the tubing.

Thanks George - I failed to raise the drill after the hole was drilled and indent as you described. I'll give it a try.

Brad you are right about 82-07-02 ad being for a Lycoming which I never noticed before.

But I was sure there is an AD or at least SB covering the same thing for the 0-300 and in fact my Cub and any engine installed in it. Or perhaps this just has become standard preventive practice and I've seen it on many aircraft an attributed it to an AD.

Bruce,
I can't think of any SB, off the top of my head that calls for the breather mod. I think that it has just become a precautionary thing that a lot of people have opted to preform. I realy can't see where it could hurt
brad

Toward the bottom of this website http://150cessna.tripod.com/c150o200ainsp.html they talk about using a breather from an aerobatic C-150, TCM p/n 633182 to reduce oil lose through the breather. Any thoughts on using this on the O-300?

n2582d wrote:Toward the bottom of this website http://150cessna.tripod.com/c150o200ainsp.html they talk about using a breather from an aerobatic C-150, TCM p/n 633182 to reduce oil lose through the breather. Any thoughts on using this on the O-300?

Gary, this mod has been discussed several times here on the forum, but the 633182 elbow is $338 and that is the "discounted price" from Hill Aircraft. It also has been suggested that you could braze a tube to the current elbow. I've been waiting for someone else to do this mod to see if it is worthwhile.