Oil Breather "Fixes" on Continental Engines

The following, based on an article in the November/December 2001 Issue of Cub Clues, the newsletter of the Cub Club, is provided as a courtesy to M-18 owners by the Mooney Mite Site.

Nearly every owner of a Continental-powered aircraft has had this problem and is looking for the cure for the oil smears and streaks on the landing gear and belly of his or her airplane. The routing and exit of the oil breather line cause most of these streaks and smears. Even if the oil loss is small, a tiny amount of oil makes a big mess of the belly when combined with airport dust and dirt.

Talk with a half-dozen A&P/IAs, and you'll get a half-dozen different recommendations for how to correct the problem. Continental had done a breather oil loss "cure" on the 0-200s, but it wasn’t explained and no part number was listed anywhere.

After doing some serious digging among the various Continental parts and service manuals, the Continental recommended "cure" can be found in the O-200 service manual.

The Continental assembly (the two pieces joined) number is 633182, but it is almost impossible to find in the parts catalog. It is made up of the usual AN 842-10 fitting and the new tube. The new tube’s part number is 633250, but it isn't in the parts catalog. Have one made and sanctioned by your IA instead of buying it from Continental because the price seems to be outrageous. In the 2000 catalog it was listed at nearly $240!

The two sketches tell the story. The added tube is copper, brass, or steel with the outside diameter machined to fit inside the bored-out portion of the AN 842-10. The difference in outside diameter of the pipe and the inside diameter of the fitting should match the process used to join them—about five-thousandths for brazing. Brazing is stated to be compatible with the other materials of the engine.

[Right] The "normal" installation, as built, showing how the breather fitting is pointed vertically downward form the crankcase.

[Right] Comparing the stock breather tube to the modified breather tube. The modified version has an approximate 2-¾ inch extension that is inserted into the breather tube cavity on the crankcase.




[Right] This view of the right half of the crankcase shows the modified breather fitting installed. The extended breather tube is still recessed within the cavity and does not interfere with any component engine parts.

[Left] Continental's cure was to modify the brass right-angle breather tube fitting (Part No. AN 842-10) that screws into the top right-hand corner of the engine and attaches to the hose leading to the breather tube. The modification attaches a tube to the end of the fitting, which goes into the engine. The purpose of displacing the pickup opening of the fitting is to "hide" the opening from the droplets of oil flung by the cam and the front bearing.

On the left, a stylized view of the oil droplets flung toward the opening of the breather's AN fitting. Some of the droplets are captured in the fitting and are blown out the breather and onto the belly. On the right, the extension is shown and indicates how its opening is not subjected to the ingestion of the droplets of oil.