The Cessna 120-140 Association Forum

What is the proper path for routing the engine breather tube? Mine currently goes inboard of the filler neck for the oil tank and then goes down to a bracket next to the gascolator. My mechanic and I are thinking that isn't right...

-- Chris B.

You and your technician are thinking correctly. That routing is not correct.

As I recall the breather tube should end up close to the outboard co-pilot side corner of the bottom cowling opening.

So outboard and/or below the filler neck.

Does anyone have photos of how their breather tube is routed? If you can include shots of the brackets and where they attach, it would be greatly appreciated. Thanks.

When these planes were certified it was common practice to run the vent line straight down and aft from the fitting. This tends to encourage oil vapors to make their way out the tube along with the blow-by. Over the years many have been rerouted along the top of the engine then down along the firewall. I'm attaching a service bulletin that shows the modification on Ercoupes. My (Cessna) has a double adel clamp on the engine mount and a standoff on the firewall with a single adel near where it exits below the firewall. Be sure to drill a hole in the tube six inches or so above the bottom of the firewall to allow breathing in case the end of the tube freezes up.

The tubing comes in two pieces and there are two 3" pieces of rubber hose with clamps connecting one tube to the fitting on the engine and the first tube to the second. The second tube has a single bend where it exits the cowl and the joint is about even with the cylinders. An MS35489-17 grommet is used where the tube passes through the rear baffle.

Here is a picture of the breather tube "over the top" on a 120, if you choose to go this route.

At the very least, your breather tube on the 'stock install' goes outboard of the oil tank. You're almost a good 4 inches too high in placement.

The above picture has the breather tube "insulated" with standard fuel/oil line aviation "fire sleeve". Considering that if you fly in cold temps, then you need to realize some water vapor exits the engine and could freeze in the very cold air above the cylinders during winter ops.

If the breather line is below the cylinders (as yours currently is) or behind the baffle, then the air is much warmer and no need to insulate.

Take a look at your last picture. Envision the tube, not routed by the filler neck, but about mid span to the outboard side of the oil tank, aimed directly at the engine mount brace that is visible in the background. (mounting to the lower copilot side of the firewall) Adel clamp the breather tube to that engine mount tube and you'll have a "stock install".

Where did that engine come from? I worked for a shop a "few" years back that wanted to compete with the "Victor Black Max" engines and chose Ford blue... (Didn't last long, thank goodness!)

It's a "Victor Blue Max" special..........I paid a lot of money for that engine.

(Rob: We need better Smilies!)

Here's my 0-200 set up, right or wrong been that way for 25+ years...