Continental 0-300 problem

[B Hunt]

Has anyone experienced a problem with the rubber push rod housing seal coming off the push rod housing. It has happened several times on my 0-300. I have replaced the rubber and clamp, but it still comes off. Any thoughts?

[Speedbird48]

This probably not the correct form of this type of question, but here goes.

The Cessna Pilots Association has a very good Technical Support organization so as a Cessna owner you might consider joining them. If you can't find them send me a PM.

For my part of this and an A&P/IA I would think that you have some pressure in the pushrod tube that is pushing the seal off. Or, the tube and the seal are worn out. What is the compression on that cylinder?? When you check it take the rocker cover off, and listen for leaks.

Speedbird48.

[B Hunt]

Thank you for the reply,
I have replaced the rubber and clamp .
The compression is 74 for this cylinder.
How would pressure get into push rod tube?
The crankcase vent is open?

[Tree]

There is a raised (dimpled outwards) ring around the cover tube to prevent the rubber seal from migrating outwards. If the outer clamp is not positioned on the crankcase side of this ring it will migrate. Try warming the rubber with a hair dryer, loosen both ring clamps and push the rubber very hard towards the crankcase then reapply the clamps. Also the cover tube may be crimped in this area or the raised ring may be worn down or manufactured too small.
Unfortunately you must remove the cylinder to replace the tube if it is defective.

[B Hunt]

Thank you for your help it is much appreciated

[Brian Abraham]

Have a look at Real Gaskets Corporation - Gaskets for Aviation, Automotive and Motorcycles (http://www.realgaskets.com) One advertising spiel by a retailer has this to say of the product "an improved silicone gasket manufactured by Real Gasket Corp. These push rod seal kits are made from silicone rubber for long life and improved temperature and chemical resistance. This is especially helpful on the Cessna 337 where heat destroys traditional rubber push rod seals. Many existing push rod housings have nicks and roughness from the previous seal washer that causes seals to leak. The new seal moves the seal washer to a different location away from any existing nicks or roughness. The new seals are taller and have a crown washer that increases the spring compression resulting in increased seal pressure. By adding a taper to the seal, the crown washer pushes inward against the push rod, helping it to seal. Finally, you have 37% for sealing area with the new seals."

Have a looksee here also REAL Lifetime Silicone Gaskets (http://www.magnalabs.com/realgasketfacts.htm)

I have no experience or association with the product or companies.

[SNS3Guppy]

I wouldn't count on pressure pushing the seal off. Generally when a seal migrates, it's improper clamping.

When you do a compression test, remember that the compression value you get isn't particularly important, and doesn't tell you much...but what you hear while you're doing the test tells you a lot. The compression test does record a value, but it goes up and down with the cylinder temperature, test set, person performing the test, way in which the test is performed, etc. What the compression test doesn't record is the sound you hear of air escaping the induction (intake valve leakage), through the oil cap (crankcase/ring leak), or through the exhaust (exhaust valve leak).

Make sure you have a clean surface underneath the pushrod seal. Some like to lubricate the seal and the pushrod surface with oil, or other lubricant. In this case, the seal may migrate anyway, and excess pressure to prevent it can damage the pushrod tube itself. Keep it dry under the seal, use moderate clamping pressure, and where more than one clamp is used, have the screwpoints on opposite sides of the tube.

It's not uncommon to find the pushrod housing out of round due to previous overclamping. If this is the case, you'll never get a good seal except by accident, and you can expect the seal to migrate. Check the housing (pushrod tube) thoroughly before reinstalling.