hydraulic lock

[egp8111]

I've owned four 912 powered airplanes over the years(2 KFs) and all would lock up if left sitting for a period of time usually a couple of weeks or longer. It is almost always caused by oil in the #4 cylinder. (pull the bottom #4 plug and about a tablespoon or so of oil runs out and your good to go) My latest KF IV seems to be much more prone to doing it than any of my previous airplanes in a shorter period of time . Any ideas on what could be the difference (oil tank height?)or possible solutions. I'm getting pretty quick at dropping the cowl and pulling the plug but its kind of a PITA when you want tot go fly.
Thanks
Skip
NC

[Shadowrider]

Have you tried burping it after flying? I wonder if that would help to try and return the oil back to oil tank. Is your oil tank higher than the engine? Are you running rotax oil filter with check valve?

[Dave S]

What Dustin & shadowrider said....

You didn't mention what kitfox model/series you have, however it is my understanding that the earlier craft
had the oil tank mounted quite high possibly allowing drainback.

FWIW our S7 has the lower tank mounting.

I have gotten accustomed to always burping the engine after a run (hot oil burps quicker than cold) and have never had a problen with hydraulic lock.

[egp8111]

It's a KF IV.(round cowl) I'm using the Rotax filter. I've always burped it before flying not afterwards, should I do a post flight burp as well? I'm just curious why this engine seems so much more prone to locking up than my previous 912s.
thanks
Skip

[Slyfox]

Have you tried burping it after flying? I wonder if that would help to try and return the oil back to oil tank. Is your oil tank higher than the engine? Are you running rotax oil filter with check valve?

let me say first off that I have over 3000 hrs in the kitfox alone. I'm on my second motor. Burp the engine after a flight, really? I always check my oil level after flight, why?, because the level is at the top of the stick at that time. I don't understand your reasoning on burping the engine. In fact out of 20 years of flying my kitfox I never burp the engine before flight. Why? Because I fly every day and the oil level has proven to be with in range and I always turn the engine over 8 blades. Never had a problem. Yes one time I let the engine sit a few weeks and yes one of the cylinders filled with oil, I removed plug and got the oil out. Now with all this said, I have an oil thermostat mounted to the top of the gear box, I believe that has slowed the oil from draining out of the tank. take care

[Slyfox]

It's a KF IV.(round cowl) I'm using the Rotax filter. I've always burped it before flying not afterwards, should I do a post flight burp as well? I'm just curious why this engine seems so much more prone to locking up than my previous 912s.
thanks
Skip

I feel if you want to reduce the problem, maybe put the tail on a saw horse to keep the aircraft level.

[Av8r3400]

I've been flying Kitfox 4s with 912 engines for 14 years, all with the "improper" oil tank placement of the OEM engine mount.

I have NEVER had a oil-hydrolock.

I have NEVER done a post flight engine-burp.

I ALWAYS pull the engine through at least 5 full rotations before attempting to start and burp before the first start of the day.

I ALWAYS run the Rotax oil filter with a check valve in it. This is key to preventing oil syphoning and hydrolock.



There must be something in your oil line routing or some other source that is causing the syphoning to happen.