On a trip over the 4th of July I came to the thought that my right prop governor may need to be overhauled. When I set prop RPM in flight (e.g. 2400rpm) the left engine stays steady and the right engine rpm bounces a bit. The net effect is it is difficult to keep the props harmonically in sync. The right will sit at 24 and then drop a little low (to say 2350rpm if I can believe the gauge) and then bounce back up (to say 2450) before hovering back around 2400. The prop sound goes in and out of sync which is a bit annoying on XC.

Anyone have any thoughts on this and anyone have any guesstimates on the cost of an IO-320 prop governor overhaul cost?

Thanks,

- Charles

Charles,

First, check the pressure in the prop dome and service with Nitrogen if needed. If not in spec, test fly again. It might be worth checking the line from the governor to the front of the engine to make sure that it does not have a sludge build up.

Assuming that a prop overhaul is necessary, I recommend Southwest Aero in Washington state (206-575-8732). I had both of my done in 2010. The flat rate for the overhaul was $400. One governor came in that the flat rate. The other needed parts, so was a bit more. Even if you are only going to overhaul one, I would send both and ask them to set them up identically so that you don't end up with split prop controls in flight. If they haven't been overhauled in a long time, I would have them do both and of course set them up the same.

Thanks Kristen that is great info. Greatly appreciated...

- Charles

Charles,
The prop is "dumb." It's only going to respond to oil pressure. What you're describing is a common symptom of an internal leak in the governor.

I've learned recently how temperamental our PA-30s are to internal governor leaks. The combination of the feathering spring and nitrogen charge in the prop creates more resistance against the governor than any other light twin using the Hartzel F-6-3A. Relatively small leaks in the governor can cause prop surge.

If you need a prop governor overhaul, I highly recommend Palm Beach Propellers Inc. Tell them you have a PA-30 and they'll ensure your new governor meets tighter leak rate specs. The overhaul facility is permitted to allow an internal leak rate of 15 qt/hr after overhaul. Many have found the PA-30 props can start surging with leak rates around 15 qt/hr, so PBP will ensure your PA-30 governor has a leak rate within 10 qt/hr at the time of overhaul. I'm not affiliated at all, just love working with them.

When reinstalling the governor, I suggest using the cheaper Lycoming gasket between the governor and the governor drive extension. The thick gaskets with filter screens tend to cause leaks on our PA-30s due to high pressure and inability of the thick gaskets to compress enough. I pulled my governors (both engines) multiple times for leaks until Zepherhills engines tipped me off to the gasket compression. Anyone will have the standard Lycoming gaskets, but be sure to specify that's what you want else they'll send you the thicker one.

David, WOW this is great advice and intel thank you. On my last couple flights the engines seemed to stay in sync and a friend flying with me thought the culprit of my slightly oscilating right tach might be the instrument itself - entirely possible. I'm going to keep an eye on it but in 6months at the next annual I may just send the prop governors out for OH to be sure. Thanks for the shop reference and the PA-30 details.

- Charles

Charles,
It should be pretty noticeable. You'll be able to feel the plane yaw (in calm conditions) if its surging on you. Good luck!

 

As Kristin noted Southwest Airmotive in Seattle is a great shop for prop governor work. ( But I always wonder why "SouthWest Airmotive" is in the Northwest !) They have done all my work for years, and I find their work and prices to be excellent.

Al Powers ICS 2978

Al - great to know thanks! Sounds like there are several good options.

Many Thanks,

- Charles