Prop Problem?

I've got a problem which has stumped a lot of very talented, experienced, bright folks, and was wondering if anyone has run into a similar problem over the years.

Background: Two unknown quantities: Different rear engine (low time), overhauled rear prop and governor. Everything worked fine on old engine, prop, and governor.

Now: I'll fly for 1 hour, get it hot, land, let it sit for half hour . . . start it up, and after about 10 minutes on the ground, the rear prop goes, and stays in feather position.

It originally happened to me a few of weeks ago on a LA mission, and I was stranded. Let it cool long enough (overnight), and I can start the engine, take out of feather, and fly away. But . . . after I fly for an hour and let it sit for a half hour or so on ground, it repeats itself. No problem at all when I land and taxi, no feather or loss of RPM issues. But, let it sit for half hour, and it feathers after about 10 minutes.

It's never feathered on me in flight . . . yet.

No, I'm not still flying it . . . I've just tried the following.

Had governor checked by prop shop, and returned to service and yellow tagged -- I tried to fly it and the same thing happened.
They swear it ain't the governor!

Called Continental because the prop shop swore it was a defective area around the main bearing transfer area.
Continental sent me a Technical Brief to check for oil pressure. IA performed test per Technical Brief. Minimum pressure differential was supposed to be 12/80. Test resulted in 27/80. Passed with flying colors. (Continental thinks its a prop problem).

Prop shop took propellor back, changed out more parts, and sent it back returned to service, yellow tagged and re-sealed.

Flew today, and same thing happened.

So . . . what say all of you experienced Skymaster folks? I'm stumped, IA is stumped (still thinks it's a prop problem), and clearly, the prop shop is stumped.

I'm checking with other prop shops, but am wondering if the same scenario has happened to anyone else in the history of Skymaster kind.

Thanks,

Keven
________
Buy cheap volcano vaporizer

[KyleTownsend]

I encountered this same problem earlier in the summer. It turned out that I had a "compound" problem. First, there was a piece of trash under the oil pressure relief valve seat. This was evidenced by lower than normal oil pressure when the oil was hot and less viscous. Second, I had a partially blown seal in the prop governor. It took about a week to narrow everything down and get it fixed.

We thought we had the problem fixed several times. However, it was very hot and I was at Dallas Addison (read lots of ground running before you get to take off). Typically, about the time I would become #1 for takeoff, the prop. would feather. ARGH!

In my case, there was insufficient pressure in the hub to hold the prop out of feather at RPM's just above the point where the mechanical locks engage to prevent feathering (idling at around 1,000-1,200 RPM) when the oil was good and hot.

When we were discussing possibilities, I recall that the main bearing seal on the crankcase was mentioned as a possible culprit. I think this is what you checked for with the test that Continental had you do (I assume that the oil was plenty hot when you did the test???).

I also recall hearing that this was a somewhat common problem on the Piper Senecas which also have the IO360's.

Continental, and several others, recommended using a fairly heavy straight weight oil if everything else failed. You might consider this.


Good Luck!

Kyle

PS: My rear engine was recently overhauled as well. It was a piece of overhaul debris that was causing the relief valve problem. I also noticed that this valve sure didn't get overhauled as part of my overhaul. We ended up replacing several springs, etc. because of its poor condition. However, my main problem was the seal in the governor (it was an O-ring that was missing a little pie shaped wedge out of one side). I thought I would never get out of Dallas!

[kevin]

Continental replaced my factory reman with exactly the same symptoms. Clue was, watch the oil pressure as the engine gets hotter and hotter. It drops close to the minimum line on the Cessna guage (but not below) and prop feathers. It took writing a letter to the president of Continental (with a copy to "the executor of my estate") to get the replacement done. Continental tore down the engine and found everything nominally within spec, but all the bearings etc were on the low side of spec, and the additive effect was to make the engine "too loose" when hot. (That last is a quote from the Continental teardown tech.) Continental replaced my engine under warranty.

Kevin