Comanche 180 - wandering RPMs & roughness

[Ray B]

Quint we had a 180 Cherokee with you rough running symptoms years ago and after many unsuccessful remedies we drained the carb and found water and crud. Once drained she run smooth again. Not all shops drain the carb at annual. Might be worth checking, it's cheap to check! Ray B

[Quint Van Deman]

[Quint Van Deman]

[skipsouthernsky]

Dear Quint,

When at the Lycoming Engine School course, this subject was brought up. (The drain is generally a 1/8 inch pipe plug that is safety wired after tightening). They recommended that during a 100 hour inspection, this plug be removed and all the fuel drained out of the carburetor bowl and that before reinstalling the plug, go inside the plane and turn on the fuel and the electric fuel pump for 15 seconds or so. (no smoking!) The reason for that is so that fuel will go inside the empty carb bowl and swish around, picking up any residue or debris that might just be lying on the bottom of the bowl and carry that out at the drain point. After that go ahead and tighten the plug and safety wire.

This is but one item on a 100 hour check list.

Sincerely,
Skip Dykema

[Ray B]

Caution! Do not over tighten the carb bowl drain plug. It has a tapered pipe thread and thus can be over tightened to the point of cracking the carb bowl. Don't ask me how I know. Ray

[Quint Van Deman]

All--

So another flight in the books, and it turns out that I wasn't entirely crazy. The prop did overspeed, it just didn't do it during the flight phase that I expected. Since starting this thread I'd been watching the tach like a hawk during high power settings, but hadn't noticed anything of note. As it turns out, when I did see the overspeed, it was at the exact opposite end of the spectrum, during a descent at about 120 mph IAS and 15" MP. Does this lend any further clues to this saga of mine? I broke out the log books and the last time the prop governor was adjusted might have been 10 years ago. So I'm taking the 180 into the shop to have a 100 hr check done (including draining the carb & using the checklist on the site) and do a prop governor adjustment/overhaul. Thanks all for the help & I'll post the results of the work for the sake of others.

-Quint

[MULEFLY]

As a very quick and cheap data point on your prop speed... taxi it out at night and if you have non-incadecent lights on the field (hanger and night lights)... advance your props to 2400 rpm... and see if the 60hrz strobe effect from the lights verifies the 2,400 rpm...
Jim

[Quint Van Deman]

I might do that just for the fun of it

The 180 went into the shop today with a solid list for the mechanic based on all of the feedback I've gotten from you all.
I will post the results shortly.

Thanks again.

-Quint

[Quint Van Deman]

Well the news in the last 24 hours has gone from bad to worse:
The first report was that there was metal in the oil filter, which seemed to correlate all of the various symptoms. The hypothesis was that it was a piston pin and a *relatively* easy fix. The second report was that all of the cylinders came off and all looked good, but that the cam shaft that was installed during the last overhaul was an undocumented narrow lobe cam that has a 1200 TBO (engine is at roughly 1300). That in combination with the unknown metal source coming from within the engine is making it sound like overhaul time.

Does anyone have any thoughts about this sad twist to my tale? The frustrating part is that I had a combination annual/pre-buy done to help me reduce the risk of this very occurrence, but that in retrospect those inspections were sabotaged by the previous owner changing the oil 3 hours ahead of time & having a poorly documented overhaul entry, neither of which I knew to ask about. Live and learn I suppose, but this one is a hard pill to swallow having only owned the Comanche for 50 hrs.

Frustrated & not liking my options,

-Quint

[N3322G]

Quint, sorry to hear the tale of woe.

I used Comanche owner Charlie Melot's shop Zephyr engines in FL, highly rated by Aviation Consumer, and have been happy with the Twin's overhauls.

[Jay]

Bum deal. But on the bright side, you'll be able to get a solid overhaul done now, no more mystery parts. And you found the problem before anything REALLY bad happened, that's a good thing!

Jay

[Quint Van Deman]

Yep, I'm all for finding problems on the ground. I just prefer the ones that don't cost 20k!