185 propeller issue

i was flying home from the cabin last night and was about 15 minutes out from home base when the prop started surging from 2400rpm to 2500 and back. after a minute or two of that it settled back down to 2400 and so i continued on. just when i got over the middle of knik arm(of course) a vibration set in, probably not that marked but since the tide was out and i was over mudflats it seemed worse. by taking the power down to 22 squared the vibration went away and i flew the remaining 2 minutes back to fire lake with a little more pucker factor than i like. after landing when i pulled the power the rpms went down to 300 RPM which is lower than normal. the prop/engine also didnt sound "right", had a very tinny sound. i have a 6cyl egt/cht gauge and throughout all this the egt and cht's didnt move. i also have an ei fuel flow gauge and when the prop was surging the fuel flow went up and down as you would expect. the cessna oil temp and pressure gauges also were in their normal position and didnt change. after tying up to the dock i didnt see any oil leaks immediately visible on the prop and the engine oil level was unchanged. i have a call in to my mechanic this AM but thought i would throw this out there to see if this rings a bell for anyone. i am assuming the problem is in the prop but if i have learned anything from owning planes it is that the problem is usually the most expensive possibility. on the bright side the silver fishing on lake creek is great right now, my wife and i limited out fri,sat and sun and we didnt even get out there until 7pm friday.

Is your prop due for an overhaul? The prop on our 180J is due for an overhaul. When I asked what happens if we don't overhaul it right now I was told that sooner or later the prop won't hold a power setting and the RPMs will start to fluctuate. Sounds like exactly what I've been waiting to see in our 180. I'm no expert but I was just talking about this same thing recently with the mech.

You have either a Prop, Governor, or Oil Passage issue.

Low oil pressure will cause an uncontrolled increase in RPM on a McCauley. What brand is your prop?

Also, a clogged screen at the base of the governor might limit the amount of oil available to pressurize the prop. Clogged could signify your motor making lots of metal.

Don't know what airplane you have, but I would not treat this event lightly. IO-520's have quit from broken cranks.

Let us know what comes of this, please. DAVE

How much time on your engine since overhaul??

I second checking the screen on the governor gasket.

Also could be a bad governor.

Also there is a collar that goes around the crankshaft that supplies the oil for the governor/prop.
It has a really close tolerance. It could be worn and not allowing pressure to build to control the prop.

Usually if this is the case it will work normally when the oil is cold, but change as the oil reaches operating temperature.

when doing your run-up and cycling the prop, look for a large drop in oil pressure when you pull the prop knob back. this could indicate a clogged oil suction screen.

as stated earlier, pull the governor off and check the screen in the gov gasket. if it does not have a screen- replace it with one that does.

and the most likely culprit- the prop governor. they get sticky. infrequent use and/or old age can lead to rusted pilot shafts which causes "hunting".
borrow one from a friend and try it, if possible, before sending yours out for o/h. it can take a couple weeks.

Alwasys Pull engine oil screen and make sure clean first.... A cracking crankshaft will cause similar fun.... Somewhere here I told my story of one.....

Will look for thread...

http://www.supercub.org/phpbb2/viewtopic.php?t=21510&highlight=prop+governor

just got off the phone from my mechanic and my standard theory of aviation economics holds true. the problem wasnt the prop, it is the most expensive possibility, a broken crankshaft. that really put a pit in my stomach, assuming it broke when the surging started i flew for about 10 minutes with a broken crankshaft. most of the flight was over areas with plenty of landing areas for a float plane but if the engine had seized at an inopportune time i might have been putting it down on the mudflats off birchwood or on the football field at chugiak high. i'm really surprised at how smooth it ran for most of the time, either a broken crankshaft isnt as horrendous as it sounds or i was very, very lucky. at any rate my threshold for precautionary landings just got really tiny. the engine was only about 900smoh but the overhaul was over ten years ago, the plane sat for a long time before i bought it five years ago. now i get to go shopping for an IO-550 about 5-10 years earlier than i thought i would.

It doesn't crack all the way though at first but does a spiraling crack from where the transfer collar rides on crank shaft( no bearing, steel on steel real tight tolerance area)

So your engine will run fin but will dump oil that should have went to prop back into crankcase


So they did find metal in screen? or?

so... now that you are breaking in the new engine...

in the other thread http://www.supercub.org/forum/showthread.php?39402-new-engine-break-in-procedure

did you get post mortem pictures of the broken crank and such to share???

i admit it didnt occur to me to take a picture. the engine has long since gone off to alabama or wherever cores go to die. FWIW my mechanic told me to go ahead and get the factory new instead of a reman because he said it was less likely they would reduce the credit for a core with a broken crankshaft if i was paying top dollar. if i had gotten a reman and they reduced the credit the overall cost to me would be about the same. as it turns out i got full credit for the core whether this has anything to do with it or not.
on the flight where the crank went out i landed at fire lake in eagle river. from there i had to try and figure out how to get it out of there. my mechanic happened to be taking an identical IO-520 off a commercially operated plane at the same time. it had gone to TBO but was still running fine. we pulled the plane onto the shore at the lake and he swapped engines. i actually only had a couple weeks of downtime. after float season the upgrade was then able to be done right in a hangar rather than outdoors on the shore of a lake.

I liked the way Dave and Mike called it out beforehand.