Grease or Oil on Back of Prop Blades - Now with Pics!

They pulled the Arrow in yesterday and took a look. Verdict - engine oil, most likely from the crankshaft seal. Nothing found wrong with the prop or hub. The A/P at our shop called the shop that OH'ed the prop and governor in May. They both agreed that the prop could be serviced (greased) and sent on its way. A/P also recommended doing the crankshaft seal replacement at Annual (which is in mid-March) and that we are cleared to fly. He just mentioned keeping an eye on oil levels which we do before startup each time anyway.

So, all-in-all... a pretty good report. Thanks for all the suggestions and also for letting me type these posts as I waited for news instead of biting off my fingernails out of sheer stress and worry. All great suggestions and comments... but @guzziguy is winner-winner-chicken-dinner this time. Lol.
 
When we had the shaft seal problem, we wiped the front end of the engine clean during the preflight, every time, and for shorter flights, oil on the prop ceased to be a problem. We kept a can of de greaser and a box of heavy shop wipes in the plane for this use.

Very happy that your oil came from the shaft seal too. Putting it off to the annual is a good choice, that is what we did.
 
In industry its called "tramp oil". It can minutely ooze thru anything and will go everywhere.
 
Deelee said:
Something else - When I flew on Saturday, it was probably the coldest weather this aircraft has flown in. Does cold weather affect the seals somehow where they would contract enough to let a little grease out and cause this?
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If I recall correctly, the Challenger was brought down by an o ring seal that failed due to cold weather.

If I don't recall correctly, I'm sure someone here will correct me and explain why I am wrong.

edit: I now see that you have likely identified the cause.
 
There's also the O-ring in the prop hub that seals to the crankshaft nose. It has around 300 PSI oil pressure on it, from the governor. Obviously, it doesn't take much nicking or foreign grit to let that thing leak. Or a scratch in the hub's O-ring groove left by the last guy that took the ring out with a steel pick.

I once took a prop off and found that O-ring not in its hub groove, but slid over the crank nose and the prop installed over it. There's a chamfer around the hub's hole that kept the O-ring in place in spite of it being installed totally wrong. The fact that it wasn't leaking a lot amazed me.

Overgreasing a hub happens, too. You can shove residual air out, leaving no place for grease to go except past the seals when temperatures go up and the grease expands. Follow the manual. There's no need to purge old grease. There's no combustion going on in there, no moisture getting in unless the prop is shot anyway. In fact, the Harzell manual will tell you that it's not possible to purge old grease through the lubrication fittings. That requires hub disassembly and cleaning.

The manual for Hartzell Compact hub props: https://hartzellprop.com/MANUALS/115N-0000-A.pdf

Go to Section 6 for cleaning and lubrication instructions. Note the stuff on pages 6-10 thru 6-12. One ounce of grease, maximum, or until it appears at the other fitting hole, whichever happens first. No more than that.
 
Deelee said:
They pulled the Arrow in yesterday and took a look. Verdict - engine oil, most likely from the crankshaft seal. Nothing found wrong with the prop or hub. The A/P at our shop called the shop that OH'ed the prop and governor in May. They both agreed that the prop could be serviced (greased) and sent on its way. A/P also recommended doing the crankshaft seal replacement at Annual (which is in mid-March) and that we are cleared to fly. He just mentioned keeping an eye on oil levels which we do before startup each time anyway.

So, all-in-all... a pretty good report. Thanks for all the suggestions and also for letting me type these posts as I waited for news instead of biting off my fingernails out of sheer stress and worry. All great suggestions and comments... but @guzziguy is winner-winner-chicken-dinner this time. Lol.
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Glad it worked out.
I accept bitcoin
 
Dan Thomas said:
I once took a prop off and found that O-ring not in its hub groove, but slid over the crank nose and the prop installed over it. There's a chamfer around the hub's hole that kept the O-ring in place in spite of it being installed totally wrong. The fact that it wasn't leaking a lot amazed me.
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That is the correct location for the o-ring in some applications. Because of that I'm not terribly surprised that it sealed up well enough to work. I can't help but wonder if whomever put that prop on was thinking of the other style hub and not paying attention.
 
mondtster said:
I can't help but wonder if whomever put that prop on was thinking of the other style hub and not paying attention.
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Probably. The O-ring groove in the hub was empty. It was on a 185, and the manuals clearly show the O-ring in the groove.
 
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