What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Strange discoloration on flywheel after prop removal

Sleepy

Member
Sponsor
I removed my prop the other day to take it up to Northwest Propeller for some edge work. After I got back to the hangar, I decided to take off the flywheel and change the alternator belt. To my surprise, I discovered the two mating surfaces between the flywheel and the crank where stained (see below). The mating surfaces on the other side between the flywheel and prop are clean.

This is off an RV-4 (1992) with about 850 hours on the engine and 300 SOH (2008) on the prop.

While the stains look oily they are not. There is very little build up and they are dry. Any ideas about what is going on?

Thanks,
Scott


 
Bolt torque?

Have the prop bolts been torqued properly with every seasonal change? It looks like they have been loose at one time or even for some time. A wood prop that is not properly and regularly torqued can even catch fire from the friction of movement on the flange.

Vic
 
Last edited:
Have the prop bolts been torqued properly with every seasonal change? It looks like they have been loose at one time or even for some time. A wood prop that is not properly and regularly torqued can even catch fire from the friction of movement on the flange.

Vic

Didn't the poster indicate the discoloration was between the crank and flywheel? (Not the prop and flywheel.)

Maybe there is a loose fit between the crank lugs and flywheel? In any case, it does look like a heat related event with slippage between the two surfaces. I'd check the fit and also take a close look at the prop and the bolts.
 
Are those oil stains on the inner bore of the flywheel? Maybe the crank seal leaked at some point in the past? Not sure how that would happen but the flywheel looks oily....
 
Paint

Could someone have painted the back of the flywheel where it was not meant to be painted?
 
In your first picture it looks like the wood prop has radial stains on it in the area of the lightening holes. Sure looks to me like some liquid/grease spun out from the hub area.
 
It looks like oil contamination to me but hard to tell.
Clean flange and flywheel, check for pitting, marring, scuffing etc... If something is moving, there should be wear marks.
Check tolerances of bolt holes for flange, flywheel, and prop, have bolts inspected (any prop shop can do this), install reworked prop, then set up an inspection interval. I would inspect at 5 hours, 15 hours, and 50 hours. Those are pretty arbitrary numbers that i would discuss with my AP friends and other resources
 
Wood prop or metal? And what is the streaked material and black material visible through the holes in the first photo? The streaked material seems to be completely filling the big lightening holes
 
Wood prop or metal? And what is the streaked material and black material visible through the holes in the first photo? The streaked material seems to be completely filling the big lightening holes

Those are not holes they are in the other part not shown in that picture but does show what was going on. Look at the streaks show in that photo and the center hole clearly oil stains.
 
Thanks everyone for your comments. Here some answers to the your questions. As for cleaning and further inspection that will have to wait until I get back from my work trip on Thursday evening.

1. The propeller is a extended hub constant speed Hartzell and was installed new on the RV-4 in 1992.

2. The engine is a Lycoming IO-360-B1E which was originally installed new on a Hiperbibe. It was removed at about a 150 hours, torn down, inspected, rebuilt and subsequently installed on this RV-4 several years later. I am assuming there was an accident with the Hiperbibe, but there is nothing in the logbook stating why the engine was removed.

2. The propeller has not been off the airplane since I bought the aircraft in 2012. According to the logbook, the last time it was removed was for an overhaul and installation of a new AD compliant hub which was in 2008.

3. According to the logbook, the bolts where torqued to 75ft/lbs during the last install. I suspect this is probably accurate as they were a real a bugger to get off last week.

4. The material in the flange of the flywheel is a thick wet grease like material. I assuming oil. The aircraft has always had a small amount of oil resting on the bottom seam of the case just aft of the boss mount for the alternator. Nothing major, just a few drops, but always there. There was no oil on the back of the flywheel or the back of the flange on the crank. My guess is the propeller was leaking a the seal at sometime in the past and the drops of oil are unrelated, but I will need to do some further examination.

I will clean it up and repost some more pictures when I get home tomorrow.

Thanks again for the help.

Scott.
 
Looks like oil staining to me. Hard to imagine fretting between the flange and flywheel to be limited like this.

Larry
 
Back
Top