The Cessna 120-140 Association Forum

Good morning all.
During my walk-around pre-flight yesterday, I happened to jerk my prop to test my brakes and the prop
had a definite wiggle. I don't recall this wiggle ever been present before. I have a CONTINENTAL C-85-12F with a
69.5X69 prop. I have found nothing on-line that gives me a good explanation to this situation. I flew a good 2 hours the
previous day and I was impressed with the way my little jewel ran and sounded.
Before I fly again, I would like to get some info on this little wiggle that has suddenly appeared.
Tapered shaft....all prop bolts were tight and wire-tied, just the wiggle.
I would appreciate any info.
Larry Surratt
1946 C140
89011 ( very early) Complete rebuild in 1993

Are you referring to crankshaft end play? In the longitudinal axis/thrust bearing? I think that would be the only slop that should be felt by hand for the crankshaft. I am pretty sure there should be no radial play detectable on the main bearings. Those tolerances would be on the order of a few thousands of an inch.

Surely if the prop is moving on the crank that is bad news.

Maybe that was a typo but I would expect it to be the flange style crank if it is a C85-12F. Do you have the tapered crankshaft with a nut that secures the prop to the crank?

A better description of your "wiggle" will allow us to help you decide is this is serious. "End play" as described above is normal and is typically associated with a "tunk", or "Thunk" sound inside the engine. As in as you are pushing the airplane by the prop or pulling the airplane by the prop, fore and aft. All Aircraft engines (air cooled) have this. it's normal.

If on the other hand you are rotating the prop and it seems to "wiggle" in relation to the crank that could be extremely bad. Purhaps a diagram, photo, or better explanation and we can help you out.

Fore/aft limits

Crankshaft to Thrust Washers Service limits .025

Here's how I measured mine when I had a concern

If you have a tapered shaft then you have a C85-12. The "F" distinguishes the Flanged shaft.

I'd take the prop and hub off and inspect the taper and the hub very closely. A loose prop nut will allow the prop to wobble on the taper. I've seen cracks in the taper that also allowed the nut to loosen, which probably made the crack propagate...

I don't suppose you are leaking oil from the front of the engine, too, are you?

The last thing you want is for the prop to fly away on its own.

Back to the 'prop wiggle'....I pulled the prop to inspect the hub. Now is there an easy way to get the
snap ring back on? Maybe I'm not strong enough anymore or I don't have the correct tool.
I appreciate any information.
Thanks.

Larry Surratt
C-85 12-F
89011

You mean the snap ring that holds the nut in the hub? Don't know; never removed one. Brute strength jumps to mind...

PM me your email address and I'll send you some R&R info for the hub.

Also, check the taper on the crank carefully for cracking, especially around and under the Woodruff key.

Larry Surratt
Are you saying the snap-ring came out of the tapered hub?
If so, just expand the snap ring to a larger dia. and install it
back into its nesting place!

The same thing happened to me once and by expanding
it did the job!

Also, you should have left the prop on the prop hub
and the snap ring in place to be able to remove the Prop Hub from the Crankshaft!

The prop hub is also designed to be a self-contained puller for removal from the crankshaft

First , remove both carter pin and clevis pin that holds the front nut onto the prop hub
as the big front nut is threaded onto the front of the crankshaft.

Second, get a 2-to-2 1/2-foot by 5/8 in. DIA. solid bar that will fit into the big hole on the front nut.

Third, with the prop on the prop hub adapter and the snap ring in its place, hold the prop and unscrew
the front nut with the 2-to-2 1/2-foot solid bar!

If it doesn't break loose, apply some dry heat to the front of the hub adapter with a Heat gun!
Also, if the snap-ring pops out, just spread it open a bit and reinsert it with the end of a flat blade screwdriver beginning at one end of the snap-ring first!