Corroded prop bolts

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Corroded prop bolts

Postby lutorm » Wed Oct 25, 2017 3:39 am

We took the prop off our Aerovee over the weekend and had a hell of a time getting the prop bolts out. They were all severely corroded and locked into both the bushings on the prop flange and into the holes in the prop itself. We had to wedge a 2x4 between the engine and the prop flange and pry the bolts out while turning them from the front, and then pound them out the last bit.

This is what they look like:
Image

The prop hub is darkened and slightly crushed. I don't know whether the discoloring is from heat or just the corrosion on the prop flange transferring into the urethane coat of the prop.
Image

The scary part is that when the bolts are stuck like this, torquing the nut to spec doesn't really mean anything since you're just tightening it against the hole in the flange and the actual tension on the bolt heads is completely uncontrolled.

Anyone ever seen anything like this or is this a special feature of planes parked outside in Hawaii?
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Re: Corroded prop bolts

Postby GordonTurner » Wed Oct 25, 2017 6:07 am

Very interesting, thanks for sharing.

How long were those bolts in place? Assume new unused AN hardware to start....

Best of luck, guess you'll need to put that maintenance on a regular schedule.

Gordon
Waiex 158 New York. N88YX reserved.
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Re: Corroded prop bolts

Postby lgsievila » Wed Oct 25, 2017 10:34 am

My guess would be as you questioned
a special feature of planes parked outside in Hawaii
. Salt and salty air can do awful things to steel. Even if you have a cover over you cockpit I assume your prop is always out in the weather. How long had it been since you had the prop off??
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Re: Corroded prop bolts

Postby lutorm » Wed Oct 25, 2017 1:30 pm

lgsievila wrote:Salt and salty air can do awful things to steel. Even if you have a cover over you cockpit I assume your prop is always out in the weather. How long had it been since you had the prop off??

I recently became a co-owner so I'm not positive. It may have been as long as 5 years since the prop was off, but the bolts were released and retorqued maybe 6 months ago and at that time they at least were not completely stuck. They were not taken out at that time so their condition as of then is unknown.

The aircraft has been parked outside for 5 years but most of that time was at least under cover. That's no longer available so now it's in the rain and on a tailwheel aircraft the Sonex spinner creates a perfect pool where water will sit and can seep into the bolt holes. Not an ideal situation. I guess we'll have to find some sort of prop/spinner cover.

I wonder if the "C" corrosion resistant AN bolts would be a better choice than the normal cadplated ones, as well.
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Re: Corroded prop bolts

Postby Rynoth » Wed Oct 25, 2017 3:05 pm

I wonder if this should make the prop hub bolt seasonal torque adjustment include a similar process as the landing gear leg bolts.... to turn the head of the bolt to ensure that the bolt itself is free. Then torque the nut?
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Re: Corroded prop bolts

Postby GordonTurner » Wed Oct 25, 2017 3:55 pm

Good idea Ryan.
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Re: Corroded prop bolts

Postby daleandee » Wed Oct 25, 2017 4:46 pm

Rynoth wrote:I wonder if this should make the prop hub bolt seasonal torque adjustment include a similar process as the landing gear leg bolts.... to turn the head of the bolt to ensure that the bolt itself is free. Then torque the nut?


Annual inspection is a great time to disassemble these parts to inspect for corrosion, cracks, fretting, & wear. In a harsh environment it would be wise to consider doing so more frequently. Glad this was caught early!

Dale Williams
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Re: Corroded prop bolts

Postby lutorm » Wed Oct 25, 2017 6:33 pm

Rynoth wrote:I wonder if this should make the prop hub bolt seasonal torque adjustment include a similar process as the landing gear leg bolts.... to turn the head of the bolt to ensure that the bolt itself is free. Then torque the nut?

Well this is Hawaii, we don't have seasons... ;-) But taking it off at least every annual and inspecting the bolts sounds like a good idea. I'm hopeful that if we can at least avoid standing water in the spinner it won't be nearly as much of an issue.
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Re: Corroded prop bolts

Postby mike.smith » Sat Oct 28, 2017 9:14 pm

lutorm wrote:The prop hub is darkened and slightly crushed. I don't know whether the discoloring is from heat or just the corrosion on the prop flange transferring into the urethane coat of the prop.
Image


According to Sensenich, if your wood prop looks like that, then the bolts have been over tightened, and for a very long time. There should not be an indentation in the wood where the prop flange contacts the prop hub. See the last photo and description on the last page (bottom-left corner).
http://www.sensenich.com/files/document ... 369065.pdf

I'm assuming all the dark materials are the rust from the prop hub, and not friction burns, also described on the last page of the document.
Mike Smith
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Re: Corroded prop bolts

Postby Sonerai13 » Mon Oct 30, 2017 10:40 am

Two things:

First, these are wood propellers. There is moisture in the wood. Installing the propeller MAY result in removing some of the cad plating from the bolts, exposing the bare steel. This WILL Result in corrosion. It pays to check the prop bolts during inspections to make sure they are still in good shape, or replace as necessary.

Second, when installing a wood propeller, you should tighten the bolts until you reach the specified torque OR until you start to physically crush the wood, whichever comes FIRST! Do NOT over-tighten a wood propeller!
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