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piano hinge cowl pins wearing, what to do?

seagull

Well Known Member
Looking for advice concerning the cowl attachment piano hinge. My right lower vertical pin has lost the top two “eyes”. I am getting “smoke” on the paint to the rear of the hinge pin. The top cowl and lower cowl left side pins look ok.

The airplane has 500 hours, is this typical?

Is there a particular vibration I should be looking for that causes this?

I’m guessing there is no simple fix but to replace the hinge half and repaint?

Is there better hinge material that will wear less?
 
If you look back at some earlier threads, the right hinge pin has a history of vibrating up ... yet, the left hinge pin seemingly stays in place. I have noticed this as well and now place the bent portion of the hinge pin under the shop head of a rivet ... which seems to hold it in place. So there is some sort of a dynamic working on the right side lower hinge.

I'm not noticing the wear you mention ... are you using any type of dry lubricant on your hinges? I've always used the waxy Boelube on all my hinge pins.

Since you are missing the two upper eyelets, you will likely want to replace your hinge. Perhaps you can get by without the need to repaint the fiberglass if you first spray paint the heads of the replacement rivets with matching paint for your cowl and let the paint fully cure for a week or two prior to beginning the hinge replacement. When you are ready to replace the hinge, use an Exacto knife and very carefully scribe around the rivets so when they are removed, you won't chip the surrounding paint. (If the assembly instructions were followed correctly, these rivets should be slightly proud which should make using the Exacto to scribe a little easier). Drill out the old rivets, insert the painted rivets and cover their heads with riveting tape and set the rivets.

Sure, you will be able to see the repair if looking closely, but you may be able to live with the results if done carefully. If you don't like the results, you can always paint the entire cowl.

As for stronger hinge material ... Aircraft Spruce sells stainless hinge material. Not sure if it is in the size you need, but they do sell it.

Happy flying,
 
Is the extruded the same thickness or do I need to change both halves? I don't see much wear on the fuselage half.
 
Unusual wear and hing breakage can usually be traced back to one or both of two things.


Excess vibration caused by engine / prop. imbalance (usually eliminated by doing a dynamic prop balance).

and

The cowl being installed with a pre-stress / tension on some portions of it.

During the installation, it is not uncommon for some excessive trimming/sanding to be done on one portion that would produce a gap that the installer chooses to force into position and drill, so as to avoid it.

This puts undue stress on the cowl (and its attach hardware) and usually results in accelerated wear.

This is the reason that the RV-12 KAI cautions against forcing the cowl into a position that it doesn't naturally want to be in.

The longest lasting cowls, are the ones where both halves can be set in position and the pins inserted without having to apply any force to get it lined up. The one exception to this is the left side bottom on the RV-12 because of the need to compress the cooling duct seals at the radiator.
 
Looking for advice concerning the cowl attachment piano hinge. My right lower vertical pin has lost the top two “eyes”. I am getting “smoke” on the paint to the rear of the hinge pin. The top cowl and lower cowl left side pins look ok.

The airplane has 500 hours, is this typical?

Is there a particular vibration I should be looking for that causes this?

I’m guessing there is no simple fix but to replace the hinge half and repaint?

Is there better hinge material that will wear less?

Unusual wear and hing breakage can usually be traced back to one or both of two things.


Excess vibration caused by engine / prop. imbalance (usually eliminated by doing a dynamic prop balance).

and

The cowl being installed with a pre-stress / tension on some portions of it.

During the installation, it is not uncommon for some excessive trimming/sanding to be done on one portion that would produce a gap that the installer chooses to force into position and drill, so as to avoid it.

This puts undue stress on the cowl (and its attach hardware) and usually results in accelerated wear.

This is the reason that the RV-12 KAI cautions against forcing the cowl into a position that it doesn't naturally want to be in.

The longest lasting cowls, are the ones where both halves can be set in position and the pins inserted without having to apply any force to get it lined up. The one exception to this is the left side bottom on the RV-12 because of the need to compress the cooling duct seals at the radiator.

My RV-6 will be 23-years old in September. There are 3,484 flying hours on the original cowl, hinges, and hinge pins.

The only deviation from the plans during build was replacement of the bottom cowl to fuselage hinge being replaced with metal plate, nutplates, and #10 screws.

The cowl hinges and pins have all held up very well for me and echos Scott's comments.
 
My pins are curved to the cowl, they all insert easily. I clean them each time they are removed and put Boelube on them every time. The lower sides and rear sides (short ones) have the legs go under the rivets to keep them from lifting out.
Tomorrow I will check the balance on the prop.
 
I had a friend help me with the prop balance today. It was at .16 IPS when I started, which isn't that bad, but we played with it and finished up at .06 IPS. It was a noticeable change in flight. I am sure it will make some difference on the hinge wear, but not sure if it is significant.
 
I could not get my pins in place so I used 1/16” weld electrodes the first 500 hours. They vibrated and wore on the eyelets so that I could then get the hint wires in. Since then no issues.
 
This was going to be a temporary solution, I did not want to rivet and repaint to replace the hinge half. After doing the work and flying it for 30 hours I am extremely happy with the repair and see no reason to replace the whole hinge.

I got extruded hinge material from Spruce. Cut a piece with the requires "eyes" (3) to replace the worn out ones, I added the flat area length to extend to the next good eye. I located the rivets and made relief holes in the new hinge piece. The new piece was mounted "upside down" so the natural angle of the eyes were toward the outside. I had used a vice and wood block / mallet to slightly reduce the offset to the eyes so they would line up with the existing hinge. Once happy with the fit and freedom of the hinge pin, scuff up the face of both hinges and JB Weld them together, clean up the excess glue and paint.

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If you turn the “L” 180 it will lock under that rivet tail. All 4 of mine are done that way and never come loose. No need to add anything else.
 
I started with 3/32” weld rod, but after several years vibration opened up the piano hinge holes and I can now use the hinge pins. A little oil on the pins helps, but don’t freak out when oil droplets form at the seam between the upper cowling and avionics bay cover.
 
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