Lost two teeth
 

I have now lost a second tooth on the piano hinge at the bottom right side of the lower cowling at the firewall. I have searched the threads and noticed that this is a common problem after various numbers of flying hours. I have about 225 hrs. on my 9A.

Various solutions include camlock fasteners or screws or replacing with a new piano hinge. I am thinking about using screws into nutplates on aluminum lip riveted to the bottom firewall flanges. If this is a good solution, how many screws on each side of the bottom cowling are recommended?

All other piano hinges on the top and sides are still looking good, so I am just thinking of using something different on the bottom. Any and all suggestions will be appreciated. thanks, jack :D

On my RV-7 I have four #8 screws per side, eight #8 screws total, going into nutplates in an .032" thick flange extension. I know some people use thicker flanges here, but I know at least two -6A drivers who broke .063" thick flanges in this spot. I'm a believer in a slightly thinner one in this particular area.

I countersunk the cowl flange and used tinnerman washers to spread the load. No issues and no broken eyelets on the side/top hinges in ~1400 hours.

I used one #8 screw per side on the inboard edge and left the hinge and pins in place. This holds the cowling up at that point not allowing it to hang on the hinge. I pop riveted a piece of angle onto the firewall for a nutplate. This is what Vans does on thier airplanes and it works well.

Pic?
 

Hi JonJay.

Do you think you can post a pic of your installation with the #8 screw?

Thanks!

Regards Alf Olav Frog / Norway

thanks
 

Dan and Jonjay: thanks for the replys and suggestions. 1400+ hours on Dan's 7 is pretty good evidence that the screw method works. I'm wavering on whether to add one screw and keep the piano hinges (per JonJay) or drill out the piano hinges and put 4 #8s on both sides. Both seem like good ideas. May do the JonJay suggestion for now, and replace the hinges at the next annual when it's cooler. 101F and humid today.

Personally, I think one screw in the inboard corners would serve the purpose just fine. If I already had hinges, that's what I'd do. Least amout of work to serve the purpose.

i was afraid you got hit by flying clecos. ;( POW!

I did what danC mentioned after the first riveted repair didn't hold on my lower left cowl.

edit-- actually what build9a did because i put about four screws in the lightening holes I already had in the piano hinge anyway.

Extruded hinge
 

I replaced mine with bigger extruded hinges verses the rolled hinge they sell. On second thought it may have been about the same size as original just the higher quality extruded hinge. In the same cowl I used #8 countersunk screws and tinnerman washers but not at the bottom side.

There is tremendous pressure pushing up on the front of the cowl from the out side and inside with the upper plenum. A fixed top plenum that does not rely on the cowl to direct internal air down into the engine will help also.

good move george, i did the same thing on the rocket.

the hinge supplied by van's looks like Chinese quality throw away metal compared to the extruded hinge; avail. at ACS.

i would have never used that on my 7a had i seem the military spec hinge.

Wonder if there's a pattern
 

I, too, lost exactly 2 eyelets on the bottom cowl hinge of my 7a. That happened at about the 50hr mark. It's been on my list to address since then - but haven't gotten around to it. Now at over 300 hrs, without any further eyelets letting loose. This would lend some credibility to using just the single nutplate method on the center side of the hinge.