Shims for cowl hinges

I first drilled the hinges to the firewall then realized that the plans called for shims between the hinges and the firewall. So, I went back and put the shims in place now the cowl appears to be below the level of the fuselage skins around the top. Are the shims supposed to be optional? I get a better fit without them and if it is optional I'll not use then.

In my case ...

... the shims were particularly important on the curved side areas.

On the top in the center area, I left out the shims because it looked unnecessary ... much like yours does at this point. Unfortunately, after final riveting the need for the shims became evident. My cowl trailing edge now sticks up noticeably from the fwd fuse skin level.

PeteP said:

Are the shims supposed to be optional? I get a better fit without them and if it is optional I'll not use then.

Click to expand...

Shim "as required" (or not....)

Aiming low - deliberately

I am just putting in these shims now.

I actually considered using thicker shims than the 020 called out (RV 9) so that I could deliberately get the fiberglass cowl below the level of the corresponding fuse skins. I planned to level the two surfaces by glassing over the rivets - which would be a good thing- with maybe just one ply of light cloth followed by micro and clear epoxy to restore a smooth contour.

I haven't done it yet, mainly because I haven't heard of anybody else doing it in the past. More experienced opinions would be welcome.

Pete, if your cowl is naturally below your skins with the standard shims, I think that is something you should welcome and fix as above. However, as Rupester says, riveting the hinges to the firewall is likely to draw the hinge up/out closer to the level of the skin surface. Either way, I would hesitate to leave out the shims - at least the standard ones.

Sam James cowl in my case, by the way.

Hi Pete-
I did not shim b/c during initial fitting it didn't seem like they were necessary. Having said that, after riveting, my cowl does stick up just a bit, though mostly where I used camlocs around the curved part of the firewall. Though it would bother a perfectionist, it doesn't really bother me. Still, if I were to do it again I would shim it because it's easier to build up the cowl to match the skin than it is to remove cowl to match the skin.
Hope this helps. Good luck.

Shims

Thanks for the input. I re-read the cowl section in Vans documentation at lunch time and yes they are marked as optional there. I had not considered the effect of pulling the hinges up tighter when they are riveted vice clecoed. I think I'll leave the shims in at this point in time.

I shimmed per instructions, and my surfaces are perfectly matched. No need to glass over the rivets. I think you will spend more time fairing the glass than the rivet heads. My rivet heads are difficult to locate, but you can find some of them.

Cowl Shim Material

Where did you get 0.020 shim material for the cowl hinges? Vans has .025.