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Tip: Skybolt installation ideas

Fhuber

Well Known Member
I am finishing up the installation of a Sam James cowl on my RV-7A project, using Skybolt fasteners. First I found the Skybolt system to be excellent to work with. The flanges make the install easy and the fasteners are easily adjusted and made to last.
I mounted the prop spinner, using pieces of plastic plumbing pipe as spacers inside the prop bolts. I found it helpful having the spinner installed for line up and spinner to cowling spacing. The Cleko adapters were a big help holding things in place as I worked through the fitting process.
Once I had all the flange/brackets installed and the cowling trimmed to fit, it was time to match drill a hole at each flange for the grommets to be installed. I found it impossible to accurately trace the hole free-hand. So I used a AN-960-416 thin washer for tracing each hole. The hole on the flange is 19/32 in diameter and the washer is 16/32, so the trick is to have an equal margin around the hole with the washer. I used an ultra thin Sharpie to mark both the inside and outside holes. That gave me a bulls-eye to start drilling the hole with the provided Unibit. It was easy to walk the bit to center up the hole as I progressed through the levels of the bit.
The final tip I have to offer was not figured out until late in the process for me. The grommet has a 29/64 inch diameter tube with a 31/64 inch diameter flange on the bottom that holds the locking ring on. The Unibit Skybolt provides has a 30/64 inch step and a 32/64 final step. Skybolt says to drill to 32/64-1/2 step if the grommet will not fit through the 30/64 inch hole. It will not, so I did. What I figured out too late was because of the flange on the grommet you are starting with a 2/32 slop between the grommet and the cowling. If you drill the hole to the 1/2-31/64 size, you now have a 3/32 inch slop. The effect of this, if you have drilled the hole perfectly centered on the flange hole, is to allow your cowling to slide away from firewall to some degree. In my case it required some additional flox to be added along the firewall edge to get the desired spacing. So what can you do to offset this. First, get a 31/64 inch drill bit to make the hole the right size for the flange to fit through. Second, when you mark the holes for drilling, shade the washer towards the firewall a bit to take up some of the slack. You can do the same along the sides if you use Skybolt fasteners along the sides. Overall I have to say Skybolt has made a great product for us to use on our RVs.
 
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