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cowling fastener puzzle

J

jay.pearlman

Well Known Member
I am installing your skybolt fasteners in the cowl of an RV that I am building using the James cowl. For the top half of the cowl at the firewall, I drilled the cowl fastener holes to 15/32 rather than the 1/2 inch recommended in the sky bolt plans. The grommets for the retainer 1/4 turn screws seem to fit well in this size hole. Is there any reason I should drill out the hole to 1/2" as suggested in the skybolt instructions?
Has someone else done the slightly smaller hole?
 
I also drilled the holes at 15/32" with a unibit. The James cowl fits fine as I have had it off and on about 30 times during the build process.

The larger holes will allow a bit more slop and may ease the installation slightly but you can always drill them larger if I needed.
 
A local builder who used Sky-bolts passed on some "O" rings when he finished.
The "O" rings work well in place of the retaining rings till after painting when the more permanent rings can be installed.
 
I used the grommets for final fit

and just removed the snap rings and grommets for prep and paint. Not too hard to remove them, but don't be surprised if one or two fly across the room.
 
it works

Terry,
I put on the grommets and the snap ring. Then scratched my head a bit. With a dental tool I was able to reach under the opening of the snap ring and off it came. Even managed to hold onto it. That may be beginner's luck. I used the holes at 15/32 dia in the cowl and they are fine, although paint may make then tighter.
Thanks everyone.
 
hole size

Ned of Skybolt sent a note answering my question of hole size. If you have the step drill to make the smaller hole and the grommet fits, use it.

He also explained some of the operations/benefits of camlocs. to quote:
What this really means is that the stud snaps outward as it sets in the locking area about .020 such that the face of the stud is flush with the face of the grommet. To go a bit further, you actually have a shock obsorber with a .020 stroke. In other words, spring pressure is clamping pressure. A bolt/screw/hinge is a solid clamp. A 1/4-turn has clamp pressure, thus, history will tell us, the cowling will last forever because it is shock relieved (aluminum cowling under tremendous vibration). That is a WWII discovery with the Dzus fastener. Prior to the Dzus design, cowlings were bolted to the airframe. If a R1830 was good for 2 combat missions, the cowling was only good for 1. The Dzus fastener changed all that and those cowlings are still flying today.
Thanks for the engineering insight.
 
1/2 in. cowling holes

Dont drill the 1/2 inch holes as recommended, I have had problems with play and and have been nervous with them ever sense.
 
jay.pearlman said:
Did you wait until you painted to but the rings in or ?
Click to expand...
A really easy solution to this problem for me was to not use the supplied retainer rings that are a real pain to get off intact but to buy a package of 50 snap rings from Grainger for $5.00, delivered, to my local store. Once I paint I'll use the original retainer rings but, until then, the cheap snap rings serve the purpose.

FWIW, my camlocs are Milspec. I would think Skybolts would be similar. I purchased 1/2" snap rings but next time would probably go down to a 15/32 or 7/16 b/c the 1/2" ones are a bit on the loose side. Even with 1/2", however, the ears of the snap ring do not at all interfere with the camloc receptacle.
 
Until I paint, I am simply removing the fasteners when I remove the cowl. My cowl is a pain to install. I am thinking if I have the snap rings on, I will be doing a lot of paint scratching installing and removing the cowl.

Any comments from those who have had them on awhile regarding paint scratching?
 
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