Wet dog shake and painted cowls

[Pmerems]

Here is my setup

I have an RV-7A Superior IO-360 with vertical induction Silver Hawk FI, Standard mixture rotation with a straight arm on the throttle body and Van?s standard vertical induction cowl. I also have an offset rodend bracket that attaches to the mixture arm to further position the rodend inboard to gain additional clearance from the cowl.

During fitting of the cowl I estimated that I had about 1/2? of clearance form the end of the mixture shaft to the inside of the cowl and 1/2? of clearance from the mixture/rodend bolt end to the inside of the cowl.

After 40+ hours of phase 1 testing I didn?t detect any interference during the ?wet dog shake? shutdown. A few weeks before taking the plane to the paint shop I notice a small crack in the cowl where the mixture shaft end had impacted the inside of the cowl. I put a small striker plate there and fixed the crack. Flew it to the paint shop and when I arrived there was the crack again and the striker plate had a nice dent in it.

The paint shop said they could graft a blister on the side of the cowl to solve the problem. We agree on an approach and that I was going to send them dimensions of the blister. I left the plane on a Friday afternoon. On Monday I emailed the dimensions and instructions and called the shop. They had already grafted a blister on the cowl. I was surprised and concerned but when I saw the finished painted cowl I was impressed.

Fast forward another 30 hours. While doing my conditional I cleaned the cowl and saw nothing amiss. After completing the conditional I took the plane up for a test flight. A few days later I washed the plane and found a vertical crack in the paint below the blister. It appears the rodend bolt end impacted the side of the cowl and caused the paint to crack. The paint is less flexible then the fiberglass. So it appears the blister wasn?t quite large enough to completely solve the problem.

The cowl looked great but now I need to graft a larger blister to completely solve this problem. The paint shop still owes me a bunch of touchup work so repainting the lower cowl section might be covered.

For those who have the reverse rotation FI don?t think you will not have a problem. The mixture shaft is common to both reverse and standard rotations.

The moral of my story, if you have a vertically mounted Silver Hawk FI on an IO-360 Don?t paint your cowl until you have flown for several hours. You might risk having to repaint it after you have added a blister to handle the ?wet dog shake.?

[Pmerems]

Gents,

Here is a image of my setup.



The photo was taken to document the SB on the Throttle body so the fuel feed line and mixture rodend was removed so I could get a picture of the "G" on the large nut.

I hope this helps someone.

Paul