Engine Cowl Fastener Hole Repair

EJWash

EJWash

Active member
Joined
Aug 11, 2021
Messages
42
Location
KCLM
While in annual ('75 8KCAB) my mechanic advised that the lower engine cowl fastener holes are *way* worn. These are the holes that attach the cowl at the firewall. He suggested either replacement, or repair. Repair (material/labor - mostly labor) was going to come close to replacement. He asked if I'd like to take a whack at repairing it myself. Why not? I have some, although limited fiberglass experience (marine).

The plan is to grind/abrade a 2" area along the firewall edge of the cowl, and lay in a 2" strip of new cloth using epoxy. I haven't worked out how to go about filling the mounting holes. I need to enlarge the holes a bit, for new material adhesion, since grease and oil has made its way into the raw edges of the holes. At present, I'm thinking using West System 404 high density filler. That stuff sets rock-hard.

Wondering how others have tackled this situation. Thanks.
 
I had this same problem 20+ years ago all the way around the upper and lower cowls and converted from the dzus fasteners to #10, 100 degree countersunk machine screws with 3/4" dia countersunk washers and floating nut plates. Two layers of 2" glass cloth were added to each side of both cowls to reinforce them. I was pretty proud of my "improvement" but later noticed that the newer ACA Citabrias appeared to use the same idea. Incidentally, this has worked well for a long time and eliminated fighting with the @!**! dzus fasteners.

It might be a good idea to take a look at a newer Citabria and see specifically how ACA accomplished it.

Paul
 
I tapered mine back about an inch, inside and out. Then layered to bring back flush. I considered adding more glass, but the original lasted 40 years.IMG_20220226_142706_HDR (1).webpIMG_20220406_160214_HDR.webp
 
Thanks fellas. I should add that I'm shooting for minimum impact to the exterior of the cowl. I understand that the most effective route would be to grind down 360-degrees around the existing holes, both on the interior and exterior, and lay in and build up new cloth. I'll address the repair from the interior for now. No logbook history of the cowl being replaced, so I'm guessing it's the '75 original. Gonna need new fabric in a few years anyway. Will replace the entire cowl then. For now, need it airworthy.
 
I bought a "Bondo Fiberglas Repair Kit" in a box at a local auto parts store. Both the fabric and the resin seemed to be suitable for a couple of cowl repair projects which have lasted for years. I'm planning to buy another kit to repair the busted fenders on my airport golf cart.
 
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