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Building a Bump-out on lower cowling

Ottoman

Member
I can't find a thread on this so I'll raise the question?

I'm building a 7A, IO360-M1B, with FM 150 intake, problem is the mixture cable hits the cowling. I sanded down the honeycomb covering in that area, a small spot, and it doesn't touch anymore.

But with engine shake I think it will rub on the cowling! My thought is to build a bump-out. The question is how big and how much room dose it need? Are there any pics out there?

Thanks,
John A.
 
Bump wise a 1/4 or 3/8" clearance should be plenty, a tear drop shape or long gradual raised ridge looks much better than a wart.
 
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same cowl

I have the same cowl and injector body.

I was going to try and reposition the arm back more. It interferes so little. But if this doesn't work, my other options is to find a=n arm that doesn't sit out as much (closer to throttle body); or do a bump like you are talking about.

I am closely following your dilemma and solution.
 
Use a hole saw to cut out a clearance hole. Insert a 100 watt light bulb on the inside of the cowling. The fat side aimed out. Tape into position then on the outside apply several layers of fiberglass. When the fiberglass has cured you will end up with a nice looking bump. Remove the light bulb if it is stuck smash it and clean out the bits of glass.
 
Mold

Use a hole saw to cut out a clearance hole. Insert a 100 watt light bulb on the inside of the cowling. The fat side aimed out. Tape into position then on the outside apply several layers of fiberglass. When the fiberglass has cured you will end up with a nice looking bump. Remove the light bulb if it is stuck smash it and clean out the bits of glass.

Enlightening tip. Sorry, couldn't resist. Actually quite brilliant. Ooops. I use all sorts of stuff. Just wax the **** out of it and the mold will come right off.
 
Better yet

Better yet, put packing tape over the light bulb and fiberglass cowling surrounding it. Fiberglass over the whole thing and drill two or three 3/32" cleco holes to hold / align this new fiberglass piece. remove the fiberglass piece, and the light bulb. Scarf the inside of the cowl, wax the new fiberglass piece and layup you final piece from the inside overlapping the cowl. This way the first fiberglass piece becomes the form, and the final fiberglass bump is as smooth as the bulb; very little finishing.

Do you really think 3/8" is enough clearance for the wet rag shakes?
 
Different model but on my -10 I had to make a bump out for the exhaust. I built up with expanding foam (sanded the shape I wanted) on the outside, then sanded off the honeycomb with a angle grinder. Once the clearance was sufficient I applied layers of fiberglass (on the outside) to build back the cowling. The sanded out all of the expanding foam and put a couple fiberglass layers on the inside.

http://www.strikhedonia.com/cowl-finishing-day-uno/
 
Bump-out

I like the light bulb idea, I'll try that tomorrow.

Here's the mold I made today!
I hope the pic shows up, this is new to me.
 

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A guy on eBay sells various sizes of aluminum teardrops. I selected one and used it as a female mold and vacuum bagged it with my wife’s Press-and-seal. Came out great.
 
Balloon

I've used balloons before as molds too. If you can keep it from popping, it works great. After the fiberglass sets up, just pop.
 
I have a Precision Airmotive Fuel servo and used a bump out of about 1” . Also fabricated a bump on lower right side for the alternator pulley. After cutting the cowling for the bump out, I used a foam block shaped for each cowl modification of the fiberglass. This is the only photo on my iPad but you can see the fuel servo modification.
 

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Metal

If there are metal teardrops on amazon, why not just use those with fiberglassing over?

Will there be a problem if the metal teardrop is fiberglasses into the cowl? Will the dividing line tend to crack the paint?
 
Metal

If there are metal teardrops on amazon, why not just use those with fiberglassing over?

Will there be a problem if the metal teardrop is fiberglasses into the cowl? Will the dividing line tend to crack the paint?

I used thin aluminum to stiffen the area around the oil door opening inside. I bonded the aluminum sheet with G-Flex. Then the opening was cut out and a layer of fiberglass layed up over the aluminum. It's not going anywhere.
I would do similar in your situation. Cut outbthe shape and bond it inside then glass over the outside.
 
Bump-out

The light bulb, and the balloon idea were good idea's but didn't work Me.

So I stayed with my original idea, four layers of glass over a clay mold. This accommodated the hole that I thought I needed.

Light, to highlight the hole before attaching.
 
Better solution

So I found a better solution to my problem with the mixture arm hitting the cowl on my Avstar AVX-NNSS5.

I am going to replace the mixture arm that came stock from Lycoming, with the straight version; no need for a bump in the cowl.
 

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