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DIY Cowl Installation Jig

HFS

Well Known Member
Here are a couple of pics of a cowl installation jig I made out of PVC 2 1/2"Sch 80 pipe & 1/2 PVC sheet.

The beauty of using the PVC Sch 80 pipe is - the i.d. is ~2.257" which is very close to the pilot diameter of the crank flange - 2.25". If .007" clearance is a bother - a single wrap of green masking tape around the pilot solves that problem.

The posted minimum wall thickness of 2 1/2" Sch 80 PVC pipe is .276", but I have found the section(s) I got from McMaster had a wall thickness of .309", which yielded the i.d. of 2.257.

The PVC is very easy to machine, and plenty "tough" enough for this job. Slow turning, pretty large cuts - and keep it cool. The last one I made had a run out of .008" - good enough for "Government Work". The hole pattern for the prop bolts doesn't have to be very accurate - just enough to clear the lugs both radially and height wise - the pilot/register arrangement give the accuracy.

The "disc" is the same size as the spinner and is used to center the cowl (either together or halves) on the crankshaft. Once the disc is temporarily installed on the cowl, it can slide over the pipe mounted to the crank flange, giving perfect alignment every time it is re-installed.

I have developed a (detailed) 5 page instruction manual for its use - comes in handy to know where you are going before you head out in the dark!

I have used this system, in one form or another for many years and it always works well for me.

Sorry about the quality of the second pic - taken by Polaroid in 1999.

YMMV

HFS
 

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Beg, Borrow or steal

So I am currently caught in the wiring maze (quite literally sometimes) but would like to borrow this in a few months once i find my way out of the harness shop. Could I borrow one, buy one, or?? I have an i0320 new from Vans.
 
Cowl Installation Jig

I think, subject to interest, Blake at FlyBoy Accessories is considering producing them as a less costly alternative to their "professional" model.

HFS
 
I am planning to fit the cowl on my RV8 now most of the engine/electric related work on the firewall forward is completed. I would like to get the instructions to build and use the parts.

I am sending you my contact info via PM.

Thanks
 
Howe Jig

I am writing a draft on the cowl install using his original jig. It's on my blog.
Also redoing his drawings in CAD for sharing with his permission.
 
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I used the aft half of an old Hartzell hub (no blades) to fit the last two cowls. I compared it to the hub on the new Hartzell prop and it is identical. Mount the spinner backplate to it, then the hub to the engine.

If you can get your hands on one (as in someone has a wall hanger bent prop in the hangar or such) it makes for an exact cowl fitting tool.

Carl
 
Faux prop

I used the aft half of an old Hartzell hub (no blades) to fit the last two cowls. I compared it to the hub on the new Hartzell prop and it is identical. Mount the spinner backplate to it, then the hub to the engine.

If you can get your hands on one (as in someone has a wall hanger bent prop in the hangar or such) it makes for an exact cowl fitting tool.

Carl

Some prop manufacturers will rent or let you borrow a faux prop hub. Whirlwind has one. Nice way to make sure the cowl is correct.
 
STL File for prop hub

Does anyone have an CAD drawing of the prop hub? Many of us could make a 3D shape for the hub for our 3D printers. Or if there is someone that already has a STL file, can you share it?

Phil
 
Jon Thocker, Ken Reider, and I bought the FlyBoys jig several years ago together at Oshkosh. We are at the same airport. I’ve used it twice, Jon used it, and Ken used it - about to use it again on his new RV8 build. Several other guys at our airport have used it. It makes the fit mush easier and more precise.

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You just need to know the distance between the forward side of the crankshaft flange, plus starter flywheel to the back side of the spinner, then subtract whatever gap you want between the forward cowl face and your spinner. Lock that dimension on the jig, and mate the cowl to the round plate (clecoe it) and make your trims to the fuselage/firewall. Easy - peazy.
 
Cowl jig

I have David's original drawings. I really think the jig can be assembled pretty easy as designed with Schedule 80 PVC. Minimal cost.
Of course, the Flyboy jig is always an option.
The jig in either flavor is a pretty awesome time saver.
 
Currently working the cowl with his set up. Super nice guy. I have some of it in cad already if any needs it.
 
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