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
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