Help with changeout from Hartzell to WhirlWind 74RV

[CopterJohn]

I have built my RV6A around a Hartzell HC-C2YK-1BF that came with my engine off a Husky. Cowling is fit and painted. AD hit my prop, so I splurged and ordered the Whirlwind 74RV based on excellent past experience with the WW200 series on an RV7.

Installed prop and went to cowl up and both the upper and lower cowl impact the angled backplate and are wedged against the rear of the spinner.

Thoughts? Anyone else changed out a Hartzell for a WW and had issues with spacing. I sure hope I don't have to trim the cowl now that all the hinges are on and had nice spacing with the Hartzell club. copterjohn@gmail.com

[chazking]

Shim the mounts, remove excess material where the backplate overlaps, replace backplate screws with 100? offset machine screws so they're flush, and remove the cowl edging to backplate areas as necessary for clearance. Reinforce cowl areas being sanded as necessary.

No matter how you do it, it's a PITA! The prop will look super when you've finished.

[RV7ator]

I changed a C2YR for a 74RV on a -7. Simply cut away the inside flange of the cowl behind the spinner, leaving a round opening to clear the tapered spinner bulkhead and screws.

Backplate/cone-to-cowl is a whole other problem. I saw the gap was going to be closed 1/16" based on Whirl Wind's installation drawing, so had them relieve the aft edge of the bulkhead and cone; 1/16 is about the most they can trim, but it might save you from cutting back and refinishing your cowl face. Talk to them about modification.

John Siebold

[Steve Melton]

I reinforced the cowl front face top and bottom on the backside and then cut the front face of the cowl leaving about one inch all around. Probably not what you wanted to hear.

[CopterJohn]

Shim the mount at the ears with washers behind the bushing or at firewall?

[RV8iator]

Originally Posted by CopterJohn

Shim the mount at the ears with washers behind the bushing or at firewall?

I tried this once with a different prop and created all kinds of problems with alternator, induction, baffles, cables etc. I never would have thought that moving the engine forward between a sixteenth and an eighth of an inch would have created that many problems. I put it back like it was and worked on the cowling on that one.

On my first change to a WW200, I measured the exact spacing and WW made me a special backplate that fit perfectly. You may want to go that route now, though they will undoubtedly charge you some for redoing the spinner.

[CopterJohn]

Thanks everyone...
JM

[dstew]

I had the same issue when switching from a 3 blade MT to a WW RV74. A hanger neighbor happened by and 1hr later delivered 4 5/16 machined shims.
I installed them between the firewall and the engine mount. It did require a different prop cable as the original was stretched and had no extra length.

Dale

[gereed75]

One option may be to fill the back side of the round section of the cowl solid with an epoxy glass mixture of your choice. You could make it say 1/2 inch thick. Then you can go to the front side and sand it back into the thickened section the amount that you need to provide clearance to the spinner. This will require a paint touch-up but is other wise very easy to do - no cowl cutting or re-sectioning needed.

[edsong]

Call Saber and ask about a prop extension. Easy bolt on solution.