Wood prop extensions

hohocc · #1 03-15-2013, 01:24 AM

Vans catalogue mentions under wood prop extensions that a 6 inch interface between the extension and prop has proven to be marginal and they have started using a 7 inch interface. I'm guessing the 6 inch was what many older RVs were built with, have owners that used a 6 inch tended to stick with it, and if so what were the issues that made them "marginal", or have most been changed over time to the 7 inch, or indeed some other type of prop?

Gerald Loyd · #2 03-15-2013, 08:22 AM

I built my RV-4 in the 80's and everyone used 6" diameter extensions back then. I am still using it with no problems. I have an O-320 160 HP engine. I think if I had an O-360 I would consider going to a 7". I'm very careful not to over torque the prop bolts and I re-torque them twice a year.

You might want to give the guys at Saber Mfg. in FT. Worth, TX a call. I don't have their number handy. They make most of the prop extensions and can give you the best advice. When I called them they were very friendly & helpful.

Toobuilder · #3 03-15-2013, 08:43 AM

Though I've never flown behind an extension, I did pick one up second hand some years ago. This unit had obviously been operating with the prop under torqued because the face was seriously galled up and the drive lug holes were egged out quite a bit. This is just speculation, but the larger diameter should lessen the clamping requirement some. Perhaps give you a little more margin for higher compression, HP, or whatever. I'm guessing that if you keep on it, as Gerald does, you may not have a problem with either size. Just a thought.

smokyray · #4 03-15-2013, 01:17 PM

Quote:

Originally Posted by hohocc

Vans catalogue mentions under wood prop extensions that a 6 inch interface between the extension and prop has proven to be marginal and they have started using a 7 inch interface. I'm guessing the 6 inch was what many older RVs were built with, have owners that used a 6 inch tended to stick with it, and if so what were the issues that made them "marginal", or have most been changed over time to the 7 inch, or indeed some other type of prop?

Gerald,
I too used a 4" length/6" diameter extension on my RV4 that is still in use after over 2000 hours. The diameter isn't as critical as the bolt size. I recommend no smaller than 7/16" prop bolts. This insures torque reliability between oil changes (when you should check torque every time). If it's already 3/8" you can drill it to 7/16" and purchase new bolts, or....purchase a new extension and bolts from Sabre. As mentioned earlier, my re-drilled, re-bolted 7/16" bolt/ 6" diameter ext is still in use and working fine.

Sabre MFG, world class products:
http://www.sabermfg.com/

V/R
Smokey

jrs14855 · #5 03-15-2013, 01:30 PM

I believe it is generally accepted that 6" is ok for up to 160 horsepower. 7 inch for larger engines. The 0 360 wood props generally have a larger "hub" area than 0 320.

Rupester · #6 03-15-2013, 04:10 PM

... is a GREAT guy to deal with. That's on top of the A-1 quality products they make. I wouldn't deal with anybody else for prop extensions.

Vlad · #7 03-15-2013, 07:44 PM

Another vote for Saber. The thing of beauty...

PropMan · #8 03-16-2013, 07:03 PM

The 7" extension gives something like 36% more clamping area. the bolt torque is typically the same for either and is very critical to maintain. I recommend to everyone a 7" unless the engine is LESS than 150HP. The 6" will get you by, Just make sure the proper bolt torque is maintained, or you'll have a prop catch fire! Ask Sam at Saber. He is my goto person for all extensions and a few other things.