Belleville Disc Springs

Any of you installed a wood prop and utilized Belleville washers/disc springs? The FWF kit I got from Jabiru USA included 12 Belleville Disc Springs listed as  "0.625 x.317 x .032" and 6 AN-6 prop bolts. After installing the spinner backplate, prop, and crush plate, you're supposed to put 2 of the disc springs (concave sides facing) on the end of the bolt, then a washer and the nut. As I understand it, the wood prop is subject to expansion and contraction with temp and humidity changes, so the disc springs compensate somewhat to hold the torque better.

Problem is, the disc springs' hole is .317" diameter which is essentially identical to the thread groove diameter on the AN6 bolt. How do you get the darned things on the bolt? They're waaay too tight to slip over the bolt. I tried threading them onto the bolt, but I can't get them to take a "bite" and run up the bolt. Jabiru tech support isn't available until Monday, so I thought perhaps someone in the forums has "been there, done that".

Thanks,

John

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Permalink Reply by John Austin on January 13, 2012 at 9:19pm

Well, this Belleville disc spring issue is getting a little more confusing!

I did some further Googling and found a thread where Pete at Jabiru USA says that the Belleville disc springs are available from McMaster-Carr, stock no. 9712K68. When I looked them up, the good news is that they're relatively inexpensive and have an i.d. of .380 - that would, of course, easily go over AN6 bolts! Clearly, the supplied Belleville's are too small!

HOWEVER, I also found a thread that said Jabiru (Aircraft Co.) uses them because "their Australian props are made from a softer wood - you don't need them for most US props" !!!

Since my prop is a Sensenich, I went through their installation recommendations and sure enough, they don't mention Belleville disc springs at all! But, to compound things further, the instructions DO mention safety-wiring the prop bolts' nuts. (The nuts supplied from Jabiru USA are lock nuts.)

Sooo, I think next week I'll just talk to Sensenich and double-check I don't need the Belleville discs and determine whether the lock nuts are OK or whether use drilled bolts and safety-wire them.

"It's always somethin' "

John

Permalink Reply by Ralph Sanson on January 14, 2012 at 2:50pm

Your'e so lucky to not be using a Jabiru prop, because the JSB 009 shows how to install all 48 of those washers.

I did the mod for a short time but had to replace the prop when it warped out of limits and put a Brent Thompson on.

Just read JSB 014 which covers properly made props. Nyloc nuts appear perfectly satisfactory on mine although I wonder if they would meet AC43 methods. There is very little about the Jabiru which does.

Ralph CH701 / 2200a

Permalink Reply by John Austin on January 16, 2012 at 4:36pm

Here's a follow-up:

I called Sensenich today and they said they neither recommend nor require the use of Belleville disc spring washers with their wood props. Tech support said nylon locknuts, plain washers and the crush plate was all I needed to use.

John

Permalink Reply by Bob Pustell on January 17, 2012 at 2:48pm

Here is a very detailed piece by a Cozy builder who make a strong case for bellville washers on wood props. It makes an interesting read, even if you end up not going along with him. Lots of info.

http://cozybuilders.org/Prop_Bolt_Bellville_Washer/index.html

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