Flex Coupling Drive

[Hughes35]

I've got an atomic 4 with a Walter V drive. Presently there is a rigid coupling joint between the transmission and propeller shaft. I've been having trouble with the flange working loose on the propeller shaft; and I suspect the cause may be from a little mis-alignment. To fix the problem, I believe I need to add a "flex joint"; but I can not find a flex joint to fit the shaft flange. The measurements are: 2.9 inch dia flange mounted using 3 (5/16) bolts spaced on a ~2.2 inch (56 mm) dia centerline and a 7/8 inch drive shaft. Does anyone have any recommendations ?

[Hughes35]

Flex coupling... about to make my own

I haven't heard from anyone concerning a flex coupling between the engine transmission and the propeller drive shaft. Just curious if eveyone already has a flex coupling or if everyone uses a rigid coupling. I ordered a 1" thick sheet of polyurethane and a few 5/16 spacers to support the mounting bolts; when they arrive I'm planning to make my own "flex coupling" on a small lathe. I'll report back as to how well it works.

[Hughes35]

Atomic Four Flex Coupling

Well, I made a flex coupling to fit my Atomic 4 V-drive. It took about 4 hours and seems to be working; but just to be safe, I ran a "finite element" structural analysis on it. The results showed that the flex coupling was "over stressed" and it has a fatigue problem ( it will wear out in about 2 years). Attached a picture of it. There is just not enough clearance, it needs to be at least 4 inches in diameter to cary the load; and I've only got 3 inches of space.

So I designed a second flex coupling using a spline coupling from a tractor. I'll post a picture of it as soon as it's completed. This one is plenty strong enough, but is limited to about 2 degrees of misalignment.

[Hughes35]

Flexible Coupler for Atomic 4

This design seems to be working, still a little too early to tell. I'll know more after a couple hundred hours on the engine. The center is a short shaft with a male spline at one end, and is inserted through the coupler flange than cotains a female spline. The splines are made with .01 inches of clearance which absorbs a couple degrees of misalignment between the flange coupling and spline shaft. I also added rubber pads at each end to keep the parts pressed smoothly together, avoiding any tapping or rattling. [IMG]

[Don Moyer]

To Hughes 35,

Thanks for your perseverance! From all appearances, this coupling should do a good job, and I'm looking forward to hearing how your first hundred hours progress.

I'm wondering if you could provide a bit more detail (part numbers, etc.) in case others would like to travel down the same road. There's quite a bit of interest in flex couplings these days, and V-drive engines are clearly the biggest challenge due to the limited space under the gear box.

A few questions that I would have are (and I apologize in advance if I'm missing something obvious:

1) Is the cylindrical component in the 3-D view (with the Allen-headed bolts) a keywayed coupling on both ends, and is it an integral part of the original tractor coupling?

2) With the splines in the center component of the coupling (again, in the 3-D view) providing all of the flexing, is there any provision to somehow pack the coupling in grease, or is that unnecessary?

3) I'm not too clear on the placement of the rubber stops. I can see one of them between the front of the small splined shaft and the original output coupling, but I'm not sure of the location of the second rubber stop.

4) As a follow-on question to number (3), I'm not sure what prevents the small splined shaft from sliding rearward and out of its flange.

5) Did any of the components require additional machining prior to installation?

Thanks again for your valuable contribution.

Don

[Hughes35]

Flex Coupling

Sorry for the delayed reply, but I've been out testing. I intended on motoring all weekend, but running the engine that long just drove me nuts... I'm a sailor, I ended up with about 15 hours on the engine. Today, I took the coupler all apart to inspect it. The bolts were all good and tight and I could see no signs of any wear... but that is with only 15 hours use. I did have a pleasent surprise, I used to have a wobble that has how gone away. I guess the wobble was caused by the misalignment. Everything ran very smoothly.

To build the Flex coupler, I created a set of drawings and purchased a couple tractor splines ($15) to use as raw material. I gave these to a machine shop and had them make the parts for me. I added a couple O-ring seals, packed everything in grease, purchased a shaft-to-shaft coupler and installed it. The most difficult part was cutting 2 inches off the propeller shaft. To do that, I used a hand grinder with a thin abrasive blade. I put on a set of goggles, and spread a wet rag around the area to catch the hot sparks. It took about 15 minutes and I had to take the grinders "side handle" off, (thread-on) to be able to reach the shaft. I'll keep testing to see how it holds up.

[Hughes35]

Flex Coupling

Well I've now put about 58 Hours on my new Flex Coupling... So far it's still working pretty well.