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nicholson31 · 10-12-2015, 08:59

My prop drive shaft and split coupling presently has a keyway installed. Can I replace my old split coupling that has a keyway, with a new split coupling that is not keyed?
I don't foresee any issues but advice from the experiance forum please!!
Currently sourcing one through ASAP supplies, UK and it appears to have a machined threaded hole for a stop stud to pass through and contact the shaft, as does the old coupling, which should help prevent rotational slippage or shaft sliding out, but not keyed.
Has anyone switched these out from keyed to keyless and kept the same shaft?
I have not come across any 4 inch split coupling (1" shaft) on line, that accommodate the keyway like the old one has. Also If anyone can recommend a supplier for such an animal I would prefer to go with the keyed coupling type.

mike d. · 10-12-2015, 09:12

What is the reason for not wanting keyed coupling? I can't imagine that compression coupling would work any better. Also I don't know if you can change to a compression coupling with that shaft. You would be loosing bearing surface, and also compression stress riser, I would think, because there is surface contact, where the key would have sat!

nicholson31 · 10-12-2015, 09:47

Its not a compression coupling i'm replacing it with its another split coupling, but it does not have the keyed slot!! I have so far only seen the keyed in 5" and larger
couplings.

wrwakefield · 10-12-2015, 10:12

Quote:

Originally Posted by nicholson31

Its not a compression coupling i'm replacing it with its another split coupling, but it does not have the keyed slot!! I have so far only seen the keyed in 5" and larger
couplings.

Nicholson,

It is not a big task for a machine shop to mill a keyway in your new coupling that matches the size of the existing key.

Edit: I would be hesitant to rely on a driveshaft that is not keyed... a set screw won't provide the surface area required if you had the prop stopped suddenly by something while motoring, and may loosen over time ultimately galling your shaft. A through, tapered shear pin would be better than a set screw, but not as good as a properly sized key. [Straight or Woodruff key...]

I would ask for some estimates from any local shops.

Specifically, if the portion needing the key is one piece [i.e., if each half of the coupling is a single piece that slides over the end of the shaft] then you need to ask if they can 'broach' a keyway for you.

If each half of the coupling is split so there are two halves that clamp over a shaft in place [i.e., the shaft doesn't have to be inserted in a hole] then it is even easier; you will ask if they can 'mill' a keyway for you.

This shouldn't cost that much if you find the right shop to work with...

Cheers!

Bill

jimbunyard · 10-12-2015, 10:19

There are many manufacturers and suppliers, Buck Algonquin comes to mind. Here's a couple of suppliers:

Buck Algonquin, Transmission, Shaft Couplers, Spilt

Buck Algonquin 50400A1000 | Fisheries Supply

DougR · 10-12-2015, 10:34

Suggest you try Walters Machine Co. in Jersey City, NJ or Buck Algonquin. Both of then make split couplings with keys, and can be found on the Internet.

DougR

rbyham · 10-12-2015, 10:45

I have purchased from buck and bought keyed for 1" shaft. Also use steel not bronze key. No way set screws alone can handle the torque.

nicholson31 · 10-12-2015, 11:25

WRWakefield: The coupling as listed with ASAP supplies is milled steel and is one piece with the split on the aft half of coupling 2 clamping bolts per side.
I do have a flex coupling installed for those sudden stoppages, which I have experianced and they do work.
I am an ex aircraft mechanic and constantly checking everything, probably annually, so I would most likely notice any signs of slipping with the keyless coupling but yes, confirming with a local mil shop of cost to modify coupling is a good suggestion thanks.

JimBunyrd: I did look at those suppliers but not sure if they are keyed either according to website, will have to call. They are also cast iron as apposed to milled steel which is, i guess why they are half the price.

A member at our club lost his shaft due to new coupling sliding off this past summer, boat washed up on the rocks and sunk they were rescued.
No room for compromising here.

nicholson31 · 11-12-2015, 03:26

From the few responses on the subject I will come away with the advise of ensuring its replaced with another keyed coupling weather from the OEM or I have it modified.
The only thing about the cast couplings from Buck Algonquin is that they appear to only have 2 crimp bolts as apposed to 4, picture on website.
If I can have the milled steel coupling from ASAP keyed for a decent price I will swing that way as it has 4 crimp bolts and milled is much better than cast. Either way survey says "Keyed" all the way!!
Thanks for imput folks

Still would be interested to know if the keyless split couplings that just relying on the crimp bolts do hold up under heavy torque?

,

wrwakefield · 11-12-2015, 12:40

Hi Nicholson,

I agree with your choice of a solid steel milled coupling. I wouldn't be surprised if they are sold without a key-way intentionally because there is no guarantee that the shaft has the standard size key for that diameter.

Hopefully you can find a reasonable machine shop that can accommodate your needs.

Cheers!

-Bill
SV Denali Rose

deblen · 11-12-2015, 12:54

Some more info:

A New Prop Shaft Photo Gallery by Compass Marine How To at pbase.com

Cheers/ Len

Nicholson58 · 12-12-2015, 04:45

Quote:

Originally Posted by nicholson31

My prop drive shaft and split coupling presently has a keyway installed. Can I replace my old split coupling that has a keyway, with a new split coupling that is not keyed?
I don't foresee any issues but advice from the experiance forum please!!
Currently sourcing one through ASAP supplies, UK and it appears to have a machined threaded hole for a stop stud to pass through and contact the shaft, as does the old coupling, which should help prevent rotational slippage or shaft sliding out, but not keyed.
Has anyone switched these out from keyed to keyless and kept the same shaft?
I have not come across any 4 inch split coupling (1" shaft) on line, that accommodate the keyway like the old one has. Also If anyone can recommend a supplier for such an animal I would prefer to go with the keyed coupling type.

I design machines. The preferred best method in this case is a key. It will never slip. It should be a minor deal to get a machine shop to cut a keyway for you.

If you choose to use a set screw instead, be aware that the torque capability will be less than with a key and if the screw vibrates loose it will slip and score the shaft. When we use set screws we normally dimple the shaft so the screw has a better bite. You may also have enough thread depth to run a second screw into the first screw similar to a double nut on a bolt.

malbert73 · 12-12-2015, 05:13

I would use a key. Funny story, though: when we were surveying my tartan 40 in 2014 pre-purchase, the engine surveyor noted that there was some rotational play where the shaft entered the non-split coupling. It was thought that the shaft keyway was worn. We factored new shaft and coupling as part of negotiation. When yard took everything apart, they found the key lying in the bilge beneath the transmission, and the shaft was only held by 2 set screws that were in 2 dimples on the shaft.
The prior owner probably was horrified to hear that for the 4-5 years he cruised with the boat, the only thing holding the shaft in the boat was the two tiny set screws as whoever installed the last shaft must have dropped the key inadvertently while installing the shaft... 44 hp 4jhe and 3 blade prop so decent torque on the shaft.

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