Propshaft spinning in spline

[Conrad]

I have a problem with my propshaft spinning in the spline that holds it connected to the gearbox.

The spline is a simple clamp that tightens around the propshaft with four bolts, there is no woodruff key or pin it just relies on the force of the grip.

Unfortunately I found this out when I drifted onto a mud bank and no matter how hard I tried to tighten the bolts it still would not hold the propshaft and drive the boat, the RNLI who were about very kindly offered me a tow so at least I got home without to much bother.

I will be replacing the four bolts as a matter of course in case they are stretched, I was wondering if anyone had any similar experience and whether there are any proprietary fixes out there, I am thinking of locktite or something similair.

I suppose I could always drill and pin it but this may be a bit difficult on a swinging mooring trying to go through a stainless shaft.

 

[Conrad]

I meant spinning in coupling.

 

[Bejasus]

I am sure that others will be along soon with better ideas, but on our first boat we had the same arrangement with a split coupling. It had also been shimmed inside and drilled through the coupling and into the shaft and a grub screw fitted. I guess in the past a previous owner had a similar problem.

 

[Kurrawong_Kid]

Had this trouble too! Motored into a strong head wind and couldn't understand why I needed such high revs. When I later investigated the polished shaft gave the game away. Fortunately I was able to tighten the bolts. I thought there was supposed to be a grub screw with a point that should be screwed through a hole in the coupling on to the shaft as well, but that was missing. Perhaps the engineer forgot to fit it?

 

[Tranona]

Should not normally need anything other than the 4 screws - often the problem is the reverse ie difficult to move!

If the bolts are up tight then it suggests that the shaft or the coupling is worn. Suggest you take the bolts out and slide the shaft back if you have room to check the end of the shaft and the coupling. Put a jubilee clip on the shaft to stop it from sliding out completely!

 

[Cliveshep]

I have a problem with my propshaft spinning in the spline that holds it connected to the gearbox.

The spline is a simple clamp that tightens around the propshaft with four bolts, there is no woodruff key or pin it just relies on the force of the grip.

Unfortunately I found this out when I drifted onto a mud bank and no matter how hard I tried to tighten the bolts it still would not hold the propshaft and drive the boat, the RNLI who were about very kindly offered me a tow so at least I got home without to much bother.

I will be replacing the four bolts as a matter of course in case they are stretched, I was wondering if anyone had any similar experience and whether there are any proprietary fixes out there, I am thinking of locktite or something similair.

I suppose I could always drill and pin it but this may be a bit difficult on a swinging mooring trying to go through a stainless shaft.

With the shaft spinning inside the coupling it suggests wear between the faces of shaft and coupling so that the coupling can no longer grip. A cheap solution might be to clamp over a bit of emery cloth (not wet and dry) with the grit face against the shaft. Get hold of a centre punch and hammer and abuse the shaft first to rough it up a little.

Of course, if you have loads of spare dosh, try a new coupling but I know what I'd do!

 

[cliffordpope]

I've always been impressed that these things work so well normally without any kind of key or grub screw. Could the slipping be because the bolts have run out of thread and you are tightening against the shanks rather than tightening the actual clamp? It might just need 4 washers.

 

[Conrad]

Thanks for the suggestions so far.

 

[sailorman]

drill through the

coupling & shaft & drive in a "Roll Pin"

 

[jason -and the arguenauts]

you didnt say what sort of power your shaft was transmitting but in a typical 20 hp sail engine I wouldnt think twice about drilling through the coupling and into the stainless - then tapping the hole and inserting a machine screw.

But the first thing to check is that the shaft is fully into the coupling ( ie no one has put it half in the accommodate a shaft cutter) and that the bolts arent binding on the shoulders.

Any such shaft should have a pin or a keyway - its a shortcut just to rely on friction.

 

[30boat]

you didnt say what sort of power your shaft was transmitting but in a typical 20 hp sail engine I wouldnt think twice about drilling through the coupling and into the stainless - then tapping the hole and inserting a machine screw.

But the first thing to check is that the shaft is fully into the coupling ( ie no one has put it half in the accommodate a shaft cutter) and that the bolts arent binding on the shoulders.

Any such shaft should have a pin or a keyway - its a shortcut just to rely on friction.

My Aquadrive coupling has no key or grubscrew.As long as the mating surfaces are good and the coupling is well tightened it will work.

 

[DownWest]

Apart from the above about bolts bottoming or binding on their shoulders, check there is still some 'nip' left between the faces of the coupling. Some work with the angle grinder will improve this. A bit of Loktite won't hurt after swabbing with cleaner. Clamping friction should be enough without keys or screws. But the shaft and coupling must be not too grooved or worn.
A

 

[Conrad]

I'll probably go for drill and pin, but will have to do it in situ on a swinging mooring.

Drilling stainless sounds quite daunting has anyone had any experience of this, any tips, is it doable?.

 

[jax]

I'm with Downwest's solution. IMHO you are going to have a job drilling the shaft in situ and I would rather have the shaft free to 'give' if the prop becoomes fouled than something having to break (the pin) or even to move the engine, I have a piece of hose clamped with Jclps on my shaft just before the shaft leaves the hull in case the prop becomes loose to prevent the shaft droppimg out ( not hapened in 15 years BTW) Not much faith in locktite in this situation - but no harm - belt and bracers!

 

[boatbuilder]

Cobalt drills are what you want for stainless, cutting compound, medium speed and pressure.

 

[bendyone]

When I fitted the engine I drilled through the coupling and shaft and fitter a M6 bolt. Belt and braces!

 

[jax]

I agree your solution is stronger but if your prop gets entangled with something or other between its self and the P bracket - you've lost power, possibly wrecked the prop or
the P bracket or even changed the line up of shaft and engine With our solution you have also lost power, but after clearing the prop you only have to re-tighten the shaft -- Not so ?
Regards Jax

 

[Aeolus_IV]

I also had a keyway cut into the shaft and coupling to prevent this happening, as it looked like the shaft was starting to slip/spin. There was only so much torque I could put into the bolts pulling the clamp together. Its been fine ever since. I am not sure that you should "plan" for the coupling to slip when something unexpected happens, otherwise there would be a recognised "proper" way of allowing for this eventuality.

2p,
Jeff.