Coupling Query:- wear and tear

Grief · 12-10-2005

Hi Folks.

I have been testing my new motor (Robbe navy compact 3.3:1 geared)
on my propshaft. All in all Everything looks ok. The exception being the coupling, which after a small amount of running is showing a few bulges around the pins on the universal joint. This will make the holes bigger and presumably lead to some vibration.

What do most of you do
1. Use a fixed coupling (no UJ) and make sure every thing is straight.
2. Use a universal joint coupling but dont see any wear and tear
3. Need to replace the UJ coupling on a regular basis?

At the moment I think a straight joint would be less hassle.

If anyone can recomend a good coupling and place to buy it please post as well.

Cheers

Chris

**Bunkerbarge** · 13-10-2005

Chris,

A correctly set up coupling should last for many years as I am sure a great number of forum members will attest to. The bottom line is that you must have one and it must work correctly.

I would not recommend a ridgid link as you will not be able to perfectly align your motor to a point that would guarrantee the bearings are not adversley loaded and your motor will definitely fail prematurely, even if you think that you have it set up perfectly you will not be able to check accurately enough to avoid this.

Have you used a double UV joint coupling or a single one? If you think about it a single one does not allow for the shafts to be parallel yet offset, it only allows for the shafts to be at an angle to each other. My boat has a double UV joint coupling and is not yet showing any signs of undue stress on the coupling bearings.

Your 70mm prop should be turning very slowly and your transmission should last for a very long time so I would try to find out what is going on. Assuming that the motor, gearbox and shaft all turn nice and freely individually I would put an ammeter in line with the motor power supply and see what current is being drawn. Out of the water you should see negligible current but if you have a transmission problem you may well see a noticable current being drawn.

I would do plenty of experimentation at this point to ensure that you have this right. Dealing with this after the decks have been fitted would be a whole differrent ball game and should be avoided at all costs!

Let us know how it goes and well done for noticing this in the first place. You are right to be concerned but also try to evaluate whether you are actually seeing something and your mind is not playing any tricks. Are you sure these bulges have developed in operation and were not there in the first place?

Good luck,

All the best

Grief · 13-10-2005

Thanks Richard.

I think the problem is that the hole on the motor side of the UJ is off centre.
I hadn,t spotted it before. Must be a dud.
I will replace it and try again.

Cheers

Chris

**Bunkerbarge** · 14-10-2005

Yep,

That would do it nicely!!

It won't be the last thing you will have to send back. Wouldn't it be nice if things were checked out before they left the vendors?

Grief · 14-10-2005

It would indeed. I wont be able to pick this up now for another week so I
have lost a bit of time sadly

Regards

Chris