Vetus type6 flexible shaft coupling

[Wayfarer111]

Anyone with one of these?...no response from Vetus as yet!!

Recently, with my boat on the hardstand I removed the shaft and flexible coupling (type 6) shown below. There were some worrying concerns that will need to be addressed before I can re-assemble; I’m hoping that someone can answer the following questions.

1. The conical clamping hub retaining pins (shown as “A” and “B” below) had broken inside the hub. They may have been the wrong pins? ……what exactly should be used for this purpose?

2. One of the 4 clamping bolts that hold the “clams” together had worked it’s way loose, despite having a nylon locking nut …….when tightening these nuts, what tension should be applied as with a lot of tension the 2 “clams” clamp together which I think defeats the purpose of the rubber “flexible” inserts. Do these nuts need to be tensioned to a specific tension to allow flexibility in the coupling?

3. The rubber inserts could be getting old and worn I suspect as the flexible coupling was purchased by the boats previous owner some time ago ……would it be prudent to replace these?

Any help much appreciated,
Regards, Scott

[stormalong]

Scott, I answered your PM and thought it best to post here as well for others that might have the same quetsions:

I did not use that pin, I thought it was inadequate for the job. I dimpled the shaft, drilled and tapped a hole in the casting and locked the shaft with a hardened steel screw. I cut the screw length down so that it would fit when the coupling is assembled and cut a slot in the screw for a large screwdriver. IMO, the key to preventing the shaft from slipping is to properly clamp that ring that compresses the four fingers of the casting onto the shaft. I made an aluminum plate to fit the notches in that threading ring so that I could torque it with a large monkey wrench.

I really can't say how much torque I use on the bolts that screw to the transmission output hub. My hub (Hurth/ZF transmission) is threaded so no nuts are used. I use grade 8 cap screws - the strongest generally available. I just torque it 'til I feel it is right.

When I assemble it I use anti seize compound between the shaft and the casting. I also spray the rest of the casting with Boeshield T9 to prevent rust.

The rubber pieces should be available from Vetus. I bought a set when I bought the coupling but still have not used them. I have been using this coupling for quite a while now, not sure how long, maybe fifteen years. I take it apart every few years to inspect it and it's still good.

I hope this helps you. If I cans answer any more of your question please feel free to PM me or post them here.

[Wayfarer111]

Just to finish this thread....

thanks Stormalong for the input, i now have a good idea of my mistakes in assembly and understanding of how the coupling works. seems that the cone tensioning collar came loose putting a lot of stress on the retaining pin causing it to break. good thing i hadn't motored too much more before lifting out

Ps. Vetus did also eventually respond today and confirmed your thinking.

[I][I]"These pins are only designed as a safety measure to prevent the shaft from pulling out of the coupling when in reverse if the clamping system fails , as there are broken I would suggest the clamping force onto the shaft has come loose enabling the drive to be taken through the pins"

and,

"There is no recommended torque on the through bolts that hold the outer housings together and attach the unit to the gearbox output flange , these are usually done up tight and don’t usually come loose unless they haven’t been tightened enough or checked after a few hours running . Between the Cross piece [holds the rubber elements] and the outside housings there is no mechanical contact other than the rubber elements . This allows the shaft to drive from the gearbox , through the outer housing , onto the rubber elements and inti the shaft so any vibration is taken up through the rubber elements."

[tkeithlu]

Not quite finished, Scott. Stormalong has a feel for torque that comes from years of experience with a wide variety of bolts. You can develop that feel, too, but until then, a torque table is a great guide to fall back upon. Different size bolts have different nominal torques assigned to them that will hold securely without striping the threads. Here's an example of such a table; they are widely available on the internet. Yes, there are special situations (torquing the bolts on an airplane's propeller comes to mind), but in the general case, torque is applied independent of nylon nuts and Locktite. It does vary with the quality of the bolt, since better bolts can sustain higher torques. Good luck learning your own feel for the situation.

https://www.dultmeier.com/technical-...rque-chart.php