Jump to content

Propeller shaft flexible coupling 'broken? ?


Featured Posts

Hello you wonderful people, much appreciated your help last summer with a fuel issue.

 

Today, I lost propulsion and thought it was the throttle cable, however I found that the cable was working fine and the prop shaft was turning just fine out of the engine, but the other side of the flexible shaft coupling was not turning.

 

I have no idea how a thrust plate works, so would appreciate any primer to help me understand what has gone wrong, and what I need to do to fix it.

 

Many thanks 🙏 

20230202_140617_exported_1716815338845.jpg

Edited by moiuk
Link to comment
Share on other sites

  • moiuk changed the title to Propeller flexible shaft coupling 'broken? ?
Just now, mrsmelly said:

Do you mean that the shaft is turning at the back of the gearbox but beyond the cush drive donut jobby it's stood still??

 

Correct..

 

It is turning very slowly as there is some transference of the shaft turning, but not anything of significance.

Link to comment
Share on other sites

  • moiuk changed the title to Propeller shaft flexible coupling 'broken? ?

I am not familiar with that unit. It could be a simple matter of tightening the unit to either end of the shaft or it may be sheared at some point. More close up piccies may help. Someone like Tony will be along in a minute.

Link to comment
Share on other sites

Its a Fenner split tyre coupling.  The tyre looks OK from your photo.

The coupling has 2 tapered locking bushes inside which are on the 2 parts of the shaft. These may have become unlocked allowing the shaft to turn but not drive the tyre.

To dismantle you remove all the bolts and it falls apart.

  • Greenie 2
Link to comment
Share on other sites

7 minutes ago, Tracy D'arth said:

Its a Fenner split tyre coupling.  The tyre looks OK from your photo.

The coupling has 2 tapered locking bushes inside which are on the 2 parts of the shaft. These may have become unlocked allowing the shaft to turn but not drive the tyre.

To dismantle you remove all the bolts and it falls apart.

 

Falls apart sounds dramatic 😔.

 

Any danger/risk to me removing all the bolts and checking the bushes?

 

Thanks Tracy.

Link to comment
Share on other sites

No, there are no springs or traps!  The drawing on the post before will help you understand how it works. The input shaft has a taper bush attached which locks by the taper into one side. The output shaft is similar locked into the other side.

The tyre fits in grooves in both sides and transmits the drive.

So a loose tyre or either taper bush loose on the requisite shaft or loose in the tyre will stop it driving. They are normally very dependable but don't like getting oily.

Fenner still make these I believe.

  • Greenie 3
Link to comment
Share on other sites

Very helpful.

 

I'll take it apart tomorrow.

 

I did have a bulge issue a while back and the shaft got submerged in oily bulge water so that probably didn't help if it doesn't like getting oily...

Link to comment
Share on other sites

2 hours ago, moiuk said:

 

Falls apart sounds dramatic 😔.

 

Any danger/risk to me removing all the bolts and checking the bushes?

 

Thanks Tracy.

Is the shaft out of the gearbox is turning as normal?   

Is the metal disk between the tyre and the gearbox turning as normal?

Is the tyre turning as normal?

Is the metal disc on the back of the tyre turning as normal?

 

It could be as simple as the tyre slipping in the metal disc depending where you answer no to the above questions, I have the same coupling on my boat

Edited by ditchcrawler
I like adding bits
Link to comment
Share on other sites

6 hours ago, ditchcrawler said:

Is the shaft out of the gearbox is turning as normal?   

Yes

 

6 hours ago, ditchcrawler said:

Is the metal disk between the tyre and the gearbox turning as normal?

Yes

 

6 hours ago, ditchcrawler said:

Is the tyre turning as normal?

No

 

6 hours ago, ditchcrawler said:

Is the metal disc on the back of the tyre turning as normal?

No

6 hours ago, ditchcrawler said:

 

It could be as simple as the tyre slipping in the metal disc depending where you answer no to the above questions, I have the same coupling on my boat

 

Thanks.

 

I'll take it apart tomorrow and check it.

Link to comment
Share on other sites

The Fenner Rub-O-Flex coupling was discussed on this forum a short time ago.........I found the book on ebay.... "16&1/2 Bishop Lane ....The story of A.C.Fenner Ltd"

Link to comment
Share on other sites

It started slipping for a reason.  Is the prop and it’s shaft up to the donut free to turn, or is the prop fouled, and that is giving a reason for the friction surfaces in the donut to slip over each other?

Link to comment
Share on other sites

i always cut these coupling from the scrap....I love them .....they are a very elegant solution to shaft misalignment ,and unlike jaw types with plastic inserts ,dont detoriate quickly.............they work really well in home made generator sets ,damping the heavy shaft oscillation you sometimes get with gensets that arent close coupled.

Link to comment
Share on other sites

31 minutes ago, cobaltcodd said:

It started slipping for a reason.  Is the prop and it’s shaft up to the donut free to turn, or is the prop fouled, and that is giving a reason for the friction surfaces in the donut to slip over each other?

 

The prop is free to turn freely.

Link to comment
Share on other sites

I pulled one off a motor just recently,and dont recall any locks or keepers on the bolts..............rubber is squashable ,and this will relax the tightness of the bolts over time .....which may allow the coupling to slip ,and also allow bolts to come out.............boats need regular inspection and maintenance to keep them trouble free.

Link to comment
Share on other sites

Posted (edited)

Have taken some close up pictures..

 

Hard to tell without taking it apart or being able to compare with how it should be, but there seems to be loose grub(?) screws and a section of the flange sheared off..

 

Have paused unscrewing it to consider my options, but feels like I need to order a replacement flange to insert into the coupling to grip the shaft?

 

Thoughts?

20240528_161101.jpg

20240528_161054.jpg

20240528_161047.jpg

 

 

 

This seems to be a matching replacement??

 

https://e-rubber.eu/product/complete-shaft-coupling-interchangeable-with-fenner-f70-afm/

 

 

And this is a very helpful installation video that makes it clear my flange has sheared and needs replacing.

Edited by moiuk
Link to comment
Share on other sites

I have the same,

fenur tyre coupling,

 

I can’t saying anything the others haven’t said. 
Make sure all the heads are nice and tight. Do them alternately so they tighten evenly, 

and keep going around and around till good and tight, for they do need to be very tight, 

you’ll find some become loose as the others tighten You will need to go around several times. 
If that ain’t solved it then it could be the tapered bushes that hold the discs (?) on the shafts. 
 

Mind when mine went the coupling was clearly loose and wobbley. 
 

There’s every chance the bolts are just loose. 

If you’d sheared any bolts they’d be laying in the bilge, 

 

argh, yes, I see it now there’s a bit of the tapered bush missing by the grub screw?

 

if it is that, it’s an easy and cheap thing to fix,

got mine from ASAP spares, was less than £20 

 

dismantle it all to find out,

knowing how to change that coupling is a good thing to learn anyway

 

 

Link to comment
Share on other sites

Thanks Glen.

I can't find a replacement flange on ASAP Supplies.

 

There seem to be a few different types of flanges, I think mine is a F70 type H (at least that matches the pictures best)..

 

Best match I have found so far is at https://shop.eriks.co.uk/en/fenaflex-f70-type-h-flange-taper-bore-1610-f70h-fen/ for £60.

 

I will take it apart next and be sure I have the correct matching replacement type.

 

Link to comment
Share on other sites

Hang on,

 

I think you’ll need one of these;

 

https://uk.rs-online.com/web/c/mechanical-power-transmission/bushes-collars/taper-lock-bushes/

It’s a very clever bit of engineering, as you tighten the grub screws the taper grips the flange and the shaft and there’s a small locking key involved too. 
 

don't order owt til you’ve took it all apart,

it’s all very easy if a bit of a faff first time around

  • Greenie 1
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.