Prop Shaft Coupling Question

CaptainBob

CaptainBob

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www.yacht-forum.co.uk
I've got a Beta engine which clamps onto my prop shaft in a gripping clamp thing. Four bolts, two each side, tighten the clamp over the smooth, 25mm, shaft.

Problem is I have near zero gap between my P bracket and my prop, and was hoping to install a rope cutter. If I pull out the shaft the required 36mm, I'm left with 20mm still inside the clamp, which I'm guessing isn't enough?

Here's a picture showing my clamp type...

yhq13.jpg
 
I always thought you could buy a spacer to make up this sort of distance - bolted to the flange on the gearbox from memory. Speak to R&D who make the coupling or Beta direct - they are usually very helpful.
 
CaptainBob said:
If I pull out the shaft the required 36mm, I'm left with 20mm still inside the clamp, which I'm guessing isn't enough?
Click to expand...

I'd say 20mm is defo not enough, you need the shaft to be located at least as far within the clamp as the rearmost bolt centerline, otherwise the action of the same would be so as to squeeze the shaft out of the clamp.

Hard to tell from the photos, but other posters' suggestions of a spacer between the clamp and gearbox might be viable. Are the nutted threads I can see sticking out from the clamp a part of the gearbox, or are they studs which can they be swapped out for longer ones ? If so then 4 off studs, 36mm longer than the ones fitted, plus a 36mm plate with holes in the right place and you're good to go.

Of course a new shaft might only be one or two hundred quid and possibly cheaper than a bespoke plate. Deep-ends who you know, innit ?

Boo2
 
rope cutter

not sure about other readers but i have not had much success with rope cutters.
Had a rope around my first one and it pulled out the stationary block from the P bracket.
Not sure if it will not re-offend if unfortunate enough to get yet another rope caught.

sorry nothing to do with the question.

bob
 
rope cutter

There are spacers supplied from the rope cutter suppliers.

I have a spurs cutter, the service you get from Harold Hayes is second to none in my opinion.
various makes on the market and if i was to replace mine again i think i would look at the ambassador one which has the serrated teeth.

I believe this bolts onto ur shaft coupling between the coupling and gearbox wich gives you the necesary clearance.

bob
 
robertj said:
not sure about other readers but i have not had much success with rope cutters.
Had a rope around my first one and it pulled out the stationary block from the P bracket.
Not sure if it will not re-offend if unfortunate enough to get yet another rope caught.

sorry nothing to do with the question.

bob
Click to expand...

Happened to me twice. I have bought a Prop protector instead. Anyone want a 1" Stripper minus the fixed block?
 
These type of couplings are bored at the solid end to match your shaft and act as a witness face in order that the coupling will run true, that is the reason why you will need a shaft exstender.
 
I have a spacer for an ambassador rope cutter but it is off a Yanmar 1GM10 engine so not sure it would fit. It is 15mm thick x 100mm diameter with 4 x 10mm holes (55mm between hole centres at 39.5mm radius from spacer centre). Can send photo if required (PM me).

£15 including postage.
 
Last edited:
CaptainBob said:
Problem is I have near zero gap between my P bracket and my prop, and was hoping to install a rope cutter. If I pull out the shaft the required 36mm, I'm left with 20mm still inside the clamp, which I'm guessing isn't enough?
Click to expand...

read the dimensions carefully on www.ropestripper.com

I think you will find your shaft is already too short as there should be a minimum 10mm gap aft of the P bracket to allow water to flow through the cutless and also allow for the fore and aft movement of the whole stern gear as you go in and out of gear. This can be as much as +/- 3mm for a flexibly mounted engine.

Measure the gap you have and add the recommended space depending on which size cutter you want to fit (there are two possibles for your size shaft) and this gives you the amount you need to move the shaft back, and therefore the thickness of the spacer.

Very straightforward if you follow the instructions.
 
Tranona said:
read the dimensions carefully on www.ropestripper.com

I think you will find your shaft is already too short as there should be a minimum 10mm gap aft of the P bracket to allow water to flow through the cutless and also allow for the fore and aft movement of the whole stern gear as you go in and out of gear. This can be as much as +/- 3mm for a flexibly mounted engine.

Measure the gap you have and add the recommended space depending on which size cutter you want to fit (there are two possibles for your size shaft) and this gives you the amount you need to move the shaft back, and therefore the thickness of the spacer.

Very straightforward if you follow the instructions.
Click to expand...

Must be missing something. I did read the instructions and it says I need a 36mm gap between the end of the P bracket and the start of my prop. This is for the AM5. Can't see any mention of the need for a 10mm gap on top of that. Could you tell me where it says that?

I'm looking at this PDF:

http://www.ropestripper.com/documents/fitting-am5-10-15.pdf

Thank you!
 
I've two couplings back to back; mind you my 1GM10 does rather dance about when ticking over. Alternatiely you could have a spacer made up and use longer bolts. It all depends how much longer your shaft needs to be. You might even find a new shaft the correct length the most cost-effective solution.
 
MERRY_MARY said:
If you need a reasonable extension then you might find a bobbin a solution!

See http://www.asap-supplies.com/ and search "bobbin" and it could give you 4", now size does matter!
Click to expand...

Almost certainly the first 4" 'bobbin' will do but you'll then have to shorten the shaft to suit!
It will have suitable male & female register on the ends so concentricity will not be a problem.
 
CaptainBob said:
Must be missing something. I did read the instructions and it says I need a 36mm gap between the end of the P bracket and the start of my prop. This is for the AM5. Can't see any mention of the need for a 10mm gap on top of that. Could you tell me where it says that?

I'm looking at this PDF:

http://www.ropestripper.com/documents/fitting-am5-10-15.pdf

Thank you!
Click to expand...

No. I was making the point that you should already have a 10mm gap, or so, but whoever installed your engine did not do this. You may well find that the front face of the prop has been rubbing on the P bracket as the engine moves forward when you go into gear.

If you look on the product page at shaft strippers you will find that the AM5 is 28 mm thick and the minimum gap is 36mm. Therefore 8 mm minimum exposed shaft. If you go for the AM 10, this is 30mm thick and the gap is 40mm. So the total gap includes the space for water to come out of the cutless bearing

Hope it is clear now. As you say you have zero gap then you need a 35 or 40mm thick spacer.
 
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