prop shaft to coupling

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Pagetslady

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Hi is it essential to have a bolt through the coupling and shaft on my Volvo 2003 there was one but on the new Beta there is no hole in the coupling also should the shaft be hard up against the flexible coupling, i think I remember reading that this can cause noise.
mike
 
No in fact a bolt through the centre of a shaft is bad practice if you must then across the corner as in a cycle pedal is almost as good as a taper pin.
However a pinching screw into the shaft is correct as it stops the shaft moving in the coupling
 
vyv_cox said:
There are many photos and examples of coupling designs on my website under 'sterngear'.
Click to expand...

Hi VYV i have already looked at your site, and there are some with and some without, I have been running without for 2 years I just wondered what others do. there is a small hole drilled in the coupling but just on one side so I was thinking of drilling that out through to the shaft which would put a dimple in the shaft and then tap a thread into the coupling and put a grub screw in to pinch on the shaft.
Mike
 
With lower power outputs it seems that a friction coupling is considered sufficient, e.g. some Bukh couplings have no positive fastening. Some higher powers use six bolts, not four. Next stage up would be a dimple and grub screw as you describe, then an offset bolt that passes through the shaft at a tangent, avoiding the problem that scottie correctly describes. My coupling on Yanmar 3GM30 has grub screw and dimple.
 
IMHO, if there is a well fitted and properly tightened split coupling, then a grub screw isn't going to add anything.
If a slip did occur, the end of the grub-screw will be mangled and hence a PITA to remove.
 
The "soft" coupling is favoured for many low-power installations, because it prevent an expensive noise from the gearbox if you get a bad wrap. You'll find it as standard on all the GM and YM Yanmars.
A through bolt is (usually) a sign of past problems, overcome in a pragmatic (but not better) manner.
 
My coupling Yanmar 4JH has a bolt through the middle of it. This was fitted by the builder (American) in 2001.
What if any are the problems it will cause?
I have had no noticeable problems so far.
Thanks
 
RAP77 said:
My coupling Yanmar 4JH has a bolt through the middle of it. This was fitted by the builder (American) in 2001.
What if any are the problems it will cause?
I have had no noticeable problems so far.
Thanks
Click to expand...

Fatigue is your enemy. Drilling a hole through the shaft creates a massive stress raiser. The fluctuating stress in the shaft as a result of propeller forces can initiate a crack but this is hugely increased if there is any misalignment. Modern machinery practice is that shaft couplings have no keyways or any other section change.
 
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