How is prop shaft attached to gearbox?

[davidbfox]

Old Snapdragon 747 with Yanmar YSM12 engine.

Now my engine is rebuilt and running clean I've got round to cleaning up my oil stained bilge.

On cleaning I found I may have a problem with the propellor shaft attachment to gearbox flange.

The shaft is clamped between two 'u' shaped pieces, which are bolted to the flange plate that connects the shaft to the gearbox. Now it is cleaned up I can see this:
- on the 'u' clamps around the shaft it looks as if there should be a pair of bolts holding the u pieces together and clamping the shaft.
- there is only one bolt, with no nut on the end.
- the bolt is much shinier than anything else and looks like a relatively recent addition
- where I would expect a second bolt to be, there is a hole both sides but something prevents me passing anything though (i.e. the hole is blocked when probing it with a screwdriver); maybe there is some sort of recessed grub screw arrangement?
- the holes appear to be threaded but none of my bolts would fit (maybe it's not metric?).
- everything appears tight and the shaft turns as it should

As I did not have glasses, camera or a bright light I haven't got any further today.

My gut fear is that prop shaft is about to fall off - not a pleasant thought.

So to my question:
- are there usually a pair of bolts?
- are the u pieces threaded?
- is there any sort of recessed grub screw arrangement?

Engine was rebuilt in situ so shaft and gearbox have not been disturbed by me. Sorry - no photos available. Thanks in advance for any advice.

 

[WindermereColvic]

Cant help solve your problem, but you could add a shaft anode or a big jubilee clip on the the inside end of the shaft, so if it does give way, it wont be lost out the back of the boat.
As an aside, how on earth are you getting behind the engine on a 747?? We recruited a very thin child to change the gear box oil when we had a 747, never mind getting as far back as the shaft. (Don't worry he was suitable remunerated with icecream)
Matt

 

[MoodySabre]

They are all a bit different. Below is picture of mine. You will see that there are 3 bolts from each side (threaded not nuts) and a grub screw. Not all have grub screws - some have roll pins, some have keyways, some rely on doing up the bolts.

 

[colvic987]

some pictures should give us a better clue to your shaft arrangement, as there are various ways of attaching the gearbox flange to propshaft, volvo flexible coupling, r and d coupling, bullflex, centaflex, and many more..

 

[Polly]

They are all a bit different. Below is picture of mine. You will see that there are 3 bolts from each side (threaded not nuts) and a grub screw. Not all have grub screws - some have roll pins, some have keyways, some rely on doing up the bolts.

Can you tell me how you managed to get to the propshaft in your picture?

I'm considering buying a Snapdragon 747 but apparent lack of access to the rear of the engine, propshaft, and exhaust outlet (let alone the rudder tube) is worrying me.

Your knowledge would be appreciated.

 

[vyv_cox]

The type of clamp you describe has the holes (or maybe only one of them) between halves slightly offset so that the bolt would pass right through the periphery of the shaft. This requires that a circular section recess be machined in the shaft to allow the bolt to pass through. This then prevents the shaft from coming out of the coupling and provides a positive stop to rotation.

I would remove the existing bolt to see whether it goes straight to the other half, or via such a groove in the shaft. If there is no groove it is possible to file one with a round file if you are patient enough.

 

[Stemar]

Can you tell me how you managed to get to the propshaft in your picture?

I'm considering buying a Snapdragon 747 but apparent lack of access to the rear of the engine, propshaft, and exhaust outlet (let alone the rudder tube) is worrying me.

Your knowledge would be appreciated.

I wouldn't let that put you off. I doubt it's much worse than most boats of that size and price range, and the boats are pretty roomy for their size and tough as old boots. OK they aren't going to win many races to windward but, with a clean bum they can surprise plenty of so-called quicker boats off the wind.

I have a Snappie 24, which is an earlier model. While things may be a bit different, I'd be surprised if they're that different. Access to all behind the engine requires lying on the engine, but isn't actually that difficult, but I would recommend a lump of foam or an old pillow, 'cos bits of engine get in all sorts of uncomfortable places! I've currently got bits of stuffing gland & coupling spread across my workshop, so it isn't that bad.

Access to the rudder tube involved sliding between the engine and the underside of the "bridge deck". This requires a degree of nimbleness that is problematic for a fat old fart like me, so bribing a more svelte assistant may be necessary. I was able to do it a few years ago when I replaced the badly corroded copper tube with a piece of wind surfer mast, but chickened out and got a mate to go in to fix a fuel leak a couple of months ago!

 

[NickRobinson]

747??

Cant help solve your problem, but you could add a shaft anode or a big jubilee clip on the the inside end of the shaft, so if it does give way, it wont be lost out the back of the boat.
As an aside, how on earth are you getting behind the engine on a 747?? We recruited a very thin child to change the gear box oil when we had a 747, never mind getting as far back as the shaft. (Don't worry he was suitable remunerated with icecream)
Matt

Tell Qantas, they need some help with that RR engine, bit hard on sprog though....

Moving on-

Was your YSM leaking from the gearbox output shaft seal like mine is? If so I'd like to ask how you did the job.

Nick