Engine/Shaft alignment.

N

Nasher

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Down South near Pompey
www.simonnash.co.uk
Hi all.

Does anyone have any tips for aligning an inboard engine with a shaft?

It’s all very small, and space is tight. The shaft is only 5/8in, the same as the engine output shaft, and the engine a small 4.5HP twin cylinder 2-stroke with a flat mounting plate that has four holes for feet.

I have yet to fabricate or source a flexible drive coupling, and the engine will need some rubber feet between it’s mounting plate and the bearers to reduce vibration and noise through the boat.

Before I start on the coupling, is there anything I can design in that would make my life easier when trying to align the engine and shaft?

One last thought, considering the low power and torque output of the engine driving an @8x7 prop, and that I’d align it as best I could, would it be possible that something as simple as a length of thick wall rubber hose clamped to join both shafts would be sufficient?
Or am I just being daft?

Thanks

Nasher.
 
I assume you've got, or will have, engine mountings that are adjustable for height and have enough flexibility to allow a few degrees of twist, vertically and horizontally. Presumably, you also have a drive plate on the engine and a matching plate on the shaft. If so, separate them and offer them up to each other. Alignment is the "simple" process of adjusting the height of each engine mount so the plates touch all the way round. It isn't difficult, but is time-consuming and probably best not done when there are persons of a sensitive disposition in earshot.

When I bought Jissel, she had a 7hp engine and the flexible coupling was a pair of plates, one mounted to the output of the engine and the other to the prop shaft and 5 or 6 gizmos a bit like this: http://www.vibrationmounts.com/RFQ/VM01018.htm bolted between them. It worked fine for the 7HP, but got very upset when I re-engined with 28hp!

Thick-walled pipe as you suggest is, of course a daft idea, but if you can get something heavy enough, it might just be daft enough to work. If you can find it small enough, something like the stuff they use to mount stuffing glands should work. If not, I'd be tempted to try the heaviest pipe you can find with a couple of heavy-duty jubilee clips on each end (put the adjusters opposite each other for balance), and run it tied to a pontoon. The worst that could happen is that it will fail or slip and, alongside, that's not a catastrophe. If it lasts for a couple of hours of flat out, going from ahead to astern as quickly as you and the gearbox are comfortable with with no apparent damage, I'd say you're on to a winner.

At the risk of giving egg-sucking lessons, I think I'd regard it as a service item, examining it regularly and changing as soon as there's any sign of deterioration. I't also carry a couple of spares because even if it's adequate in normal use, a rope round the prop could well snap it.
 
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davidej said:
Check whether, if the hose came off the shaft, could the shaft drop right out through the end.

if so, that is a disaster waiting to happen and must have something to keep it in position.
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Absolutely, but that something could be as simple as a couple of jubilee clips or, if it's a reasonably firm fit on the shaft, a centimetre of your pipe pushed down towards the shaft gland.
 
If its a small engine and the mounts are new - and you 'can' get it a nice face fit at the flange, you may well not need a flexi coupling at all. The simplest is what I have on a 1gm10 - R&D from asap - http://www.asap-supplies.com/marine/r-and-d-marine-flexible-shaft-couplings

To get alignment initially in the right ball park takes a little ingenuity/planning ie 'thought' ! Mount sizes, angle, adjustment range etc. Whether the engine is going to foul anything - not easy really.

Once set in - with the boat on the water - adjust things so the two flanges are sweet on a feeler gauge all round.
Try it without - if its shaking and vibrating - then fit a flexi . I doubt you would have to alter the shaft length. Depends on your set up.

I have know folks not to have one - mostly when the prop shaft is a short run ( canal boat etc )

Geoff - lena, Uphill, Weston s Mare.
 
Thanks guys, interesting thoughts.

Unfortunately I don't really have much room in there for a large diameter coupling, about 3in max, which limits my options, and was why I was going to machine something myself. Three of the small bobbin type mounts might work Stemar, thanks for that idea.

It's a small craft I'm restoring and there is no fwd/rev gearbox or even clutch in the craft, it wasn't designed with one in mind, the engine is permanently connected to the prop.
I do want a flexible coupling, mainly as the craft is of aluminium riveted construction and I'll need to isolate the engine from the bearers on some sort of rubber mount to keep the vibration and noise down. To my mind that means I have to have a flexible coupling to the shaft as well.

I am also still looking for a shaft seal/stuffing box, but it's so small I think I'm going to have to machine that from scratch as well.

Nasher
 
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Flexible mounting feet are easily sourced from lots of places they will make everything easier as they are easy to adjust for alignment. Oterwise you would need to use blocks of vulcanised rubber or HMWPE and steel shims.
If you cannot buy a flexible coupling to suit then you could go down the route of machining one. Steam turbines used to be coupled by means of what was effectively a splined collar on each shaft which fitted into an internally splined tube which was free to float. this gives a slight amount of flexibility. However it will not transfer thrust and you should remember that it is the thrust block that actually drives the vessel forward. If using the above type of coupling you would need to have a thrust block/bearing on the prop side of the coupling.
 
Shaft seal - and outer cutlass bearing ( ie the bit through the hull ) are just screwed onto either end of the stern tube - so the assembly can be very short if needed.
See T Norris website - they have all the options well illustrated. If you have as stern gear problem they are the people to talk to. Old fashioned firm - very helpful !

Have fun - you need a bit when dealing with stern tubes !

Geoff
 
Basic rule is you can have any two of the following flexible
Mounts coupling stern gland
One has to be solid.
The coupling has to transfer thrust both ahead and astern so this may be best to keep solid
Trellberg? May be source for engine mounts and someone may still have Stuart 5/8 strenglands
 
What are the distances from coupling to stern gland and stern gland to bearing, and any other bearings if you have them such as a P bracket. Shafts are flexible.
 
Thanks for all the replies guys.
I think I need to take some pictures to show you all what I'm up to, but won't be home during daylight until Saturday.

One thing I should point out is that there is no fwd/rev gearbox or clutch, the engine is always connected to the shaft/prop and if it's running the prop is turning.

It's a historic boat with a few sketchy details available.
I have the correct engine, and being a riveted aluminium construction the bolt holes for the engine mounts are in a set position.
There is very little room between the end of the engine output shaft and the sterntube, @6in.

Nasher.
 
I think you may find it difficult or even impossible to get jubilee clips tight enough to grip the shaft. There are other types of clip usually with a bolt for applying much higher pressure. Even so you might still have problems with it slipping.
 
oldharry said:
I think you may find it difficult or even impossible to get jubilee clips tight enough to grip the shaft. There are other types of clip usually with a bolt for applying much higher pressure. Even so you might still have problems with it slipping.
Click to expand...

If you are keen on this low tech approach increase the diameter of the shafts with ally sleeves (38 or 50mm ) grubscrewed to the shaft,knurl the OD to increase grip & use hydraulic hose,a nice smile at Pirtek may get you a suitable offcut of pipe from the scrap bin.


Jim
 
What about a cheap laser pointer. Making a bush to fit will be easy enough and the drill a hole for a tight fit. I'm sure I saw a cheap pointer on E bay a while ago
 
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