engine alignment

[Guest]

We had a Sole 17hp engine fitted into our 26 foot snapdragon three years ago. Ever since then, the stern gland has leaked, despite being replaced twice by a qualified marine mechanic. It has been suggested that the engine is not aligned properly. Does anyone know how we can check the alignment? (the mechanic says that it is aligned - but he appears to have only checked this by line of sight). And/or can anyone tell us how to align the engine?
The stern tube is now encased in a wooden block which is fibreglassed into the stern and stabalised with resin. It is lubricated by sea water and therefore doesn't have any grease.

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[oldharry]

Checking alignment is done with the boat afloat to avoid distortion of the hull. Slacken off the 4 nuts that hold the coupling between the gearbox and the prop shaft. Ease the shaft back so that it is clear of the gearbox coupling, then push it back into position so that the faces of the flanges meet. Check firstly that the shaft is not offset from the gearbox , i.e. that the centreline of the prop shaft lines up with the centre line of the gearbox output shaft. Usually the flanges will be machined to precisely the same diameter, so that it is a matter of just feeling to see if there is a step between one and rim and the other.

If all is well, use a feeler gauge and check that the gap between the flange faces is the same all round. If it is wider one side than the other, then the centre line of the gearbox output shaft is lying at an angle to the prop shaft, and this must be corrected.

If the engine is not correctly aligned (and it cannot be done by eye - it must be measured as above) then the engine mounting bolts are released and thin metal plates usually around .5mm thickness, and cut square with a slot to the middle for the mounting bolt are inserted or removed between the engine mounts and the engine bed to raise or lower the angle of the engine until two flanges are as exactly in line with each other as you can get them.

It sounds complicated, but actually is pretty straightforward, needing a bit of perseverance to get it right. When the engine is in line with the shaft, tighten the bearer bolts back down, then recheck the alignment at the flange before tightening that back down as well. Sometimes tightening the engine bearers down pulls it back out of alignment, in which case, stop and have a cuppa, then start all over again!

However, before starting all this, check that the stern gland itself is OK. If it is a conventional stuffing box, is the packing OK? Has it been greased regularly with the correct grade of grease? Try tightening the ring nut down to the point where it is just not possible to turn the shaft by hand, then back around 1/8th of a turn so that the shaft is free.

Good luck!


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[Talbot]

why not get one of those thingys that are designed to solve any misalignment problems I think its called an aquadrive.

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[LadyInBed]

Re: flexible coupling

A flexible coupling will sort out any minor misalignment or vibration problems.
How old is your prop shaft? They ware as well, and can cause leaks. If you haven't got a flexible coupling, fitting one will also move the prop shaft back about 3 inches or so (if you have the room to do it) and move the ware point on the shaft a bit further back down the tube.


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[vyv_cox]

In addition to the points correctly made by Oldharry, it is possible for the engine and shaft to be in perfect alignment with each other but not with the boat. If, for example, the P-bracket is not central, the shaft could be running at an angle within the stern tube, which will definitely lead to stern gland leakage. Same thing will happen if the engine is offset to one side but the P-bracket is central. So check that the shaft is central in the tube, both horizontally and vertically.

Don't even think about an Aquadrive until you are certain that it's the only answer. It is an expensive solution that may not solve your problem.

If your 'qualified marine mechanic' has been the same one each time, I suggest you try another.

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[Guest]

Thanks for your help! We have indeed decided never to use our 'qualified marine mechanic' again!

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