Engine alignment with floating stern gland

[contessaman]

I'm still having some difficulty aligning my new engine. Boat presently back in water.

Am I right in saying that with a 'floating' type Volvo rubber shaft seal, the correct and only way to align things is with boat ashore, remove shaft seal and chock propshaft in centre of stern tube and then align the engine to that? Cutlass bearing is brand new.

Everyone at the boatyard sucks their teeth and tuts at me that I should be lining up my engine with the boat in the water but I really don't see how that's possible as I need the shaft seal off and slid clear of the tube so I can chock the shaft in the midpoint.

Hopefully it is just an alignment issue but I am starting to worry about some other aspects of my new installation:

I fitted an R&D coupling but I've read mixed opinions on this with a flexibly mounted engine and a rubber shaft seal. The shaft is only supported by the cutlass bearing at one and and the r&d flexible coupling at the other. Perhaps I would be better off with a solid coupling.

I made up the new engine mounting brackets so that my replacement engine would fit the bearers without modifying them. The new engine uses a 7 degree down angle transmission as did the md21 lump it replaced. However the original and now replicated arrangement does not have all four flexible engine mounts (I've renewed those by the way) in the same plane as the propshaft. I wonder therefore, with the down angle box can the thrust from the propeller act to push the rear of the engine up and throw it all out of alignment?
That said, this wasn't an issue with the previous engine and also since the wobbling was so bad at idle I've yet to apply any real revs to the engine in gear hence its unlikely that things are being pushed out of shape.

Grateful for any thoughts hints and tips

If it makes a difference to your answers
Engine is a 59hp mermaid with a twindisc TMC60a transmission 2:1 swinging a 15x13 three blader. Shaft is 30mm dia and about 3ft long.

 

[Lon nan Gruagach]

I'm still having some difficulty aligning my new engine. Boat presently back in water.

Am I right in saying that with a 'floating' type Volvo rubber shaft seal, the correct and only way to align things is with boat ashore, remove shaft seal and chock propshaft in centre of stern tube and then align the engine to that? Cutlass bearing is brand new.

Nope, not right although that is the easiest way....
You can support the shaft with chocks up from the hull with a vee block on top, you can centre it athwart with a nudge, then all you need to do is reference it to the stern tube.
A block and a rule will do, press the block against the outside of the stern tube and the rule against the block, passing the seal. Then, with callipers you can set the shaft central to the tube.

 

[contessaman]

Nope, not right although that is the easiest way....
You can support the shaft with chocks up from the hull with a vee block on top, you can centre it athwart with a nudge, then all you need to do is reference it to the stern tube.
A block and a rule will do, press the block against the outside of the stern tube and the rule against the block, passing the seal. Then, with callipers you can set the shaft central to the tube.

What and then calculate the midpoint mathematically from known diameters of shaft and tube?

Would be great if I could centralise the shaft in the tube whilst afloat..

However,

The bronze stern tube is glassed into the hull and the little bit that sticks out before the seal clamps on is faired in with gelcoat or something so it will be incredibly tricky to clamp anything parallel to the tube and whatever I do clamp will need to be very rigid to pass the shaft seal and still give an accurate datum against the shaft

Also, getting the shaft central might be possible but surely it won't stay there when you slide it in and out to get it up against the gearbox flange? Leads me to another problem.. Unless I remove the prop, the shaft can't slide in enough to take the r&d coupling out and bring the two metal flanges together...

 

[Plum]

I'm still having some difficulty aligning my new engine. Boat presently back in water.

Am I right in saying that with a 'floating' type Volvo rubber shaft seal, the correct and only way to align things is with boat ashore, remove shaft seal and chock propshaft in centre of stern tube and then align the engine to that? Cutlass bearing is brand new.

Everyone at the boatyard sucks their teeth and tuts at me that I should be lining up my engine with the boat in the water but I really don't see how that's possible as I need the shaft seal off and slid clear of the tube so I can chock the shaft in the midpoint.

Hopefully it is just an alignment issue but I am starting to worry about some other aspects of my new installation:

I fitted an R&D coupling but I've read mixed opinions on this with a flexibly mounted engine and a rubber shaft seal. The shaft is only supported by the cutlass bearing at one and and the r&d flexible coupling at the other. Perhaps I would be better off with a solid coupling.

I made up the new engine mounting brackets so that my replacement engine would fit the bearers without modifying them. The new engine uses a 7 degree down angle transmission as did the md21 lump it replaced. However the original and now replicated arrangement does not have all four flexible engine mounts (I've renewed those by the way) in the same plane as the propshaft. I wonder therefore, with the down angle box can the thrust from the propeller act to push the rear of the engine up and throw it all out of alignment?
That said, this wasn't an issue with the previous engine and also since the wobbling was so bad at idle I've yet to apply any real revs to the engine in gear hence its unlikely that things are being pushed out of shape.

Grateful for any thoughts hints and tips

If it makes a difference to your answers
Engine is a 59hp mermaid with a twindisc TMC60a transmission 2:1 swinging a 15x13 three blader. Shaft is 30mm dia and about 3ft long.

I have a Volvo shaft seal and when i separate the coupling the shaft stays central in the sterntube despite its weight so i do not need to do anything to centralise it. Regarding flex coupling, as you have a {slightly} floating shaft seal you MUST have one designed to provide positive radial alignment otherwise the shaft side of the coupling can tend to whip about. One of the Vetus flex couplings i have used has a removable insert that either restricts or allows radial misalignment. Works well. However, on my engine that has the Volvo seal i have no flex coupling and has been like that from new 17 years ago.

Www.solocoastalsailing.co.uk

 

[vyv_cox]

Not a 'proper' centralising method, but then it is usually not at all critical. If you loosen the seal from the stern tube and slide it forward some water will enter the boat. However, this can easily be stopped or reduced to almost nothing by wrapping a rag around it. You can then feel whether the shaft is close to the tube or not. It is only necessary to ensure that the two do not clash in service, so central by feel is good enough.

 

[scottie]

Check with R&D if you are in any doubt that their coupling is suitable for your installation you will find them user friendly but generally speaking their couplings are an exception to the 2 of 3 rule
You will have a solid coupling already but may require a spacer if you replace the R&D

 

[Neil_Y]

I'm with Vyv on how critical this is, as you also have to consider the weight of the prop and shaft sitting on (probably) a rubber bearing so the shaft isn't in the centre of the shaft bearing and could be running at an angle to the bearing. When you add thrust the shaft centralises in the bearing but then also wants to bend between supports.

 

[vyv_cox]

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