Engine vibration advice? - Yanmar single/Sabre

[LittleSister]

A friend has had enough of the vibration from his engine, and is thinking of replacing the engine in his boat to overcome this. As his existing engine is reliable and seemingly adequately powerful, this seems to me a perhaps unnecessarily expensive way to address the problem. Can forumites please suggest alternative measures, and estimate the rough probable cost as proportion of the cost of a new engine and fitting?

The engine is a single cylinder Yanmar 12hp. The boat is an early Marcon Sabre 27. He tells me the engine mountings are rigid (i.e. not flexible) and that the thread has gone on one of the mountings, so (as I understand it) the engine is only actually clamped to three of the mountings. We have been briefly on the boat under engine but this was several years ago now, and as far as I can recall we were surprised by how bad the vibration was, even for a single cylinder. I don’t know if the mounting thread had gone at that point. Until now he has not been in a position to think about a new engine.

Without much experience of inboards, I would have guessed that new, flexible engine mounts, and some sort of flexible coupling between the engine and drive shaft would make a world of difference. However, when I looked at Halyard Marine site about Aquadrives, it seems they only do flexible mounts for engines of four cylinders or more. Does that imply that it’s not practicable to flexibly mount a single cylinder engine, or just that Halyard’s particular product or market doesn’t cater for budget boats/engines?

 

[NickRobinson]

Hi

A Yan single on solid mounts must loosen your fillings....

http://www.ybw.com/forums/showthread.php?t=265784

My YSM 8 was fitted with new mounts very economically and quite easy to diy.

There is a simple plastic flex coupling and a solid stuffing box (no rubber tube )

Much better, (ok these things are relative!)

Hope it goes well

Nick

 

[andygc]

However, when I looked at Halyard Marine site about Aquadrives, it seems they only do flexible mounts for engines of four cylinders or more.

You must have misread that - go to the Aquadrive web site

Aquadrive has systems to match boats powered from 5 hp to 2000 hp

Mine was driven by my 1GM10 and is now driven by the Beta that replaced it.

PS, the Aquadrive site has a broken link to the low power version, so try looking here

 

[LittleSister]

Hi

A Yan single on solid mounts must loosen your fillings....

http://www.ybw.com/forums/showthread.php?t=265784

My YSM 8 was fitted with new mounts very economically and quite easy to diy.

There is a simple plastic flex coupling and a solid stuffing box (no rubber tube )

Much better, (ok these things are relative!)

Hope it goes well

Nick

That's helpful. Looks like flexible engine mounts are possible and not expensive.

Can you tell me a bit more about your 'simple plastic flex coupling'?

 

[LittleSister]

However, when I looked at Halyard Marine site about Aquadrives, it seems they only do flexible mounts for engines of four cylinders or more.

You must have misread that - go to the Aquadrive web site

As far as I can see the Aquadrive site says they do flexible mounts, but doesn't provide any details. The Halyard site says "Aquadrive engine mounts are used with engines of four cylinders or more, and our expert staff will rapidly select the correct rubber stiffness for the machinery involved."

Thanks for the link to the Norris price list.

 

[NickRobinson]

That's helpful. Looks like flexible engine mounts are possible and not expensive.

Can you tell me a bit more about your 'simple plastic flex coupling'?

Like these-

http://www.asap-supplies.com/marine/r-and-d-marine-flexible-shaft-couplings

Nick

 

[Spyro]

Previous boat had a YSB8, very reliable but rattled loose everything on the boat. The mounts were replaced when I purchased it. New flexible mounts had to be sourced as the originals were not available. I doubt very much if this engine is sitting on rigid mounts. The only ones I could get had a bigger diameter mounting bolt which meant drilling out the engine feet because of access problems to the engine it had to be removed to do this.

 

[exfinnsailor]

Like these-

http://www.asap-supplies.com/marine/r-and-d-marine-flexible-shaft-couplings

Nick

Think you need to READ the spec on aligned to 0.01 in a boat .....

 

[NickRobinson]

Think you need to READ the spec on aligned to 0.01 in a boat .....

Scary isn't it.

However

I put Magna's engine back in in the Spring and loosely bolted the flange.

I hand rotated the shaft/flange while adjusting the locknuts on the mounts.

Then pinched them when no sideways forces apparent. I confess, no feeler gauges, no dial gauge were harmed in the doing of.

No noises, no odd movements despite a solid stuffing box. Motors nicely.

I accept that going from solid to new flex mounts may need more thought.

Nick
ps- for entertainment, get a price for mounts from Yanmar....

 

[Tranona]

The engine is virtually solid mounted and the prop shaft is rigidly mounted. This set up is well known for vibration. If you are going to put in flexible mounts then you need to isolate the engine from the shaft with a flexible coupling. The most popular type is from R&D www.randdmarine.co.uk who may be able to help with mounts as well. Be aware that putting the coupling in will move the shaft back and if there is more than 15mm or so clearance between the back of the bearing housing and the prop you may need to shorten the shaft to reduce the overhang - particularly if it is a bronze shaft, which it may well be.

BTW an Aquadrive as suggested would require major modifications and there is probably not enough room anyway. Overkill for this installation. Better to spend the money on a nice new Nanni (or Beta) 16 which will be a huge improvement - but at a cost not far off 50% of the value of the boat!

 

[srp]

I think there's a bit of confusion here between Aquadrive engine mounts and Aquadrive shaft couplings!
Anyway, the best solution is to mount the engine on suitably sized flexible mounts (eg from ASAP, Norris, Lancing Marine etc), and to fit an Aquadrive shaft coupling. But the shaft coupling is expensive and needs about 235mm distance between the g/box coupling and the end of the shaft, which may be totally impractical, and you'd also need to fabricate a thrust plate to bond to the hull.

A cheaper alternative is, as suggested by Tranona, flexible mounts and an R and D coupling. You will also need a stern gland which will allow some lateral movement of the prop shaft within the shaft tube. If you have the room then 2 R and D couplings with a 'bobbin' shaped coupling in between them will be even better (I think this is mentioned on the R and D site somewhere).

And, as Tranona hints at, a 2 cylinder engine will always be smoother than a single.

There is some excellent information on Vyv Cox's web site on stern gear installations of all types - well worth reading before you spend any money.