Engine allignment etc

[jmp]

Have heard it is important to equalise weight on mountings.I assume this relates to fore and aft pairs as the gearbox end is usually heavier.The aim is to have similar compression on the mountings each side in an effort to balance the motion .
The practice is I beleive especially effective with the Vetus hydrostatic mountings and single and three cylinder engines

Does anyone know how this is achieved ? I have thought for sometime ,but am not sure I have solved the mystery.

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[AndrewB]

Not possible, surely.

Can't say I've ever heard of this requirement, though it is important that all mounts are rated to take the actual weight on them.

Given the engine must be fixed in relation to the shaft and also must be set up upright, the only possible way you could achieve this is by moving the mounting bearers in and out. In other words the bearer would be closer in to the shaft axis of the engine on the 'light' side and further out on the 'heavy' side. This is rarely, if ever practicable.

 

[Birdseye]

dont think what you have been told is correct. the weight on front and rear mountings is unlikely ever to be equal, and engine mounts are usually different front to rear.

talk to one of the engine mout makers to confirm what is correct for your engine

key thing is to concentrate on alignment which benefits from being as close as you can get it - certainly to a thou or so.

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[Avocet]

As has already been said, there's nothing you can do other than move the engine mountings so that the centre of gravity of the complete engine/gearbox/coupling assembly is equidistant from each mounting. This will probably mean having the rear ones a long way behind the back of the gearbox. Remember that as soon as you apply any power, the load on the mountings on one side will increase and the load on the two on the other side will decrease - so when you're running, they won't have the same loads on them as when you're stationary anyway! Worse still, on some installations, they will also have to cope with a "shear" load as they take the thrust from thew propeller as well!

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[jmp]

Re: Engine allignment etc,AndrewB ,birdseye &Avocet

Thanks for your replies.
Interesting however the procedure was related to me by a well respected Vetus dealer,who said he supplied instructions with mounts he sold .Unfortunately I did not need new mounts.
He said the procedure was too lengthy to explain over the phone!
I see now my own torment was justifiable,and perhaps I am not as thick as I thought in not easily understanding the idea.

Thanks again

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[Plum]

Having recently replaced my Vetus hydraulic engine mounts and also been involved with designing engine mountings for road vehicles, I have to say that there is SOME truth in the advice you were given. Each rubber mount of an engine should be designed for a given frequency range and loading for optimal isolation of vibrations. However, in reality there is a wide tollerance of loading for a given mount. Although the load on each of the four mounts on the 3-cylinder Vetus engine are different, Vetus specify the same rubber mount for each corner as I expect the load differences are within the acceptable limits of each mount. However, if the verticle adjustment on each mount was such that, say, the front right hand and the rear left hand ones were taking most of the load, then you could have a situation where at least one mount was taking a load outside of the tollerence which will mean that it cannot isolate the vibrations correctly leading to fatigue (of the components, not just of you).

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[jfkal]

Might well be that the front is heavier. In any case the engine suppliers will give you the right mounts (ie Yanmar) has different mount for front and aft taking care of that problem.

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[colvic]

Re: Not possible, surely.

Why are we always hell bent on making things as difficult or complicated as possible? Check the engine manufacturer web sites and those of mounting manufacturers and all will end up saying the same: alignment and mountings sized as per weight of the engine.

One other point, if it is so difficult in a boat, then why are the engine mounts in a car so simple in comparison? They are also a lot less substantial and IMHO the whole configuration in a motor car will take a lot more strain than that in your "average" boat.


Phil

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[stubate]

good on yer

your right, some people scrutinise things so much that they end up looking up their arse!!
i am convinced that the osmosis argument has come about because of this.
reminds me of the last day of the flotilla in greece, man was amazed that i went top side of him and left him for dust, told him, tongue in cheek, that i had keel hauled the boat with a towel, the polish was enough to give me the edge, left him working out how to rig the lines around the hull!!
stu

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