Engine Alignment

[jimi]

I'm getting a bit of vibration off the engine when in gear. Engine is a Yanmar 3GM, is realigning it something that I an engineering imbecile is capable of, or should I get a wee man in?

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[Jules]

I did my 2GM last year. As long as you can get at all 4 mounts easily it is simple enough to do. Don't forget you are moving about the centre point of the engine, so if you want to raise the gearbox, say, raise all 4 equally to start. Does take a long time and thus if you pay someone it could be costly.
After I did mine the local Yanmar man told me I shouldn't have bothered as the mounts are very soft and the engine sort of 'floats' at revs, and self aligns as long as it's not too far out.
Oh, and regarding hull shape do it in the water, with the backstay adjusted as in normal motoring if this is an option. I once sailed on a racer whose cupboards wouldn't open or close with the backstay on!
Apart from the obvious reasons such as bent shaft or bad prop make sure the engine is injecting equally into all 3 cylinders. You should be able to put your hand comfortably on the rocker cover at full revs in neutral.
Cheers
Julian

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[tillergirl]

That's a tricky question. The theory is dead simple assuming you've got flexible mountings. You open the coupling, ease the prop shaft back then assuming your unsupported shaft isn't too long to sag through it's own weight, you adjust the nuts on the flexible feet after slacking off the lock nut on top.

What I find difficult is which nut to turn cos you've got to get it right for height, angle (up and down) and straight (down the centre line of the prop shaft). Multiple angles always did confuse me. And it assumes that you can free up all the nuts. Must check mine this winter.

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[MeritaII]

Hi,
You can line up your shaft and engine without too much problem, first make sure that all the assorted nuts are free but not slack.

Undo all the nuts on the coupling except for one this you slacken untill you can just get a feeler gauge in between the two flangesabout 25thou should do it , we used to use the cardboard out of a fag packet ,( but that was before we had thin metal !) so in truth anything that is thin and not too sagy will do .

Put your feeler gauge in between the two flanges and nip it up so you can just pull it out then use the engine mounting nuts to move the engine (and there fore flange) so that you have the same gap on the opposit bolt , now turn the engine by hand and do two more bolts opposit each other, keep doing this untill all the gaps between the flange are the same .
You may have to have two or three goes at it , but take your time, it is a good idea to give everything a little oil or WD40 before you start so that it moves freely, this makes life a little easier
When you are done all the gaps at all the bolts should be the same, now tighten up all the flange bolts and engine mounting bolts and the job should be done. Make sure everything turns freely by hand before you start the engine.
If it isn't then you may have a problem with the shaft , cutlass bearing or the prop.


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[Birdseye]

Can you do it? Of course, you can. Its simply getting engine and shaft in a straight line, and what is required more than anything else is common sense and patience. You are at an advantage compared to hired help, since you dont have to worry quite as much about the time the job takes.

Follow the technical advice already given.

1/ do it with boat in water since boat distorts when launched.
2/ It helps to have one of those flexible couplings that allow you to put feeler guages (and a spacer if required) between bolt heads.
3/ Take it slowly. Be persistant.
4/ measure the gap between bolt heads at 90 degree intervals. Try to get the differences less than 0.025mm. Use feeler guages and a spacer or alternatively, a simple slip guage.
5/ Do the side to side alignment first since that will allow you to bolt down the feet of the engine mounts. Then do the vertical alignment remembering that if the rear legs are twice the distance from the coupling of the forward legs, then the adjustment required is twice as much. eg half turn on the back means quarter turn on the front.



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[longjohnsilver]

Another new discovery Jimi? An engine as well as a holding tank, whatever next? /forums/images/icons/smile.gif

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[Johnjo]

Jimi fouling or damage to the prop can give the same symptoms as misalinement,
might be worth having a look at the prop first.

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[gtmoore]

Assuming that the engine mounts haven't moved and are still in good condition (diesel can wreck them pronto) then I'm with fouled prop idea.

If you do need to align then it's important that the engine doesn't sit at the top of the mount threads by using shims to adjust height as much as poss. Apart from that it's just a fiddly job.

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[jimi]

Did I ever tell you about the time my prop fell off?

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[longjohnsilver]

What! You had a prop as well, shiver me timbers!

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[vyv_cox]

Before you commence a full realignment, and after making sure about the other possibilities mentioned here, such as a fouled prop, I suggest you make sure that the engine is being supported more or less equally on all four mountings. A condition called "soft foot" is a common cause of vibration, where one mounting is less tight than all the others. First, check that all the bolts holding mounting plates to the engine block and the bearers/hull are good and tight. Then slacken off the top nuts on all mountings. Assess whether each mounting plate is pressing more or less equally onto the rubber pad. No rocket science stuff, just waggle the threaded stud and try to get feeler gauges between the plate and the top of the pad. You may even find that a rubber has parted from its bonded plate.

Only after all of this do you need to think about alignement checks. Don't forget that alignment is lateral as well as vertical. You might have to move the engine sideways on its slotted holes, usually where the pad attaches to the bearers or hull. If so, try to ensure that the shaft remains central in the stern tube.

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[Guest]

Don't forget to check cutlass bearing.

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[nicho]

Jim, the latest Sailing Today magazine's test of the Oceanis 331, mentioned the same problem. It was not a brand new boat, but suffered the same vibration. Maybe it's endemic with the model - if so could Beneteau offer advice?

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[AndrewB]

DIY-ing it.

OK, so the concensus is you've got to get your hands dirty.

First time you tackle this, it'll be a long day spent shoving, wrenching and swearing, with oil up to the eyeballs as you stretch round the back of the engine measuring miniscule gaps.

Get the wee man in, a couple of quick shoves and it'll be right within a thou.

So, do it to demonstrate Man's Mastery over Machine. Alternatively, accept Adam Smith's doctrine on the Divison of Labour, and shift a few more units next week (or whatever you do to earn a crust) to support the local economy.

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[TheBoatman]

Re: DIY-ing it.

Two of our club boats have Yanmah 3GM30 engines and they are both prone to vibration at low engine revs. Yanmah engine mounts are notoriously soft (and expensive) and they break flexables like they are going out of fashion. I replaced them with harder and much cheaper R&D mounts, solved the breaking problem but didn't cure the vibration? At 1000/1500 revs it would rattle yer fillings out but at 1600 revs, smooth as the babes backside.

As for DIY go for it, so long as you have 2 sets of feelers, spanners and a bottle of Scotch you should be OK.

Being an engineer by proffession, I would admit I hate flexable couplings and mounts, they are the engine/boat builders answer to quick and easy "near-enough-is good-enough" problem solving. In the past I have been on boats with solid mounts and you could have rested a 50p on the gunwhale, knocking out a sterntube bearing was almost unheard of. Never had surging or hunting when the boats under power. If you think about it with all these floating mounts and flexable couplings when the engine is driving the only thing that makes the boat go forward is the propeller pushing through the flexable and on to the engine mounts, result flexable deflects under load and pushes on mounts, mounts deflect forward and pushes boat. Then mounts retaliate and push back, flexable goes the same way, end result you get this hunting where the boat appears to "rock" backwards and forwards and the engine noise sounds a bit like its going brmm-brmm-brmm-brmm as the load comes on and off the engine.

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[tome]

Jim

Do you have a shaft anode by any chance? If so, what's it like (could it have been disturbed by the recent scrub?). Just a thought!

Tom

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[jimi]

Tom, the vibration is about same as its been for a while, its not excessive but I would like it to be a bit smoother. No, do'nt have a shaft anode, I used to have one but when the prop fell off(!!!) discovered that there was no anode either so surmised that the anode had fallen off first. I then had a "proper" hull anode wired in. I'll check a few things mentioned out.

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[sidon]

Had a similar problem on my Jeanneau.Engine was 5thou out and had slightly worn cutlass bearing, which apparently caused the vibration. Got a man in to align the engine cost 40 quid. Hope this is of help.
Simon

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