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adjusting and aligning an engine and prop shaft


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After the engine removal earlier in the year, SO has developed a distinctive harmonic beat.  Dance-able (kind of a fast, 3/4 time) , but not so conducive to comfortable motoring. 

On inspection when we are in gear and swinging the prop the rear of the gearbox visibly rises and falls about 1.5mm.

It appears that just stuffing her back in with everything bolted exactly where it came from and not adjusted is insufficient for good engine alignment.

Fortunately, the engine mounts are adjustable - I was expecting to have to make shims etc, but the mounts are threaded with castellated nuts on top and a locking nut underneath.  1 1/4 inch, or 32mm in the new money

Apart from the standard wisdom and technique with feeler gauges at the coupling flange, is there anything else I should consider before diving in?

I'm secretly hoping this will help address some stern gland leakage too...

 

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Check for barnacles unbalancing the prop first.

Second make sure the shaft is exactly central in the shaft log (stern tube) first before doing the feeler gauge bit. Perhaps actually put wedges around the shaft to hold it dead centre. That might involve removing the water seal from around the shaft (unless it's a traditional stuffing box) so might have to be done out of water depending on the setup.

Feeler gauges work. If you use an R&D coupling it has a special bolt head for using the feeler gauges on which makes it easier and more accurate. THe rubber coupling also helps absorb minor vibrations.

If all else fails use a python drive (like the CV shafts on a car) and then you don't have to bother with exact alignments and it doesn't matter if the engine bounces around a bit on the rubber mounts.

This becomes way more critical on electric drives - when the motor is silent you notice all the little knocks and vibrations from the shaft which otherwise get drowned out by the noise of the diesel, so the tiniest misalignment becomes annoying. A Python drive is a great solution then.

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the joys of a dripless gland,when i changed glands,undid the nuts holding shaft,shaft slide out easily. fitted new gland and shaft was 2 mm higher than gearbox,friend wiggled shaft and went in to collar tighten down .in water and all was well.doesnt help you out I know.

So when you turn the shaft you see it rise and fall?? To me that wouldnt indicate motor not aliegned but ,hoping not worn shaft tube,slightly bent shaft

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Cheers guys.  I was planning to release the shaft and check for runout, so, yeah.

We antifouled and propspeeded 6 months ago so if it's growth I'll be pissed off.

Pretty sure it's alignment, it's the only thing that makes sense following the engine out job, but we'll see.  There is a rubber coupling on the flange, so that will be absorbing most of the misalignment.

 

 

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it takes bugger all growth on a prop to throw it out,engine smoking a bit can be a give away sign of growth or revs v speed. Prop speed is not a magic bullet. Looked at yrs ago and seeked advice, you still up clevdon river??now water water warming growth increasing,surprising how many revs it takes to throw stuff off prop..

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Oh Yay, engine alignment, one of my favourite subjects... I've spent years chasing vibrations around my engine.

Other things to check are the state of the cutless bearing. If this is worn, the shaft can flog around and could be the source of harmonics.

The other key thing is engine mounts. They are a consumable item and don't last forever. I'm not aware of a test for them, other than basic age and condition. It is the rubber elements that get old and brittle. If they haven't been changed, and the engine needed work, then its a good indication that the mounts need replacing.

You are pissing into the wind trying to adjust alignment or fix vibration if your mounts are stuffed. So verify they are OK or not before trying to get the engine aligned. Remember that the mounts deal with dynamic loads. When the engine is in drive it doesn't sit in the same place as when its off. I would think 1.5 mm movement at the gearbox is normal for any diesel when it is running, i.e. it jumps and moves as the pistons fire. Hence the need for rubber mounts and flexible shaft couplings.

One other thing is the drive damper plate. They do sh*t themselves every now and then. But I doubt that is the problem from what you describe.

So if everything else checks out, it is a case of checking the alignment with the old feeler gauges. Tips for that, mark the gb and shaft flanges with 12, 3, 6 & 9 so you can keep track of which positions you have checked.

It is sh*t loads faster with two people, one on the feel gauge, the other on the spanners. You can tweak a mount and check / see if it is going the right way or not without crawling out / crawling back etc.

It may help to write down every measurement and adjustment you make. It sounds tedious and slow, but it stops you getting mixed up and making things worse. Certainly a good idea while you are starting, to get the hand of it. 

Be aware also, that trying to fix a vibration on an engine is like painting one room of the house. All of a sudden every other room likes like sh*t / you start listening and focusing on every rattle and shake while you are out cruising...

PS, if you want to change your mounts, Trellborg are good mounts, there is a supplier in town I'll have details for somewhere. They do industrial mounts and vibration solutions, so not a 'marine' retailer, and sh*t loads better product.

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Thanks Fish.  I'm going to disconnect the shaft at the flange and check lateral runout.  The cutlass and hanger were fine less than 20 hours running ago so I am confident (but not certain) that those are not the culprits.

The mounts were all "firm/stiff but compliant" when I had the engine out - no oil damage, no cracks or other signs of degrading.

If I could find someone who will put up with my temper when I'm on the wrenches, I'd do the two people thing.  Unfortch, there are still homicide laws in NZ so possibly best not.

Cheers for the contact for new mounts - if it reaches that stage I'll check them out.

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Not yet - project for first week of January.  Got the tools in place, just the motivation to hang upside down in a dank cavern that smells of diesel and fish and adjust settings at 1/2-a -flat of the nut at a time that's missing.

I used to work on Jaguars and other such stuff that put me off dealing with inaccessible, oddly-sized fixings for life.

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3 hours ago, aardvarkash10 said:

Not yet - project for first week of January.  Got the tools in place, just the motivation to hang upside down in a dank cavern that smells of diesel and fish and adjust settings at 1/2-a -flat of the nut at a time that's missing.

I used to work on Jaguars and other such stuff that put me off dealing with inaccessible, oddly-sized fixings for life.

Check prop for barnacles first though. Just incase pads are right and inline.

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2 hours ago, harrytom said:

Check prop for barnacles first though. Just incase pads are right and inline.

Hmmmn, swim in the murky, Ganges-like waters of the Clevedon river, or measure flange run-out and any offset....

Hard to know which is worse actually.

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