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post #1 of 7 Old 05-29-2011 Thread Starter
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Engine mounts

Hey guys,
my rear engine mounts (yanmar 12SB), Ontario 28... seem to be quite high, one top stud is recesed in the bolt. and the opposite (front left) the rubber is degraded probably due to oil drips...

should I can I tighten them, would that change the pitch too much for the stuffing box etc...

also, what are your thought s on removing the engine, changing the rubber mount and repairing anything else under there ( the muffler is loose on its mount too..... all while in the water ??? or should I wait util the fall ?

Any help appreciated.

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post #2 of 7 Old 05-29-2011
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you can try tightening them but usually they are too rusty after you will need to realign the engine,use feeler gadges beween the couplings,i think you can also put on new ones by unbolting the coupling then jack up the engine,you my need to unbolt the brackets that the mount studs go through,hard but doable,the muffler can maybe be tightened by using slightly larger screws
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post #3 of 7 Old 05-29-2011
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Nothing should be adjusted without redoing/rechecking the alignment too. It sounds like a couple of mounts are in rough shape and should be renewed.

If you have a conventional stuffing box then removing the engine and tranny in the water is no big deal, esp if you're able to use the boom and tackle as a hoist. We've done it a couple of times.

If you have a dripless (PSS) style seal than you need to worry about that - once the engine and gear are removed there's no pressure on the seal and bellows anymore....

It does sound like a Re & Re might not be a bad idea, you could tend to these issues, give the works a good clean up, and maybe change some seals and gaskets while you're at it.


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post #4 of 7 Old 05-29-2011
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From what you say it looks like when your engine was last installed the mount feet weren’t properly shimmed. Basically the engine should ride in the middle or lower part of the stud that comes off the mount. If, to align it, the engine is on the top of the mount’s stud you put some material under the feet of the mount to raise it up so the engine rides lower on the stud.
If you’re engine is running smoothly there’s no urgency to correcting this. Give it’s the beginning of the summer I’d wait. You never know what rats will crawl out of the woodpile when you start taking your engine apart.
I’d be concerned about and fix the exhaust system issue . The exhaust hoses should take up the vibration and the mounts should be secure. A hose failure and the leaking of CO and water into the boat is a big problem.
It’s not too likely that the other mount is too low because of degraded rubber. It’s probably low because that’s where it had to be on the stud to align the engine to the shaft. The engine lets you know when the mount’s rubber deteriorates to the point they need to be replaced. Usually mounts only get changed out when doing a major engine overhaul or replacement. They just don’t wear out.
If the nuts are loose, tighten the upper ones. Since the engine rides on the lower ones this won’t affect the alignment. If you change the position of the lower nuts you’ll have to realign the engine.
Pulling an engine or jacking it up to replace the mounts waterborne shouldn’t be a problem. I’ve done it ok. In fact it’s preferable to align the engine to the shaft waterborne as the hull flex is different when the boat’s out of the water. If you’re disconnecting the shaft from its flange waterborne you need some hose clamps on the shaft so it doesn’t slide out the stern tube by mistake
Engine alignment takes preparation and a lot of patience. Read up on it beforehand. Too much to address here. You may want to talk to a marine mechanic about shimming and aligning the engine if its not running smoothly.

Walt Elliott
Kingston WA
Puget Sound
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post #5 of 7 Old 05-30-2011
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Sounds like those mounts need to be replaced. Don't know why the boat shouldn't remain in the water--and as someone else said, that's where you're going to need to do the realignment. We replaced the two forward mounts on our 2GM20 with the boat in the water--used a screw-type car jack to lift the engine just enough to slide new mounts under--engine detached from the shaft, of course.

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post #6 of 7 Old 06-01-2011
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I've pulled both my Yanmars and replaced the mounts while the boat was in the water.

I don't know the difficulties of doing this in your boat. In my case I used my boom to lift them out.

Tropic Cat

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post #7 of 7 Old 06-05-2011
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I'll just share that I replaced the mounts on my Universal M40 last year and it was one of the best things I've ever done. Pretty easy. I have a PSS seal and that was no problem either. In the water, used 4X4 over compainionway and a come-along. While up, I was finally able to really clean under the engine and tighten the bolt on my sump hose so it would stop leaking.

Hardest thing is getting the clearance to within specs on the flanges. Adjust, lower, check. Raise, adjust, lower, check. Repeat a few times. Really reduced vibration in my boat, and now a year later my cutlass bearing is still like new in terms of play. So the alignment held.

Good luck with yours. Nothing to be too alarmed about. Calder has good descriptions.

Gulf 32
Bainbridge Island, WA

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