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Old 11-07-2013, 08:47   #1
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Engine Mounts

Background:

Volvo MD 17D w/. power take off to a compressor which is mounted to the bulkhead uses 2 belts. Refer Compressor is hinged and a spring provides tension for the belts. The flywheel is perilously close to the compressor case... but if things remain as they are ... no problem.

Recently we were motor sailing and heeled over and heard occasional knocking which turns out to be the flywheel banging into the compressor when it was not operating. This led to the paint being stripped off the flywheel as it was being ground by a bolt mounting (not used) on the compressor.

I am trying to figure out what's up... My thoughts are as follows:

1. The engine mounts are soft (bolts are tight) and allow the engine to tip a bit toward the compressor when heeled.

2. the compressor belts (replaced last year) may be a tad too short pulling the engine closer to the compressor

3. the spring is too weak and doesn't hold the compressor away from the engine (enough)

When I step / push down on the compressor belts BOTH then engine and the compressor move toward each other. I can't remember if this is normal... But the engine mounts of course have some flex.

This system worked for 20 something years although over the last several I did notice some paint wear on the flywheel. it only seems rather exaggerated and the knocking noise is evident.

Is motor sailing heeled ill advised? How much heel would be acceptable if any when motoring? Of course without the compressor this condition does not exist... but then the refer is useless.

There's little to possibility to reposition the compressor. I wedged a block or wood between the engine and the engine room bulkhead which prevents the engine from moving in that direction. I am thinking of replacing the wood with a threaded metal pipe to resist the engine movement. Is this a crazy idea?

Thanks for your comments!

Jef
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Old 11-07-2013, 08:50   #2
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If your mounts are 20yrs old, then it's time to replace them. The rubber does wear out over time.
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Old 11-07-2013, 08:56   #3
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Re: Engine Mounts

Thanks... I was thinking the same. Is that a DIY job or does the engine have to be moved by pros?
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Old 11-07-2013, 09:24   #4
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Depends on your skill level. Do you know how to align the engine? Are you handy using levers and wedges in a confined environment to remove and replace the mounts? Do you have the time to do this?

I've done mine (but I've also pulled the engine into the salon just to clean and paint it and the engine compartment).
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Old 11-07-2013, 09:53   #5
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Re: Engine Mounts

You CAN remove the engine completely, using the main halyard, through the companionway. That will give you much more room to overhaul the engine room make repairs and touch up the engine, easily replace the mounts, etc. Then, when the engine goes back in you will have really received a major bang for your buck and hours spent. Alignment is mostly lifting, wedging, twisting until the coupling on the shaft sits closely on the engine coupling. My alignment is within .004", about as close as I can get. I have a 17 foot by 1 inch prop shaft, with pillar block bearings, shaft log and cutlass bearings within 40 inches of each other. Engine runs smooth with virtually no vibration to speak of. The actual alignment can take as little as a couple hours, doing it yourself. It's always easier to have someone at the other side of the engine, or to hand you tools. You'll really appreciate good lighting, too.
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Old 11-07-2013, 15:41   #6
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Re: Engine Mounts

Thanks guys. I may attempt this in the slip during winter storage. I can always bail and have the yard mechanic finish. I'll order the mounts and get things prepped. I'd like to leave the compressor in place and not have to re charge it. And that will make removal a bitch. One Volvo mech who knows my boat said I need to only raise the motor an inch or so and to replace one at a time. We'll see... I have to plan this.
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Old 17-07-2013, 12:39   #7
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Re: Engine Mounts

More...

I am trying to determine how flexible an engine is expected to be with typical engine mounts... new ones and old ones.

The elements ARE elastic and expected to dampen vibration and so they MUST allow for some sort of lateral movement. But how much?

I've determined that when the boat is heeled to 15 or 20 the engine tilts about 1/4" maybe a bit less. I suppose I could get accurate measurements next time I am heeled over. There is no unusual vibration in the motor... nothing new. aside from the usually annoying one at some low rev... but that's not too bad and I just avoid that RPM setting.

Before I go to the expense and trouble in replacing the mounts I'd like to know what to expect from them and what are the signs that they are no longer doing what they are supposed to be doing.

any comments?
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Old 17-07-2013, 12:59   #8
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Depends a lot on the mounts. Yammer mounts are extremely soft and allow a lot of movement but may not be suitable for your application. I've got rather firm PYI mounts, I chose these over softer mounts to keep the engine still. They do transmit more sound to the hull at lower speeds but are quieter at higher speeds
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Old 17-07-2013, 16:49   #9
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Re: Engine Mounts

The tipping problem only manifests as the running engine flywheel hitting the compressor and so maybe the mounts are OK as I rarely every motor heeled over more than a few degrees for motor sailing. I suppose they COULD be stiffer and I might find a way... complex... to move the compressor a bit...and that will be less costly that new mounts and so forth. Obviously this problem exists only when heeled to stbd. The lack of space limits the solution options.
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Old 17-07-2013, 17:27   #10
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Re: Engine Mounts

Look at the mounting brackets on the motor, you maybe able to change one at a time by removing bracket & mount readjusting the bottom nut each time to keep the alighment. It may save lifting the motor. (just done it) Had to stand on the spanner to undo the bolts!!

Regards Bill
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Old 17-07-2013, 18:44   #11
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Re: Engine Mounts

Bill,
This is exactly what I would do... and yes I have to remove the alternator and the compressor to get at the front mounts. This way you can maintain the shaft alignment and the motor position. I am going to tackle this in winter storage.

Thanks!
Jef
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Old 17-07-2013, 18:58   #12
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Re: Engine Mounts

sounds like your engine mounts are very soft if the engine moves when you tension the belt! Otherwise I'd say get a stronger spring for the compressor.....
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Old 18-07-2013, 06:24   #13
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Re: Engine Mounts

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Originally Posted by Cheechako View Post
sounds like your engine mounts are very soft if the engine moves when you tension the belt! Otherwise I'd say get a stronger spring for the compressor.....

No the engine does not move when I tension the belts... but there is a caveat to that. The spring tension has not effect... I moved the attachment point further to add some tension.. and it was a bitch to do that.

If I step down on the two compressor belts... since the compressor is hinged... it will cause BOTH to move a bit... not JUST the compressor and not JUST the engine.

Yes... the mounts may be a bit soft. And that is what I am trying to determine. Mounts ARE meant to be flexible and soft... but the question is how soft and how flexible.

My compressor location is very close... tolerance separation is very small. As I don't run the motor when heeled a lot this condition or hitting the flywheel does not manifest. When I do motor sail.. this does not happen.

Further.... I was getting some "banging" when the compressor clutch was engaged for a few secs... apparently until it got up to speed and settled in. This was something new... the sound... and I thought it was a bum compressor. However... I tightened the spring and the sound has stopped on start up.. so the spring may have lost a bit of its spring tension!

Obviously mechanical system do degrade over time... belts, springs and elastic mounts. I got that. I am just trying to sort out what needs to be replaced etc.

Thanks for your comment!
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