Balancing Engine Weight While Aligning - SailNet Community

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Old 04-15-2009
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Balancing Engine Weight While Aligning

I just installed four new motor mounts on my Yanmar 3HM35F. After several attempts I can now get the engine and shaft aligned in a reasonable amount of time. But, I discovered that the engine and shaft will align properly but the engine weight on the mounts may not be evenly distributed.

How can I make sure the weight is properly distributed on the mounts while aligning the engine and shaft.

John L.
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Old 04-15-2009
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Don't know for sure but I'd make sure the engine mounts bolts were all adjusted with the same amount of threads showing thru each of the adjusting nuts.
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If only it were that simple.

Adjusting so the bolts showed the same amount of threads may help distribute the weight, but it doesn't align the engine!
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In theory you should be able to have both exact alignment and fairly even weight distribution. The weight distribution wont be exactly even since different corners of the engine weigh different amounts. I think you need to keep working on the adjustment. First get the coupler in the correct location with the mounts closest to the coupling, then align it with the mounts farthest away from the coupling.
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PYI sells engine mounts to stand for different weight, based on engine type/model. In my case, the front mounts were suposed to withstand higher weight than the rear ones. I just focus on alignment, and leave to the mounts to carry the load. Your Yanmar dealer should be able to recommend specific mounts for each corner/side ....
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Old 04-16-2009
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SteveInMD, that sounds reasonable. We are taking a couple of days off this project and we'll try again this weekend. Thanks.

negrini, yes, several of the smaller Yanmar use different mounts on different corners. My 3HMF5F however uses four of the same mounts. This is confirmed in my Yanmar manual and three different Yanmar distributors.

Thanks.

John L.
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Old 04-16-2009
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The minor difference in the height of the motor mount locking nuts to properly align your shaft will have virtually no measurable effect on the weight distribution. A 2" difference in the height of the supports from side to side only moves the CG about 4/100's of an inch toward the low side. A 3" difference for forward to aft only moves the CG about 6/100's of an inch to the low side. You body weight on the cockpit seats has far more effect.

FWIW...
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Redfish... It's really tricky to get it right. Good luck - I know what you are going through.
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Redfish, the balance of engine weight isn't something you can control so don't worry about it. Instead make sure you support the drive shaft so that it's not sagging and giving you a false reading. If it's a relatively short drive shaft then it may not be an issue, but I'd check to see how much vertical play there is in the shaft prior to performing the alignment and support it accordingly. The tolerances betwen the two plates are usually in the .004" range with a +/- of .001". (check your manual for the exact specs for your engine/boat) If the drive shaft is sagging it won't have to be so by much to throw your adjustment off. Also make sure the edges of two plates are aligned all the way around. You don't want any side to side offset between them. Good luck.
Mike
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