Motor mounts & Shaft alighnment

Don12364 · Mar 30, 2011

A well covered topic. Try searching for 'knock' in title. Very many posts and answers.
e.g.
http://forums.hunter.sailboatowners.com/showthread.php?p=579207&highlight=knock

Maine Sail · Mar 30, 2011

rfrye1 said:
We are getting that "knocking" at +2400rpm. We had a new cutlass and new shaft when we had our PSS Dripless installed 18 months ago. Have about 60 hrs on the new shaft/cutlass. Knocking has been getting worst.

Had someone out and he says motor mounts are shot. The mounts were re-done 5-6 yrs ago. At $2200 to replace motor mounts I am wondering how long should they last? Does Yanmar have problems with mounts?
Thanks. Bob

Your aligner probably did not properly center the shaft in the cutlass or the shaft log before doing the "fine tune". Quite common. The other possibility is that it is aligned to the cutlass and the strut is crooked and not in-line with the shaft log, also happens.

RichH · Mar 30, 2011

In addition to the above, the shaft could have lost its 'true' ... it may have 'stress relieved and is no longer 'straight'. Happens with long thin shafts.

From you description it may be that a 'whole' job of alignment, including checking the shaft for 'trueness'' and 'run out'. Suggest that you disassemble 'the whole shebang': coupler, shaft, shlft log, strut, etc. and then start over from the beginning, but checking for the integrity of the motor mounts first.
Any misalignment that causes 'side loading' on the shaft should be remedied, side loading will cause the shaft to 'whip' or 'precess' especially as a harmonic vibration that is noticed at certain shaft rpms.

Bill Roosa · Mar 30, 2011

OR
I suspect that you had all the alignment work done while out of the water. A boat on the hard is being supported by the keel. A boat in the water supports the keel. the different kinds of stress result in flexing of the hull which can take a few days after launching to set in. It may just need the requisit tweeking after launch.

higgs · Mar 30, 2011

I have never had motor mount problems and have never owned a boat newer than 20 years old.

Snotter · Mar 31, 2011

It is possible. Many have motor mount issues and don't know it. You could be one of the lucky ones. A boat whose engine is bolted right to the engine bed may never need additional mounts. They vibrate I hear (I never owned one), but I bet they are easier to align and keep aligned.

Deadline · Mar 31, 2011

Given the work you just put into the engine and shaft, this is relatively easy.
Order the rubber mounts and put them in one at a time.
Then use a laser light with reflector to get the engine realigned.
Or use the thin alignment shims in back at the transmission.
Either way, the hard work and expense is behind you.

NYSail · Apr 1, 2011

wow... $2,200 to replace mounts. Buy and install them yourself and you will save over $1,600. I have done them on both boats I have owned. Take one out at a time, adjusting the new ones to the same height as the old ones. Then if you need a hand fine tuning the alighnment give someone a call....

Stu Jackson · Apr 1, 2011

Snotter said:
A boat whose engine is bolted right to the engine bed may never need additional mounts. They vibrate I hear (I never owned one), but I bet they are easier to align and keep aligned.

Aha! Just another reason to keep those old engine mounts!

Richard Bryer · Apr 1, 2011

Laser light with a reflector to get the engine aligned- anyone ever done this and how exactly did you go about it? I am just getting ready to install a new prop and shaft. Maybe thee is a better way to do the alignment?