Excessive Vibration/Noise

[Julian Elliott]

Yesterday, when cranking the engine on Tenaya, I experienced a quite noisy shaking when the engine is in Neutral below approx. 1500 RPM.  (Same in gear, obviously).   3 weeks since last startup, which was fine.  No exhaust smoke, proper cooling water circulation, etc.  Can't honestly say the engine was vibrating excessively, but the noise scared the hell out of my wife.

From prior posts, I suspect the motor mounts, which I'll check more closely this weekend.  A couple of questions before I poke around:

Is motor mount failure rare on an 8 year engine?  Any other likely culprit?  FYI, it's a 2005 Mk II with M-35B engine.  Since it occurs in neutral, I'm assuming the shaft linkage, etc. is not the cause.  Would injectors or water in the fuel cause this?  Engine revs fine at higher RPM. 

Will a worn mount be readily apparent?  What should I look for?

Thanks.

Julian

[sail4dale]

It sounds like misfiring.  I would suspect the fuel system .... injectors not performing ...or  bad fuel with maybe water in it.  at higher speed it would seem to diminish but possibly still missing.   if it was a gasoline engine the first thing would be spark plugs going bad and causing the engine to miss.  Since a diesel has no spark plugs
to cause the problem the only other thing is the fuel system causing the misfiring.  IF that is not the cause ....  would get the compression on each cylinder checked.

Just some thoughts from and old time engineer,

[Jim Hardesty]

Julian,

Do I have this right.  Engine was running OK.  After sitting for 3 weeks, the engine started.  Had more than normal noise and vibration.  Was not run for very long and was shut down to be looked at later.  I assumed the last because you said "scared th hell out of my wife" never a good thing to do. 

If I have that right, I would think first of a small fuel leak at the injectors or the high pressure pump.  ie The small metal tubes not the hose like lines.  Theory, fuel leaked out and air leaked in.  If I guessed right running the engine longer, several minutes, would have stopped the problem when the engine self bleeded.  I would not have done that except in an emergency.

Next trip to Tenaya, do a good engine check.  Check for loose anything, alternator, exhust, air cleaner.  Look at the water seperator fuel filter for any water in the bowl.  You could look at the engine mounts for anything wrong, I don't think they are your problem.  Look for any trace of a leak at the injectors.
 
Then start the engine.  If it still vibrates, shut it down and bleed the fuel system.  Do a search here.  Lots of how to bleed the system.  Restart, it may take a few minutes to get the air out.  If that fixed it I would tighten the fuel lines at the injectors.  Be careful, only tighten the tubeing nuts don't damage the tubeing, use good wrenchs.  If it doesn't run normal after a few minutes, it may be bad injectors as posted by sail4dale.

Back to your original question about engine mounts.  Two seperate types of engine mount failures.  One is broken or damaged from the rubber seperation ,the hardware loose or broken or chemical damage (oil from messy oil changes getting on the engine mount).   You can visualy see that or use a pry bar if in doubt.  The other failure is wear/age to the rubber.  I don't think that your boat is old enough to have that problem.

Hope this suggestion helps. And a Happy New Year to all.
Jim

[Julian Elliott]

This is very helpful, and reinforces my suspicion that a possible cause may be  water in the fuel or an air leak.  Condensation is a problem here in the NW, and I'll check.  I have also had seepage of diesel as well, and going a long period without running may have introduced air in the line.  Good ideas. I'll add to my list. Thanks.

Julian

[Ron Hill]

Julian : You can do as Jim suggested, but I think you have an injector problem.

One or two of your injectors are not "popping" correctly or the spray pattern is insufficient for the engine to run smoothly at the lower RPMs.  Here's what I'd try:
1. Fill a new engine mounted filter with PS brand diesel injector cleaner and bleed that filter with the bleed bolt on the top of the mount (don't overbleed - just enough to get any remaining air out of that filter!).  Then start the engine and see if it smooths out as the injector cleaner does its job.
2. If that doesn't work, remove the injectors and take them to a injector shop where they can check the pop pressure and spray pattern and general overall operation/condition.

I've written a number of "How To remove the injectors' articles in the Mainsheet tech notes.  Also look in WiKi and Projects.

Hope this helps

[Julian Elliott]

A quick followup:

Turns out my two forward motor mounts were loose.  There are two 24 MM nuts above and below the engine bracket on each mount;I assume the lower nut backed off a half turn or so.  I tightened the lower nuts (upwards) which completely solved the vibration.  In gear, the alignment seems ok, but I may have it aligned  eventually to be sure.  But I'm happy now.

Comments here motivated me to also change, for the first time, both fuel filters and bleed the system.  Was surprisingly easy, especially compared to my prior 320, which was always a nightmare.  The self bleeding system makes this very straightforward.

Thanks for the advice.

[lazybone]

A quick followup:

Turns out my two forward motor mounts were loose.  There are two 24 MM nuts above and below the engine bracket on each mount;I assume the lower nut backed off a half turn or so.  I tightened the lower nuts (upwards) which completely solved the vibration.  In gear, the alignment seems ok, but I may have it aligned  eventually to be sure.  But I'm happy now.

Comments here motivated me to also change, for the first time, both fuel filters and bleed the system.  Was surprisingly easy, especially compared to my prior 320, which was always a nightmare.  The self bleeding system makes this very straightforward.

Thanks for the advice.

I love it when we get a follow-up.

Thanks Julian

[Ron Hill]

Julian : Loose engine mounts will do it every time!!

To preclude the engine mount nuts from backing off, you can take another nut and put on top of the top nut so it acts as a jam nut.  Then crank the top and bottom nuts tight - so nothing can move.

Another item I wrote about beside jam nuts are slippage marks.  Make a mark (thin line Sharpie or paint) on the nut that extends on to the engine mount bracket.  If you notice that the mark doesn't line up anymore, it tells you the nut is backing off.

A few thoughts

[Ron Hill]

Julian : While we're talking about the engine mount adjusting nuts; don't forget to insure the tightness of the lag bolts that hold the engine mounts to the engine bed!!

I'm sure that you are going to check your engine alignment, before you use the boat again. 

A thought

[Julian Elliott]

Good ideas, Ron.  There's surprisingly no lock washer on the mounts, so a second lock nut would prevent a re-occurrence.  FYI, one lag bolt was in fact  loose; everything snug now.

[Stu Jackson]

Julian,

Thanks for the feedback.  G;ad you found your issue.

If yo simply tighten the lag bolts, you are NOT necessarily out of the woods.  You NEED to find out if they bed when tightened.

If you do a search on this board on "toothpicks" you'll see what I mean. 

[Jim Hardesty]

Julian,

I'll repeat, thanks for the feedback.  Glad you found your problem, and that it was a simple fix.

You should consider checking the engine alignment.  Checking is not difficult at all, should not take much time.  The alignment will take a while, can be tedious and the aft starboard mount is not easy to get at.  Don't know if a how to has been posted here, but Don Casey's book "This Old Boat" was my guide for that and many other projects.

A misaligned engine may cause cutless bearing, shaft and shaft seal wear and vibration.

Just a suggestion,
Jim