Thanks & Advice on Engine Mounts

[ansusna]

This website and the Tech-Note are really great!  I would like to personally thank everyone that contributes.  The first three bullet are my success stories.  The fourth contains my questions.

1) Our heat exchanger was leaking at the couplig for the zinc, so based on Ron Hill’s advice, I had the heat exchanger repaired by a radiator shop for $65.  That was after the marine diesel mechanic told me that it could not be repaired.  Works like a charm, and the engine runs at a nice cool 160 F.  That saved us about $350 bucks!

2) I rebuilt the Oberdorfer raw-water pump according to the tech-notes article, and replaced the coolant pump along with all of the hoses.  Both pumps had been weeping, and were causing some corrosion of the oil pan.  I purchased the coolant/water pump from a Kubota dealer for about half the price of a Universal Dealer.  Thanks again, saved another $100.

3) I used the gore-tex stuffing material that Ron Hill recommends so strongly.  That also worked like a charm.  I just hand tightened the packing nut until the leaking stopped; the coupling was just a little warm at 2300 RPM with no noticeable leaking.

4) The engine mounts - here is where the questions start.  We decide to upgrade the engine mounts with K50’s on the front and K75’s on the rear.  I disconnected the coupling, and the exhaust riser.  We had some trouble with the method of only lifting half the engine described in the tech-notes, so we just lifted the whole thing.  

This weekend we started up the engine and she ran well at idle in neutral except that the engine is a either a little bit further forward or not at the same elevation as before, which caused the spline for the crankshaft pulley to rub against a screw that holds sound proofing to the inside of the lower step.  I loosened the mounts, but was not successful in pushing the engine back any further.  I figure that worst case, I can move the screw and the spline would only rub against the soundproofing.  

**  Any suggestion?  Moving the engine back probably means lifting her up, taking the mounts off and filing out the holes.  Also, we used the same lag bolts, I don’t understand the comments made on the message boards that we would need shorter bolts with the new mounts?

When I put the engine into forward at idle there is awful racket, less so in reverse but still vibrates a lot.  I was fairly sure that I had the engine aligned following several methods described in the tech-notes and on the message board, but I became nervous and convinced myself that the problem was from the shaft hitting the stern tube.  Obviously, I am not the first person to experience this problem.  I did not see a conclusive “solution” posted in all of the discussions other than raising the RPM’s.  I disconnected the shaft and lifted it up and down until it hit the tube, and tried to center the shaft.  I think that I got the shaft aligned again with the coupling, but this time I was less sure as the shaft seemed to move to the right very slightly when I push the shaft forward to mate with the engine.  In any case, we took the boat out.  If I rev up the engine, I can shift without too much vibration.  She is very quite in neutral.  There is a little more vibration than I expected at all RPM's (although not bad and less than before), so I am thinking that the shaft is not aligned properly.

We did not replace the shaft coupling because of funds and a desire to finish the project and go sailing.  I also spoke with a diesel mechanic who basically told me that they are a waste of money, and I should just align the engine properly.  I am beginning to loose faith in diesel mechanics!  I am now wishing I had replaced the coupling.

**  My plan at this point is to work on some/all of the items below.  I am looking for some outside opinions and/or which item below is the best place to start.   Or perhaps I am way off base and should try something else entirely.  

(a) spend more time trying to re-align the shaft and/or have a mechanic look at the alignment.  I am not convinced this is the cause of the low RPM nosie.

(b) replace the coupling with a flexible coupling.  My understanding it that this means lifting the engine again, and disconnecting the exhaust riser again.

(c) replace the front mount to K75’s for a stiffer mounting.  

(d) raise the engine idle to 1000 RPM (actual)

Andrew & Tami
“Cheers”
1987
Hull #471
Engine: M25XP

[Mike and Theresa Vaccaro]

Dear Andrew,

We've replaced our mounts with 4 K50's and added a bullflex coupling, and have almost no vibration at any power setting other than idle (all disels vibrate at low RPM to some extent).  Sounds like an alignment problem.

The flexible coupling dosen't alieviate you of the requirement to properly align the motor (as RPM increases a flexible coupling's "tollerance" for misalignment diminishes).  It's really designed to damp vibration that would normally be translated to the shaft.  So in that sense, your mechanic's right.  It's really a matter of spending quite a bit of money for a minor improvement.

The alignment problem could be the result of using the old holes in the limber mounts.  The Vetus mounts have holes vs. slots and it may be necessary to either file the hole larger, or fill your old holes with epoxy and re-drill.  The reason for shorter lag bolts is that the feet of the new mounts are about 1/2 inch thinner than the stock mounts (which also have slots allowing for lateral alignment).

You might take a look at the projects page for some photos/notes about the Vetus flexible coupling installation.  The coupling can be changed without un-bolting the engine, although you may have a difficult time removing the old coupling, forcing you to lift the engine out of the way.  If you use a Vetus Bullflex, you can actually cut the shaft, saving quite a bit of work.  BE SURE THAT YOU'VE GOT SUFFICIENT PROP CLEARANCE AT YOUR RUDDER ANY TIME YOU REPLACE A COUPLING!

If the engine is properly aligned (in the water with the boat at "operating weight"), then vibration could be the result of a worn cutlass bearing, worn shaft or an imbalanced/bent propeller.

Please drop an e-mail if you have any specific questions.

Best of luck!

Mike

[ansusna]

Thanks for the advice!

I installed the vetus bullflex flexible coupling this weekend.  That horrible low RPM noise is gone!  There is just a slight vibration at very low idle when in gear.  

I didn't make any major changes to the alignment, and I didn't increase the idle RPM.  Does anyone have the K50 mounts and a rigid shaft coupling?  I'm just curous at this point.

[Mike and Theresa Vaccaro]

Andrew,

Glad it worked out for you.  Think you've got a valid question.  We put the flexible coupling on at the same time as the new mounts based on a suggestion by the folks at Vetus.  Believe that the theory is that the flexible mounts isolate the engine from the limber mounts by allowing it to vibrate rather freely at low RPM.  Suspect that if the coupling is rigid, much of this vibration is still translated to the hull via the shaft, and shaft strut.

Cheers,

Mike

[skip]

Andrew-

Changed to K50 mounts and kept rigid coupling for last year.   Had symptoms similar to you with a definite roughness at low rpms in gear.  I aligned the engine very carefully with measurements first (I had pulled the whole engine to change the transmission) then repeatedly when the boat was in the water.  I also have had my cutless changed within the last two years and a new maxprop put on.  Put the bullflex on this spring and there is a significant difference.   While it isn't conclusive, sure is convincing.

Regards-
Skip

[Kelly Steck]

I had the same rattle and noise on my K50 conversion.  My solution was to put a cuttless bearing into the fiberglass tube right behind my Stuffing Box.  Works great and eliminates some of the alignment issues of the shaft as it is preset in the center.