Engine Movement

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This topic contains 9 replies, has 6 voices, and was last updated by  Mark Schwall 4 months ago.

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  • #8902

    Mark Schwall

    Hello everyone…new members here. Cathy and I recently purchased Lone Wolf from the McQuades and have renamed her Midnight Blue. Our starboard engine has movement compared to the smooth-as-silk port engine. The owner’s handbook says that is normal for one engine to vibrate slightly more. The prop and the shaft checked satisfactorily with a micrometer, the cutlass bearing has zero movement, and the engine mounts are solid. Is this movement something that other GH owners experience? We don’t want to create further problems unnecessarily. Thanks for your guidance.

  • #8904

    Norm Miller

    I too have one engine that seems to vibrate more than the other ( not excessive but not as smooth as the port engine). On mine I have checked the alignment of the coupler with it unbolted and it is within 5-1000s so so far I have ignored it, but will check coupler alignment again this winter during layup (Dec to March..we winterized in Indiana this time of year).

    Curious to see what others say!


  • #8907

    Henry Dennig

    I believe Dick Hermann on Avocet chased that very issue last year. What he found was the shaking was attributed to his transmissions.

  • #8908

    Hi Mark,

    Welcome to the GH family!

    Henry is right, and the road that led us to rebuild our transmissions was long. We checked propellers, shafts, cutlass bearings, and replaced the engine vibration dampers. We serviced the fuel injector nozzles on the main propulsion engines. We also replaced the engine mounts and fabricated more robust engine support brackets on which the engine mounts rest.

    At long last, we compared the difference between minimum and maximum rpm’s as a percentage of averages rpm’s of the prop shaft to the difference between minimum and maximum rpm’s as a percentage of averages rpm’s of the engine main pulley. (A photo tachometer that captures min, max, and average rpm’s is needed for this diagnostic.)

    We found that the prop shaft had greater variation than the main engine. This indicated that the transmissions were slipping momentarily, thus causing the vibration.

    Mastry Engine Center, master distributors for Yanmar engines and Kanzaki transmissions located in St Petersburg, FL rebuilt both transmissions. They were astounded to find that the adjusting nut – which is torqued and then peened into a groove at the factory so that it will never come loose – had loosened on both transmissions. Mastry had never seen this in more than 30 years of rebuilding Kanzaki transmissions.

    The odds of having this happen to both transmissions at the same time must have been, literally, one in a million.

    It cost about USD 1850 to rebuild each transmission. We spent considerably more than that on the other work.

    I hope this helps. Feel free to call me if you want to talk about our experience in more detail.

    Dick Hermann
    Great Harbour N37 Avocet

  • #8911

    John Reynolds

    Absent a mechanical problem such as with Avocet, the different vibration characteristics between the engines could be due to the transmissions, one being operated in “forward” and the other being operated in “reverse”. There are more gears involved when the transmission is in reverse. See the attached file.

    As such it could be considered normal.

    You must be logged in to view attached files.
  • #8919

    Mark Schwall

    Thanks everyone! I forgot to mention that the movement was identified during the per-purchase survey so the first thing we did was perform a prop shaft alignment which fell in at 4-1000ths. The engine vibrations are comparable. The movement is evident in the prop shaft. Based on everything I have checked to this point and Avocet’s experience, I think I may have the same issue in that starboard transmission. Thank you for sharing Dick! My next move was to pull the prop shaft and send it to a machine shop in Brunswick. Instead we will bring Midnight Blue to the St Pete Municipal Marina sometime in 2018 and have Mastery Engine Center diagnose/repair the prop shaft movement. I appreciate all the help!


  • #8926

    Chuck Truthan

    Number one, check the age of your engine mounts. They are a service life limited item and should be replaced every 10 years (or is it 5 years?).
    Number two, check the stringer mounts – if they are the straight 90 degree aluminum angles without gussets, then change them to ones with gussets.
    Number three, if it is the starboard engine that vibrates more, and by this I mean is smooth but just vibrates, not JUMPS around like when the transmission is going bad, then you want to also add backing plates to the stringers.
    When we bought Insandity (neigh Pelican) it had a history of fracturing both forward engine mounts on the starboard engine around 400 hrs. When we did a PM replacement of the engine mounts around 3,000 hrs. last year, we found the inboard, forward mount was fractured. The shop then could not get the alignment with the prop shaft and the mechanic noticed that with the engine running, the stringers were bending inward. This is the exact motion needed to provide the sheer stress to fracture the engine mount bolts. Once we added the stringer backing plates (both sides of the stringers, both inboard and outboard on the starboard engine and inboard on the port engine – as there already is a backing plate on the port outboard stringer for the generator floor) the engine aligned perfectly and BOTH engines purr with the same vibration. We also changed the stringer to engine mount brackets to a single 90 degree aluminum angle with three gusset plates per bracket.
    Unfortunately, this fall, the port engine is BUCKING for the first 10 to 15 minutes in the morning, but after letting it “drag” in neutral, it then runs smoothly the rest of the day. This is what Dick Herman’s engines were doing as well. He got suckered into “prop whip” before discovering the transmissions were bad on both engines.

  • #8936

    Mark Schwall

    Thanks Chuck. I’ve spoken with Joe Pica regarding the similar issues he had with Carol Anne. It seems to be a common problem with these boats. I’ll certainly look closely at the engine mounts.

  • #8940

    John Reynolds

    Attached are two pages from the Yanmar Marine Engine Installation Manual. The first page states that it is not advisable to bolt an L shaped angle to the engine bed (as was done by the builder). It shows a picture of the engine stringer mounts with gussets as discussed above. The second page states that the engine mounts should be replaced every two years., which I never did. I would suggest contacting several diesel experts, e.g. First Mate Yacht Service in St Augustine, Mack Boring, Mastry, to get their input on replacement interval.

    The Yanmar Marine Engine Installation Manual contains a lot of good information. I would be happy to upload it to the library if someone could tell me how to do it.

    You must be logged in to view attached files.
  • #8955

    Mark Schwall

    Awesome! Thanks John! I’ve recently discovered that the prop shaft was replaced 2 years ago so it must be either the transmission or the engine mounts.

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