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Engine vibrations

The engine in my narrowboat, a 3 cylinder Thornicroft 60 on oil filled mounts, is fine when on tickover, but as engine speed increases it starts to vibrate until between 800 and 1000 rpm the vibration of the engine is quite violent. Then at 1100 rpm the vibration stops and doesn't reoccur at higher revs. This has occurred over the last year, before which it ran smoothly at all engine speeds . Any suggestions as to a likely cause. The mounts are about 15 years old.

Asked by: Ian Burns  | 11.17pm, Tuesday 31 July

WW says:

Both the engine and the mounts have a natural frequency and these need to be compatible so that the mounts work properly at all engine speeds.

  • I am not familiar with oil filled mounts but, if your mounts are 15 years old and worked perfectly until a year ago, it seems that they have recently deteriorated.

  • The first thing to do is to check that none of the fixing down bolts are loose and tighten them if they are.

  • A more likely cause is that your mounts have recently started to leak or they have simply worn out which has altered their natural frequency and caused the engine to vibrate at certain speeds - unfortunately the speed you probably use the most.

  • One way to test this theory - and possibly cure the problem - would be to replace the mounts which, while not a five minute job, shouldn't be as difficult as it sounds.

  • Assuming that your engine is Mitsubishi based, you could consult Craftsman Marine or Vetus, both of whom sell Mitsubishi based engines. Contact details are -
    www.cheshiremarine.co.uk 01270 522000
    www.vetus.co.uk 023 8045 4507

    Graham Booth  | 11.37AM, Wednesday 1 August

    It sounds like you have Vetus Hydrodamper mounts, which are particularly useful for single, two and three cylinger engines, and have been standard Vetus supply on their mitsubishi engines for a long time. You may find that the mounts are time-expired- and also that it is worth checking the alignment as well. If the mounts have dropped, there may be direct metal-to-metal contact rather than through the rubber/fluid damper.

    Mark Langley  | 4.46PM, Thursday 2 August

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