Strange vibrations

Small engines, big engines, they all have them and they can affect the performance, comfort and even integrity of your boat.  


We are talking engine mounts, sealing blocks, feet – basically the rubber support that takes out most of the vibration from your engine and drive train. When your installation is new, everything (hopefully) is aligned correctly and so the vibration that causes discomfort and wear should be minimized. A few years down the the line, things can drastically change.  A few hundred to thousands of kilos are rattling around at thousands of revs per minute, turning propellers that move tons of water. 

The force is transferred through the gearbox, one or more couplings, the sterntube and the bearings that support the propshaft. Wear in any of those can have a knock-on effect to the others.  Once a problem exists, the numerous components – often from different manufacturers – make it notoriously difficult (and expensive) to diagnose.

As with all things, prevention is the best policy.   Start with preventing oil contamination, which is a fast but preventable way to affect your engine mounting performance.  Oil degenerates the volcanisation holding the components of the mount together. In a short period of time the rubber material will decompose and part company.   After this parting, component wear rapidly increases in couplings and bearings and at worst the engine can part company from the bed altogether, causing a dangerous and catastrophic failure of one or more components between engine and propeller. 

Annual maintenance should check the integrity of your mountings, ensuring they are clean, secure and correctly positioned.  Manufacturer’s guidelines will normally advise how often you should check alignment of shaft to gearbox; some couplings will affect this and require more regular checks.  A good idea is to put a blob of paint on the top nut and spindle to easily check if these nuts are still tight and in the position you originally put them in. 

Most of the engine mounts you will come across are the traditional 4 mount system, two for the front and two for the rear to include the gearbox.  Gearboxes will have their own mounts with larger engines.  Outdrives and saildrives have different arrangements that rely on a surface of the hull or transom.  Needless to say a failure there could become a big problem and all require regular maintenance and occasional adjusting.   Insurance companies will normally require proof of compliance with maintenance schedules in the event of a claim.

Don’t let these important out-of-sight items slip out of your mind when you organise your maintenance. 


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