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Excessively noisy gear box


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Hello fellow boaters,

  it has been some time since my last confession!  
 

My boat is fitted with a Barrus Shire 45 (series 4) driving a PRM gearbox.  Over the years I have gone to great length to reduce the noise level of the engine but still, when cruising, the sound from the engine bay makes it all but impossible to here people on the bank side.  Today, when coming down the locks on the Erewash Canal shared with another boat, the helmsman said ‘you’ve got a noisy gearbox’!  Wow, with those few words I realised the source of the ‘din’.  Now, I have to identify what I need to do to resolve the problem.  
I will try and help, firstly with the obvious:

Oil and oil levels OK

Hours run ‘difficult’ ‘cos the hours counter on my Shire delux panel gave up a few years ago, but not more than 7000.

 

any other questions that might help identify why the noise exists- please ask.  I will provide what answers I can and photos can be supplied.

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Strange. Gearboxes are not usually noisy until they are about to fall apart. There are some gears, they either mesh or ultimately don't, clutch assemblies, they either work or don't and some bearings that rumble. Not sure what the base engine is but I think as its been going on for a long time and it still  runs I would really suspect the exhaust. If someone has fitted a silencer from a car breakers it might be hopeless for a diesel. A friend fitted a lovely chrome motorbike silencer to a Lister, If anything it made the damned thing even louder.

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If the engine is flexibly mounted, I would want to ensure it's not the engine bouncing about banging the shaft about in the shaft bearings. Most "flexible" couplings will not take up radial displacement caused by the engine jumping about. Have you done a search for the noise using a listening stick between your ear and various parts of the boat.

 

Hardening gone/worn off the gears is likely to whine and as Bees says bearings tend to rumble. Any chance of a recording, although they tend to be hard to diagnose from.

 

Just seen Brian's post - photos?

Edited by Tony Brooks
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OK, 

 I do not have a silencer from a car breakers yard, I have a correctly specified and fitted ‘hospital silencer’!  Having had it fitted the vibration from the power unit reduced very dramatically - but this is not our problem.  The noise is generated when selected into gear - out of gear the noise from the engine is minimal.

The ‘base engine’ is a Yanmar TNE.  It noise has been like this from new.  

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I will see if I can record and post the sound from the drive train.  I will also photograph the set up to see if there is anything identifiable.  It has been like this for 17 years and todays was the first time someone said ‘it is the gear box’.  Makes sense tbh!

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Unusual problem. If it makes a racket when in gear I think I would still not suspect the gearbox as I think it would have turned into a pile of broken things on the floor by now. If the drive train includes an Aquadrive or Python drive I might wonder about the thrust bearing that these things have , its a hefty bearing but as its bolted (via rubber pads) to the hull that would amplify the noise. Same goes for a plummer block as that is bolted through metal to the hull. It is an odd problem though as if it was badly aligned or bent shafting you would expect a leaky stern gland or  some obvious failure by now 

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Ok everyone, thanks for the suggestions - all food for thought.  I think I should have titled this thread ‘Excessively noisy drive train?’.  It has been like it since new so I am of a mind to consider Bee’s more recent post.  I guess it is ‘just how it is’!  It has taken me across the Wash, down the Severn Estuary and round the Ribble link without any problem - other than the noise.  
I will use a listening stick to try and identify what particular component is the culprit.

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