Twin Disc gearbox

[Sinbad2905]

Afternoon all

My motor boat is fitted with a Twin Disc gearbox (model MG5061SC) which has developed a slight oil leak from the output shaft.

I have been advised that the gearbox has to be removed to replace the seal, and have been quoted an eyewatering £1800 for the strip down and seal replacement (the seal itself is probably only about £20.00). This does not include the actual removal and refitting of the gearbox. The quote is from a reputable company and have no doubt about their credentials, they categorically say the replacement of the seal cannot be done in situ.

The leak is probably only about a tablespoon full after every 3/4 hour trip. Would it be possible to add an additive to the oil to try and stop the leak, the oil within the gearbox is straight SAE40, or should I just put up with this leak and monitor it over the year or so. I do use the boat for about 250 hours per annum.

Thanks

 

[superheat6k]

It might be possible if you can pull off the output coupling. Once this is off then the seal is fairly accessible - exploded view page 86, diagram showing a puller P96. You will need enough space to mount the puller, but this could be a simple plate with bolts to pull up against a suitable socket.

https://www.dropbox.com/s/4efm2qh6u4lws3r/Twin Disc MG5114SC Service Manual.pdf?dl=0

 

[steved]

Thanks for the reply and dropbox link Superheat.

The manual in in the dropbox is for the MG5114SC and mine is MG5061SC so I'm not sure what differences there are.

The gearbox company that I approached (Marine & Industrial Transmissions Ltd) quoted the following:
'' Unfortunately the output shaft seal is not replaceable in the vessel, due to the makeup of this unit the output shaft and flange are all one part.
The output seal is the last thing you can get at when dismantling the unit and it is the first thing fitted to the unit on reassembly.
The unit will have to come out of the vessel and to our works to resolve this issue.''

So I'm just wondering whether an oil leak additive would be any good to try, or is this not advisable in a gearbox application.

Thanks all

 

[steved]

just noticed that I'm now logged back in on my original user name 'steved' which I couldn't do yesterday on a different computer as I'd forgotten my password... doh..

So 'steved' and 'sinbad2905' is the same person...

Thanks

 

[bristoljim]

Not familiar with that box but it seems it is like very early PRM boxes which had the main output shaft & output coupling made in one piece so total dismantling to change the seal. Sorry I cant offer any solution.
Jim

 

[bristoljim]

MIT should know what they are doing - looking at photograph of the MG506 there appears to be a disc in the centre of the output coupling with three set bolts,if the shaft & coupling are made in one piece anyone any idea what they are for ??
Jim

 

[anoccasionalyachtsman]

A faint hope for you - have you checked that the gearbox breather is clear? New engine oil doesn't leak as badly as thin old stuff, so a change will help.

Everybody's heard of the motor trade sawdust trick, but I did once try it in a Land Rover transfer box which I knew I'd be rebuilding anyway, and it did seem to reduce the leakage. Unfortunately for you the car was written off after an accident and I never did find out whether I'd done any harm.