How important is cooling...

[PuffTheMagicDragon]

...of the output bearing on a Volvo Penta MS reduction gearing? The reduction gear housing, in cast iron, incorporates a channel that goes all round the part where there is a large ball-bearing that carries the output shaft. The sea-water passes through this passage and then goes on to cool the engine (an old MD2 that is otherwise in very good shape and runs very smoothly). The reason that I ask is that I have found slight traces of water in the gearbox oil which, to me, would indicate that there is a leak from the water passage, probably through some corrosion in the casting. One solution would be to by-pass the passage of the reduction gear and take the water straight to the pump. Would this cause the bearing to overheat and lead to catastrophic failure? The cost of just the housing is around €1200 (plus VAT) to which one would need to add the cost of new bearings (at Volvo prices).

The other alternative would be to replace the motor with a new one c/w marine gearbox because I am not aware of any other gearbox that would fit instead of the MS.

A less expensive - if somewhat unorthodox - solution that I am toying with is to by-pass the sea-water as above and to circulate oil through the 'water' passage, incorporating a circulating pump and a header tank and copper pipe coil for cooling purposes; thus, any migration between the passage and the gearbox proper would consist of just the oil that would be of similar specs.

Any ideas/opinions anyone?

TIA.

 

[Bilgediver]

...of the output bearing on a Volvo Penta MS reduction gearing? The reduction gear housing, in cast iron, incorporates a channel that goes all round the part where there is a large ball-bearing that carries the output shaft. The sea-water passes through this passage and then goes on to cool the engine (an old MD2 that is otherwise in very good shape and runs very smoothly). The reason that I ask is that I have found slight traces of water in the gearbox oil which, to me, would indicate that there is a leak from the water passage, probably through some corrosion in the casting. One solution would be to by-pass the passage of the reduction gear and take the water straight to the pump. Would this cause the bearing to overheat and lead to catastrophic failure? The cost of just the housing is around €1200 (plus VAT) to which one would need to add the cost of new bearings (at Volvo prices).

The other alternative would be to replace the motor with a new one c/w marine gearbox because I am not aware of any other gearbox that would fit instead of the MS.

A less expensive - if somewhat unorthodox - solution that I am toying with is to by-pass the sea-water as above and to circulate oil through the 'water' passage, incorporating a circulating pump and a header tank and copper pipe coil for cooling purposes; thus, any migration between the passage and the gearbox proper would consist of just the oil that would be of similar specs.

Any ideas/opinions anyone?

TIA.

It is not unusual for this passage to suffer frost damage. It is always a good idea to flush the sea water system with antifreeze or drain this chamber in the winter if the boat is ashore.

Usually in the UK this passage is not really required and can be by passed. The best thing to do is by pass it and then check that the bearing housing is always just warmish and not hot. It would be a different matter in the tropics. A few folk have reported that by passing did not give a problem.

If By passing then seal the end connections so flooded bilges will not put water in the gearbox.

 

[Gordonmc]

I suspect you will need some external cooling with your option 2. It's not uncommon to route engine cooling waater through a gearbox oil heat exchanger for this reason. That should not be too difficult to achieve if you put a cooler in-line with the bearing oil feed.

 

[david_bagshaw]

do your by pass , bung one end on the gear box, pipe on the other fill with oil, rununder load, see if it leaks into gear box. if so, in time the gear box might overfill using your method.

if it does, fit oil cooler, pump and flow and return from gear box, .

if not, the water is getting in by some other route