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Bravo 3 leg Overheating gear failure

RJH

New member
In 2016 I purchased a brand new 4.2L 320 HP Diesel Mercruiser with a new Bravo 3X leg. The motor and leg was serviced when due, 100 hr intervals.
At around 50 to 60 hours the forward gear would not engage immediately and as the hours got closer to the 100 hrs the lag going into gear became greater. The service mechanics {mercury dealer} looked at the cone clutch as the oil was badly burnt with very little viscosity, so the cause was placed on the clutch.

The vessel was serviced another 2 times and each time prior the forward gear would lag before engaging, the oil was again badly burnt, so mercury suggested to the mechanics to fit their spray unit to cool the leg down {I actually thought this is a band aid fix as the problem had not been found} the spray unit caused massive cavitation and I could not drive it, so it was removed, and told mercury are redesigning the spray unit.

The next service they reversed the cone clutch and told me all will be good, the oil was again badly burnt. I was present at that service and the oil was so burnt you could smell it from 10 yards away and it had no lubrication properties.

At 450 hours I was travelling at 18 knots for 90 minutes in calm conditions when there was a load bang at the stern, I stopped and we had a clunking sound, so I called the mechanics and I asked them if I could slowly drive it back to the Marina, and was told yes but at no more than 5 knots.
As there was no rescue boat available I called a friend and he met us half way and towed me in.

The leg was removed, stripped down and found the main drive gear had broken in half. The oil was black and burnt and smelt bad.

I cannot provided pictures of the gear, bearings and oil report as this page/site will not allow it. If you want to see them email me at [email protected]

Mercury would not allow a warranty claim because it was over the 12 month period yet 50 hours under the warranty time.

I was informed by the mechanics that this is the first Bravo 3 leg to break like this in the world {my claim to fame :eek:} and this information came from mercury.

They replaced the whole top box at a reduced price {am I so lucky ?}, so I started research and found that only two things can cause it to break, misalignment or overheating.

So what I am asking here is this:
1/ Can constant overheating {139 to 140C/ 282F to 287F} for 450 hours be the cause of the main drive gear to break.
2/ Has there been any mercruiser 320 hp diesel inboard motors with a Bravo 3x leg broken a gear or overheated {mercury said at first, only 600 hp overheat then have reduced it to 360 hp and never has a 320 hp with Bravo 3 leg}
3/ Mercury claim it is a worlds first yet did not want to inspect the gears or take them to test, why?
4/ Does anyone know of this happening or can give expert reasons as to why the gear broke.
 
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