Crack in outboard gearbox casing - should I be worried?

[sail&fish]

I went to change the gearbox oil today in my Yamaha 25 autolube serial number 25 NMO 6L2 L 401779 [F].

On inspection I saw 2 cracks at the prop end of the gearbox casing and another crack on the opposite side. The cracks are shown in the photos and appear to have been caused at some time by somebody removing the end off the gearbox. The longest crack is about 2 cm long and the metal is lifted very slightly (0.5mm) at the end between the 2 cracks.

I was expecting the gearbox to be dry and thinking myself lucky as I had used the engine last month with no problems. However there was plenty of oil in the gearbox, no water and the oil was not emulsified.

The engine is about 18 years old and I have owned and used it for a year, during which time I have not run it aground or hit anything.

So should I be worried?

• Is this just a piece of housing that does not seal in the oil?
• Is it structural and therefore likely to cause a failure?
• Do I continue to use and monitor for any crack growth?

Many thanks

 

[rodbolt]

Re: Crack in outboard gearbox casing - should I be worried?

the oil sealing oring is another 3 or 4 inches down.
drill a 1/8th hole at the end of the crack to slow it down. the cracking is due to corrosion building up between the bearing carrier and the housing.
if you try to weld it remove the carrier, machine a plug to fit that part of the bore and have it welded, without a plug its possible to distort the bore.
but its fairly common in salt water or high mineral content waters.
only way to prevent it is to remove and clean the carrier and bore every few years.
but no its not a structual issue will most likly go a long time but one day, like everything, it will fail.

 

[Ray Neudecker]

Re: Crack in outboard gearbox casing - should I be worried?

As Rodbolt says sooner or later it will fail and spit the propshaft, prop, ect out into the water.
I would be looking now for a used freshwater housing, while the other parts are still usable. Any thing else is only a very temporary solution.