How Did My Gear Box Blow Itself Up?

[subzero]

G'day Raiders,

I've been rebuilding a 4.4m Stejcraft fibreglass runabout for about 18 months now and I am/was looking forward to getting it out on the water for the first time at Xmas time. The motor on the back is a 1980 Mariner 60Hp. I've replaced the leg on the motor due to the main bracket being seized and corrosion on the bolts which secure the bracket and the motor to the leg. I picked up another complete motor off ebay for $150 which apparently the only problem with it is its letting water into on of the pistons. So I have a few spare parts. All the work has been done by myself and my father-in-law.

Today I was running the motor just to give it a run because it hasn't been run for quite a while. I put it in gear for a couple of minutes when a really bad sounding screech was coming from the motor. I quickly killed the ignition. I could smell oil which was not a good sign. Further investigation revealed that a hole had been blown out the side of the gear box. I am at a loss to explain why it happened because we ran it a couple of months ago when we first put it back together. The only time we did anything to the gear box was when we changed the oil and replaced the impeller.

So now we are going to have to use the spare gear box that I have. Any info as to why this could happen would be greatly appreciated. Can it be repaired? I've posted a pic so you can all see the damage.

Cheers.

[johnno]

I am not a mechanic

but

possibly it broke a tooth off a gear inside and that helped punch the holes

Did you follow the correct way that is recommended to change the oil

as i know my mercury has a set way it needs to be refilled.

Why where you running it in gear out off the water

i have never done this. It may also have had something to do with it.

[subzero]

I am not a mechanic

but

possibly it broke a tooth off a gear inside and that helped punch the holes

Did you follow the correct way that is recommended to change the oil

as i know my mercury has a set way it needs to be refilled.

Why where you running it in gear out off the water

i have never done this. It may also have had something to do with it.

Yeah I followed the correct procedure out of the manual to change the oil.

I was running it in gear to check that I had positioned the gear shift lever correctly

when we refitted the gear box to the leg.

This whole boat rebuild has been a learning experience, so I guess this is another.