Mercury 3.3 ioutboard: gearbox removal

[Two Sheds]

I have posted before about my woes with this. To recap, there is some kind of obstruction in the gearbox such that the vent hole doesn't vent and it is impossible to refill with gear oil. So I decided to take the gearbox off to investigate. I have a manual so followed the instructions to disconnect the gearchange rod,remove the two retaining bolts and drop the box from the leg. Perhaps not surprisingly (it is quite an old engine and the box has not been off before) the heads of each of the bolts sheared off. Theoretically that shouldn't matter, but the gearbox wouldn't move, presumably due to corrosion on the bolts/threads and at the join between the gearbox and the leg. So I have been treating both bolts and join with a mixture of ATF and acetone, day and night for three weeks. Still no joy despite much judicious bashing with wooden mallet and a bit of injudicious bashing with metal drift and hammer that has damaged the fins. I have also tried several cycles of heating up (blowtorch) and cooling.

Anyone any ideas? I have run out of them myself.
Thanks all
Martin

 

[alahol2]

Can you not get into the gearbox by removing the plate behind the propellor?

 

[Two Sheds]

Yes I could, but having now sheared off the gearbox retaining bolts I have to get the gearbox off to replace them!

Martin

 

[Heckler]

Yes I could, but having now sheared off the gearbox retaining bolts I have to get the gearbox off to replace them!

Martin

Its a case of "werrying" the stupid things, bashing, tapping, feeing oil and eventually it will come apart.
Stu

 

[neale]

Got the T shirt on this one. I ended up drilling the stainless bolts out and only then would the lower leg separate. Unbelievably it was simply the corrosion on the bolt shafts as they go through the aluminium that was holding it on but absolutley nothing would shift it.

 

[JustMelfort]

Never tried it myself but I've heard good reports of soaking corroded bolts in Coke to loosen them. This may work best on rust rather than the corroded joints in your case, but it may be worth a go. Just google it. Or mix it with rum to ease the frustration.

 

[Two Sheds]

Thanks all. Just as I suspected, there is no silver bullet for this one and it is a case of seeking to be patient with the penetrating oil/coke etc. and trying to contain the urge to bash it to bits with the biggest hammer I can find!

But I'll have a go at drilling the bolts out. Won't be easy as they're stainless, but might work.

Martin

 

[misterg]

If the remains of the bolts are accessible you can weld a length of bar to them and use that to ease them to and fro. The intense heat from welding will break the grip from the corrosion - works a treat on japanese motorbike aluminium castings with steel bolts.

0.02p

Andy