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Stripped Slot on Gearbox Drain Plug

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guitobache

New member
I have an older Yamaha 100hp outboard. When going to do the lower unit gear oil, I discovered the previous owner had completely buggered the screwdriver slot on the drain plug. As with everything else on this vessel, I can predict that the plug is "in there", and won't come out without a fight, even if the thread were pristine. Suggestions? I believe its brass
 
There are a few ways you can go here. There might be enough thread to use an screwdriver (the ones you hit with a hammer to both seat them and turn them at the same time). If that doesn't work I would drill a small hole through the centre of it and then use an Easyout to get a grip on it and wind it out. A bit of head on the casing my help get it out too. Don't heat the aluminium too much though. If that all fails you'll need to carefully drill the whole plug out and then use a tap to clean/ repair the thread.

Good luck!
Stuart
 
DangarStu said:
There are a few ways you can go here. There might be enough thread to use an screwdriver (the ones you hit with a hammer to both seat them and turn them at the same time). If that doesn't work I would drill a small hole through the centre of it and then use an Easyout to get a grip on it and wind it out. A bit of head on the casing my help get it out too. Don't heat the aluminium too much though. If that all fails you'll need to carefully drill the whole plug out and then use a tap to clean/ repair the thread.

Good luck!
Stuart
Click to expand...

Yeah, that's what I was afraid of. Of course, the re-tap HAS to be straight and true to enable a flat seating of the washer, I'm sure. You wouldn't happen to know off the top of your head the pitch and thread size of the plug? I'm going to try and recreate the slot with a die grinder and a small endmill first with a small amount of heat first. This boat has been sitting for a long period of time and is proving to be a real challenge. Rebuilt carbs and compression is good. Wiring is a nightmare. I though a quick fluid change would be a breeze. My mistake
 
This is exactly what I did. The plug is brass, so it basically just made more of a mess of it. I was able to recreate a better. deeper slot, and used a stout screwdriver and vise grips. The end result was a bent screw driver tip. I believe I'm screwed
 
guitobache said:
Yeah, that's what I was afraid of. Of course, the re-tap HAS to be straight and true to enable a flat seating of the washer, I'm sure. You wouldn't happen to know off the top of your head the pitch and thread size of the plug? I'm going to try and recreate the slot with a die grinder and a small endmill first with a small amount of heat first. This boat has been sitting for a long period of time and is proving to be a real challenge. Rebuilt carbs and compression is good. Wiring is a nightmare. I though a quick fluid change would be a breeze. My mistake
Click to expand...
I was advised not to drill the plug out, because the magnet would come off on the backside. Do brass plugs have magnets on them?
 
I'm not 100% sure if the brass plugs have magnets, but if it really easy so stuck they you bent a screwdriver trying to remove it them you might not have much choice other than to drill it out. Did you apply some head around the plug while you were trying to remove it? If you do end up needing to drill it out it will probably be best to remove the gears from the casing to allow you to flush any metal fragments out (including the magnet should it bear there and drop inside). This of course makes it an even bigger job. How simple those instructions sound, "Just remove the lower plug..." I know how you feel.
 
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