I've got a 2001 90hp Merc. 4-stroke with a nickel sized hole in the adaptor plate or exhaust plate that connects the yamaha powerhead to the drive shaft houseing. The exhaust quickly fills the engine compartment and snuffs the engine. I've tried a jb weld patch but it doesn't hold. Mercury basically won't take any responsibility for their poor design. The part is $200 plus I've got to pull the powerhead, oil pump, lower unit, and replace all associated seals. I would really like to avoid that. Access is reasonable with the footing cover removed. Any ideas? The adaptor plate is aluminum. Is welding or brazing a bad idea? What about heat transfer - warping and melting seals, blowing electronics etc? Help please!

Is that cast iron? If so good luck trying to repair that. I wonder of there is a cheap way to patch it with a small piece of metal and some very shallow sheet metal screws and some jb-weld. Kinda cheesy of a fix if you ask me, but if you don't want to spend the $200, it can't hurt. Take this with a grain of salt though

First what caused the hole? If thin or defective casting hold Merc's feet to fire and they may replace it. If material is ok around hole and you have access, you could drill it out larger,tap it and install a brass plug...