[sww914]

Many years as a mechanic on aircooled engines has taught me that 3 things get tough bolts out. Heat, impact (not torque), and juice. By juice I mean Wurth Rost Off, Kroil or PB Blaster. PB may be my favorite. If those fail I weld a nut on and impact it off. Welding and impact are much easier in my shop than they are on a boat.

 

[sww914]

My favorite obviously is a 1/2" drive air impact that does 600 ft lbs in reverse. That's difficult on a boat so probably a hammer driven impact driver will get the job done unless the heads are too stripped out, then you're down to a chisel if you can't get a nut migged on there. I've had to use the chisel on Porsche CV joint bolts lots of times and on flywheel bolts a couple of times. I start pounding the chisel straight into the axis of the bolt to build a bit of a shelf to hit on later. After I've formed something to hit with the chisel I'll start moving it so that I'm striking parallel to the axis of the bolt in the direction that will begin to unscrew the bolt. As long as you have access to the side of the bolt head and enough room to swing a hammer this will usually work. The last resort would be to drill the head off of the offending bolt(s) to get the flywheel out of the way. I've only needed to drill out 2 bolts in the last several years.