I put a salvaged engine in my wife's '97 Legacy Postal 2.2L. Since the old engine worked so well for 400,000 miles I'm trying to rebuild it so we'll have a spare. The bolts holding the halves of the block together have come out nicely but for the 12 point 12 mm bolts that have been washed in coolant for 16 years. I haven't applied full force to them with my long breaker bar because it seems that the bolt heads are likely to strip at some point. Then I would have to drill them out with a bit extension since they are recessed between the cylinders. I've soaked them in PB blaster for a couple of days, but since the block is aluminum and the bolts steel I understand that perhaps ammonia would be a more effective anti-corrosive. I guess I'll try that? Would the use of an impact wrench be more likely or less likely to strip the bolt heads than gradually increasing  torque with a breaker bar? By the way I'm surprised that the cylinder walls still have their full component of honing marks after all those miles.

Use a good fitting 12 point.

 

I preffer a 3/8 drive to a 1/2" because it's smaller profile.  A big fat 1/2" socket can jam against the outside of the cylinder wall and exert undo pressure sideways against the lip.  Espescially on 2.5 but still on 2.2 it's tight.

 

Can't emphasize enough though how you need a good 12 point, seated fully. Then give 'er a go.  They'll pop loose.

Thanks. I'll pick up a "fresh" socket at Sears.