Gogarty wrote:
Will PB Blaster free a stainless steel bolt frozen in an aluminum
casting? Will anything loosen such a bolt in such a casting? Serious
question. My bow fitting is aluminum secured to the boat with a stainless
steel chainplate. But the bolt that holds the forestay in place is
stainless steel inserted through ears on the casting. And it's frozen.

You have one of those situations that everyone dreads. The safest way to
solve it is the most agressive. If you're uncomfortable about drilling
it out yourself, have a millwright or machinist do it for you. Trust me
it is the solution with the least risk.
If you are going to do it yourself use a center punch to strick a pilot
indentation dead center of the bolt. This will keep your drill bit from
traveling off center when you start drilling and assist in drilling
through the bolt dead center. Extreme care needs to be taken to keep the
drill bit in line with the bolt and not drift off at an angle. Use a
much smaller drill bit than what is needed to chase the bolt to the
thread size first as a pilot hole . Then increase to the size of drill
bit needed to actually drill out the bolt. Your dealing with stainless
steal, take care not to have the drill brake off. A broken bit will be
worse than the situation you have now. Once the hole has been drilled
out to the bolt size just at the threads you can then decide to chase
the threads with a tap of the same thread size or drill to the reomended
hole size to accept the next size tap to the next bolt size. Using heat
will undoubtably compromise the aluminum. You don't want to go there. If
you decide to use chemicles to lossen the bolt, center punch it first to
be sure you have dead center before trying to remove the bolt because
once you try removeing the bolt you will deform the outside edges making
it difficult to find center afterwards for drilling. Even using
chemicals you will need to strike the bolt several times to break the
aluminum oxide that has frozen the bolt. Spray with chemical hit bolt
using hammer and center punch spray chemical and strike again. Let stand
for a period of time then repeat. You may want to spread this process
over the entire day to let the chemical have a chance to actually
penitrate. haste makes waste. Sorry for the wandering thought. I've A
horrible headache.
Hope this helps.
Good Luck