My old 1982 Murray had an engine (Briggs Aluminum 11hp vertical)
lockup today. The oil was full and fresh (having been changed last
weekend) and the aircleaner in place and clean.

What caused it beats the hell out of me but I'm at a point where I
need to make a decision as to what to do now.

Could I get by with using a smaller replacement engine? How about an
8hp instead of the 11hp?

Another option is to bore the cylinder, getter a larger piston, new
rings, etc. Right now the engine will not turn over and I can't turn
it by hand which usually I've been able to do. I figure I'll have to
use a sledgehammer to get the old piston out. But is it possible that
I may still be able to use the crankshaft? Surely the piston is gone
and probably the rod but I'm hoping that the main crankshaft is
useable.

Then there's the option of getting a new 11 or 12 HP Briggs engine.
One I was has the recoil type shroud along with the electric starter
motor. If I spend money on this engine am I likely to see my
transaxle die next?

Thanks for all replies.