I have a 1950 Sears and Roebuck lawn mower in great condition and runs great also. It has a 3 1/2 horsepower engine with wind up cranking with release lever. I am curious of its value?

People collect all sorts of stuff. Maybe you can find someone who collects mowers. As a tool it has no value other than maybe $5 scrap. I hasd one of those back in the day. Is the winding handle white and folds down to let the spring fly? http://yetmans.mb.ca/antiques.html

Used one myself.

I would go to an old style lawn mower shop and maybe there's a collector/buff to tell you.

One test would be E Bay with a reserved bid.

I used one when I was a kid. I hated it. Cranked it didn't start, Cranked it almost started. Crank it again, Gave up!!