I have a 1990 Craftsman 12 hp Briggs 38 in lawn tractor that has just developed a bad engine knock on starting, and sometimes at shutoff. Knocking goes away once running up to speed, and it seems to run smooth, with good power. Oil level is up, etc.
What's the problem, is it a major engine repair, at what estimated cost for this old mower with a rusty deck? What risk in just continuing to use it as is? Will it do major damage that makes it not worth fixing? Anything minor that would help, such as oil additives?
Thanks.
Hubert

No Probably Not What You Want To Hear, But This Could Be A Connecting Rod Problem, You Say It Is At Start Up And Shut Down At Low Rpms, Perhaps You Should Just Run It Until It Throws The Rod, And Replace The Engine, Or Replace The Whole Mower. Don't Let Someone Talk You Into Rebuilding The Engine. They Seem To Have A Very Short Life After Rebuilds. You May Buy A Used Engine.

Check for carbon build up on top of piston

Well hubert, what are the results?