I have a Craftsman push rotary mower with a 6-hp Briggs engine. It was
bought in 1997. I use it to keep 3/4 acre mowed. It has been smooth
and quiet and gets a lot from a quart of gas.

A couple of weeks ago I noticed it knocked and shook when I started.
That seemed better the next day. (Maybe the oil was cooler.)

Yesterday it was knocking under a load (heavy grass). It reminded me of
the sound behind a machine gun. I checked the muffler.

I get a knock if I disconnect the plug and pull the starter. If I turn
it on its side and tug the blade, there doesn't seem to be slop in the
main bearings.

If I turn the blade to the top of the compression stroke and move it
back and forth a little, there's a knock. I guess it's the
connecting-rod bearing.

The owner's manual has a parts breakdown for the engine. There are no
connecting-rod bearings. I guess one simply replaces the connecting rod.

What's cheap and expedient? Will I suddenly wreck the engine if I keep
mowing? Will 30W oil help? Should I assume the wear is on the rod and
simply install a new one? Is it better to buy a new mower?