Duane Bozarth wrote:

Choreboy wrote:

....
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?

A) Cheap and expedient is to run it until it dies and replace it or at
least the motor.
B) Yes
C) For a very short additional time, maybe
D) No--the rod and crank will both be gone by now
E) Probably at least the engine--repair parts are normally nearly the
price of the whole engine--it is worth looking at if you're able to do a
competent repair yourself, but it's likely the cylinder walls are worn
by this time anyway, as well as who knows what else...

A neighbor said in his experience there may be no wear on a steel
crankshaft when an aluminum connecting rod wears out. A cousin said he
had filed a connecting-rod cap to take up connecting-rod slack, and the
Briggs engine had run fine for years afterward.

So I took the pan off. I could find no slack in the connecting rod.
Everything looked amazingly clean and unworn. The clicking with the
ignition off had come from backlash in the camshaft gear. It didn't
look worn, so the backlash may have been correct.

Still not knowing the cause of the knocking, I removed the head. The
valves seemed okay. I noticed the cam opened the exhaust valve very
slightly for a moment during the compression stroke. Could that be a
sort of compression release for starting?

Deposits can cause knocking, so I scraped away the slight deposits. I
replaced the air filter. Now it mulches fairly heavy growth at an idle
with only faint knocking.

It makes me wonder. Are modern mower engines made to knock a little for
reduced hydrocarbon emissions? Could a clogged air filter cause worse knocking?