done and dusted.

 

id start looking for a whole new motor...but thats just me

 

doesn't seem too bad- pretty sure itll be fine.

 

Looks like it may be salvageable. Get some sandpaper and go to at it. I'd recheck the combustion chamber volume after, but even knocking those rough spots down you shouldn't be changing it much. I'd also check my valve to pistion distance and look very closely at the valve angle radii (radiuses?) for defects.

 

piston checked, all good.

 

cylinder wall condition is going to be your biggest concern.

Likely had a loose spark plug, cylinder leaned out and melted the electrode off, and dance in there for a while.

I can guarantee whoever sold you the motor knew of the problem.

Do you see an unusual amount of soot in the #4 spark plug tube?

I'm confident your crank and rod will be ok. Piston not so sure. There's plenty of used pistons around to be had...A or B piston?

 

all been checked and fine. no damage.

 

The plug tip on your plugs will be fine...this happened before you got the engine. The engine was like that when you bought it. I'd be very pissed at the seller.

A-B can be in ap1 or ap2. the pistons will have a letter on top, a or b. there will also be AAAA or BBBB on the block. Or possible ABBA.

Machine shop can tell you about the head.

That is not detonation. This happened be a piece of solid metal, most likely a spark plug tip, from a loose plug.

 

all checked out- must have been luckily I caught it sooner.