How was it ever running?

[ricky racer]

I would definitely bore it to .020, purchase the correct .020 over pistons and rings. That way you know it is done right and good for another 1000 hours.

More like good for another 60 years....

[Clark Thompson]

I have rebuilt hundreds of cub engines. There was a day that you could go by the bore specks in the book but not these days. If it needs bored to .020 over then I would suggest getting a .030 piston kit. ( aluminum pistons ). Get the kit then take the block and piston kit to the machine shop. They will be able to bore to proper size. Remember there are a bunch of companies manufacturing pistons. They do NOT pay particular attention to bore specks. For instance say you bought a kit from a company that says they are .030 oversize and you already had your cylinders bored to .030. They actually may be .033 over and will not fit. So its a good idea to have your new pistons on hand so the machine shop can properly fit them. Cast iron pistons only require .002 clearance wile aluminum requires .003 to .004.

[ricky racer]

Very good advice....