Yes, it is toast. Even if fixed, the chance of it breaking off and destroying the entire engine is too great. Watch eBay. You will find a decent replacement if not in a great hurry.
Most I've seen cracked were dropped. Otherwise, it may have been overly worn and piston slap - hard to say. Of course, since cast iron could be just "S" happens.
On the other hand, if you can clean both bores on +20, the barrel has a lot of life yet. As Greg noted, "s..." happens.
Did you measure the bore taper?Thanks for t he reply's guys.
I almost got excited today as I was going to one of my tickle trunks of new parts and I came across some new std rings.. the replacement jugs cleaned up nice and the std pistons fit nice then I went to measure them and I had 6 thou piston to wall clearance..
Too much in my books
Oops! 850. So, the factory bore was 3.0315 to 3.0325 Pistons, bottom of skirt: 3.028 to 3.0271 So it sounds like the pistons are undersized and the bore is oversized.
Let go back to the feeler guage. With the piston in the cylinder with the wrist pin side to side and the skirt even with the bottom of the bore. What is the gap between the skirt and bore measuring in front or back.
