I can now join "MM" to the elite select group of folks who have managed to punch a hole in their 460 while trying to repair them. Months ago I posted about cosmetically rebuilding my 460. It was the "Old ammo deal 440" if you remember that story. Tore it all down except the cylinder (had plenty of compression and the piston looked good through the exhaust port), evaluated everything, cleaned it all up, replaced/painted some parts, and its been sitting in the basement since.................. never tried to start it till 2 weeks ago. It wouldn't start after trying all the tricks ................ had plenty of spark ................. would just flood out if you kept on pulling. Started to realize that it didn't seem to have the compression that it used to............... this was a 460, and I was pulling way too easy. After fooling with this saw for hours, I was convinced that there was nothing else wrong with it other than it seemed to have lost significant compression. I decided to tear it apart again and pull the cylinder this time, figured maybe a ring had cracked or something. When I pulled the carb off, gas sprayed out of the tank/hose under serious pressure all over the place. **** I was seriously pressurizing the gas tank somehow by pulling on it trying to start it, figured crankcase pressure through the impulse line to the carb/tank - ?***** To my surprise I found the following: What the _ _ _ _ ! I was stunned, no wonder I was loosing compression and it wouldn't fire . Then I remembered that I had removed the sprocket and clutch off the saw to clean them, using my piston stop tool to help get the clutch off. I have used the tool to remove clutches 2 dozen times now and never had a problem. I had always figured they could damage the piston with too much force, versus using the old rope technique. I rememberd that I had a heck of a time getting that old 460's clutch to break free .................. now I can see the force it took to finally "break it" .................. Oh well, already replaced the piston and have it all rebuilt and running fine, rebuilt the carb while I was at it too. I'm modifying the muffler at this point. Chalk it up to experience. I suppose this warrants a reconsideration of the use of metal piston stop tools versus the rope technique. I stopped using rope after having some rope fibers shave off inside and jamb in the ports/rings. Rope seems to easily get wedged onto "sharp" port openings. After this, I think I will keep using my metal tool carefully on the first attempt............... but if a clutch won't give and break free after "MODEST" effort I'll switch to rope and have at it. Most important of all, a good simple visual inspection of the piston through the spark plug hole when you're finished would have revealed the problem. I had that plug on and off a dozen times and never took a good look at the top of the piston .