MS460 Piston & Cylinder eater, any ideas?

[motohed]

 I have read most of the posts here . I have professionally  rebuilt , ported , hot saws etc . The first thing I would is check the connecting rod   lateral play  . Then I would check the rod play by really just trying to feel  what the rod bearing is doing . It should be smooth when rotated , you should not be able to flex the rod side ways . Don't confuse this with lateral play . Check the crank for lateral play in the cases , if all is good . spend the money or figure out how to pressure  test the cases  for at least an hour  . I would not more than a 2 psi drop you will be wasting money . If all is Ok you need to move on and find the air leak , I would expect at this point being a stihl that the pulse line or carb boot are leaking , so buy oem parts . Now If  you have already replaced these parts , there is a little known secret that all the body mounts are shot in your saw , so if you check your powerhead with the tank and handle setup  and have excessive play , maybe even wear on the power head this is your original problem . Ok guys another little peace of valuable information ,if your saw for no apperrant reason star running lean ,even if it's new check all your mounts . Ok  why because we loggers at some point get the saw stuck ,we rip we pull we have even bent the handle on the saw . we don't think about those new antivibe mounts we all love ! Truth is they are fragile and after we have pull we have slid the carb or pulse line out enough to leak air . The rest is easy put everything back  not much to it .  One thing I do is pressure test again over night , if it drops 5 psi , I would still be suspect , run it  , listen  for that lean run sound ,extra rpm here is not your friend stop ! The saw needs help ! I know to much time right . Well  what's it worth to not pay extra or worse lose another 2 days ! 8)
I want to say that I make this post with the assumption that every one knows what they are doing in the rebuild .

[sd locke]

check for the ports to be chambered  at least a 15 to 20 degree angle on all ports and check for the right ring end gap.so that way the rings have a nice ramp effect to move on going past the ports

[sd locke]

it looks like to me the manufacture is not chamfering the ports good the rings on your old piston looks like they slightly popped out of the exhaust port and snagged so check the chamfering on the ports on a new clyinder before installing a new one