Chainsaw Repair

 I have 2 questions:

 The first is what is the proper end ring gap for a stihl 025 with both the smaller 42mm and larger 42.5mm piston? I have both sizes. The ports on the head are different on the two. I'm wondering if this is an easy way for people to tell the difference in the piston size without a caliper or micrometer.

 The smaller of the two has "Mahle" cast into the side and a single transfer port on each side. The larger has a code ,"BR" on mine (I guess Brazil), and two ports on each side (or a large one with a divider longitudinally).

 The second question is how does one know when there's too much scoring in a cylinder to reuse it?

 My larger cylinder has a lot of scoring. Both exhaust and intake, though more exhaust. I used muriatic acid on it and it dissolved some aluminum. I began getting green on the Qtip, so I imagine it actually started eating into the nickel plate. I can feel the scoring with my finger tip. The piston and rings are scored as well.

 The funny thing is that this larger cylinder had 150 psi of compression despite this before disassembly. The less scored smaller one had 90 psi and a nearly new looking piston.

 Please let me know your thoughts and sorry for the long winded question.
 
 

Beyond the acid you have to