Author Topic: Stihl 025 Ring Gap and Scoring  (Read 226 times)

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Offline Drf255

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Stihl 025 Ring Gap and Scoring
« on: November 03, 2014, 07:56:12 am »


 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.
 
 

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Offline 660magnum

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Offline 660magnum

  • Global Moderator
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We should share what we know... someone may learn...
That knowledge can live after us... and that "Pays It Forward".
Be all that you can be . . .

Offline Drf255

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Re: Stihl 025 Ring Gap and Scoring
« Reply #3 on: November 12, 2014, 05:15:29 am »
The rings I bought from a USA seller are made in China, like everything else now. 

The gap is around .006. 

The cylinder polished up quite nicely with scotchbrite on a drill. 

Guess I'll open the gap to .010 with a fine file. 

 

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