stihl 025

[chris ham]

Just got around to this one again.I replaced the piston and rings with a new golf kit.Piston and cylinder that were in it looked good.The compression dropped from 130 to 100 with the new kit.The old piston measured 41.90.I replaced with 42 millimeter kit.I pressure and vacume tested,no leaks.Everything appears to be in order, will not fire up.Any suggestions.Just about ready to give up on this one.

 

[dougand3]

If original piston looked good...still see some horizontal machine marks and no scoring, I'd try just a new Caber ring.

 

[walterg]

Chris, did you check the ring end gap on the new rings?

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[chris ham]

how do you check ring end gap

 

[walterg]

Put the new rings in the bore and push them down a little. Usually with the piston. You can measure the ring end gap with feeler gauges.
I've seen new AM rings that had almost zero gap to way to large a gap.

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[chris ham]

what would be the right ring gap

 

[walterg]

Have too look it up in the service manual. I will Post back later.

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[walterg]

Not in the service manual. Very strange. I believe 7 to 10 thou is the average.
Someone else can jump in if they know for sure.

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[chris ham]

I will take it back down and check

 

[TheTone]

I've heard .004-.006 per inch of bore diameter. The 025 bore is 1.65", so that would be about .007-.010 for new rings.

 

[HarleyT]

The manuals don't give a ring gap.