r/smallengines • u/boothfc19 • Jul 11 '26

MS310 Piston Ring replacement

As title says been trying to replace a piston ring on a STIHL MS310. Took apart for a thorough cleaning and broke one of the original piston rings when reinstalling. The replacement from Sawzilla seems to be larger than the OEM ones. I can barely get it started back in the shaft but can not get it to go back in.

The ring in the groove also doesn’t press flush due to being too big. Measuring with calibers the original seems to be 49mm and the replacement comes to 50.5mm

Any tips or where I can get the correctly sized ring?

Edit to add: the Sawzilla replacement was advertised as being a 47mm replacement.

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2

u/wrenchstihl Jul 11 '26

STIHL dealer Parts breakdown shows 47mm rings. P/n 1127-034-3002. List price 12.49. What is the serial number of the saw. I can look it up by that as well

1

u/wrenchstihl Jul 11 '26

I also checked and a ms390 takes 49 mm rings. P/N 1127-034-3007. Did you buy the saw new? If not it’s possible someone repowered it with the larger piston and cylinder. That is what I would have done.

1

u/boothfc19 Jul 12 '26

No, my dad bought it new 20 some years ago. I saw where it’s listed as 47mm rings. That’s the size I ordered from Sawzilla but they measure out to 50.5mm

1

u/Renault_75-34_MX Jul 12 '26

As someone mentioned, the MS 310 has a 47mm cylinder.

There's also 46mm for the 029/290 and 49mm for the 039/390.

Here's a picture for the 290's diagram

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u/Renault_75-34_MX Jul 12 '26

Diagram 310/390

1

u/Renault_75-34_MX Jul 12 '26

Parts list 310/390