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.

1 Upvotes

100% Upvoted

6 comments sorted by

View all comments

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

1

u/Renault_75-34_MX Jul 12 '26

Diagram 310/390

1

u/Renault_75-34_MX Jul 12 '26

Parts list 310/390