Stihl MS311 / MS391 Rebuild Center
The Stihl MS311 and MS391 are the same 1140 series saw in two bore sizes. This page covers which saw takes which piston or cylinder, the part numbers our kits replace, and the checks that stop a wrong order.
At a glance
| Saws | Stihl MS311 · MS391 |
|---|---|
| Bore and displacement | MS311: 47mm, 59.0cc MS391: 49mm, 64.1cc Both use a 34mm stroke |
| MS311 piston | Replaces 1140-030-2002 (superseded to 1140-030-2009) |
| MS391 piston | Replaces 1140-030-2003 (superseded to 1140-030-2008) |
| Piston styles | Standard flat top · Pop-up (raised dome, higher compression) |
| Cylinder kits | 49mm Nikasil cylinder and piston, 3-bolt intake, replaces 1140-020-1204 MS391: straight replacement at stock bore MS311: big bore conversion from 47mm to 49mm |
| Piston kits include | Piston, ring, wrist pin and circlips. Cylinder, needle bearing, gaskets and crank seals are not included. |
| Not these saws | MS310 (1127 series, piston 1127-030-2007) · 039 and MS390 (piston 1127-030-2005) |
Check these four things before you order
- The model on the saw. The MS311 and MS310 are both 47mm and 59cc but take different parts. The MS391 and MS390 are both 49mm and 64.1cc but take different pistons. Measuring the bore will not tell them apart. Read the model plate. Where to find the tag
- Bore size on an MS311. A stock MS311 is 47mm. If someone has fitted a 49mm big bore cylinder, the 47mm piston is the wrong part. Measure the bore if you did not build the saw yourself.
- Intake bolts (cylinder kits). These cylinders were made with 3-bolt and 4-bolt intakes. Our cylinder kits are the 3-bolt version and do not fit a 4-bolt saw. Count the bolts holding the intake to your old cylinder.
- Squish clearance (pop-up pistons). The raised dome uses up squish clearance. Check it with a solder test through the plug hole and set base gasket thickness from what you measure. Do not combine a pop-up with a base gasket delete.
Which kit do I need?
- Scored piston, cylinder is clean: a standard piston kit at your stock bore, 47mm for the MS311 or 49mm for the MS391. Look through the exhaust port first. A new piston in a damaged cylinder is wasted.
- More compression, same cylinder: the pop-up piston kit for your saw. Measure squish on assembly and set the high-speed mixture a little rich for the first tank.
- MS391 cylinder is damaged: the 49mm Nikasil cylinder and piston kit (3-bolt intake).
- MS311, want more displacement: the 49mm big bore cylinder and piston kit (3-bolt intake). It changes the bore, so check the carburetor setting once the saw is run in.
- Whatever you fit: pressure and vacuum test the crankcase and check the crank seals, intake boot and impulse line. An air leak will score a new piston as fast as the old one.
More on measuring before you order: Measure before ordering rings and pistons.