Piston Kit Stihl MS400 MS400C 50mm 1140-030-2014 Standard

Standard piston kit for the Stihl MS 400 C-M. 50mm bore. Replaces 1140-030-2014. STANDARD OR POP UP - WHICH PAGE YOU WANT This page is the STANDARD flat top piston. It returns the saw to factory compression, runs on the same fuel mix the saw already uses, and needs nothing measured or machined. This is the right part for a scored or seized piston or any repair where you want the saw back as it was. We also sell a POP UP piston for this saw. That one has a raised crown that reduces combustion chamber volume and raises compression. It is for someone already into the cylinder - porting, cutting the base, or reworking the squish band - who will measure squish clearance before final assembly. It is not a drop in power upgrade. If you are repairing rather than building, you want this page. IMPORTANT - MS400 IS NOT MS 400.1 The MS 400 C-M is 66.8cc. The MS 400.1 C-M, which replaced it, is 62.6cc. Those are different engines with different bores, and this 50mm piston does not fit the 400.1. Read the model plate on your saw. If it says 400.1, this is not your piston. SPECIFICATION Bore - 50mm Displacement - 66.8cc, 4.1 cubic inches Engine - two mix stratified charge, M-Tronic MS400 AND MS400C ARE THE SAME SAW. Stihl's full designation is MS 400 C-M. The C is comfort features and the M is M-Tronic - neither is an engine difference. Whichever way your saw is badged, this is the piston. RELATED NUMBERS 1140-030-2014 - piston, 50mm, supplied here 1140-034-3010 - piston ring, 50 by 1.2mm 1140-007-1014 - piston pin set with needle cage 1140-020-1212 - complete cylinder with piston, if the bore is damaged as well ALUMINIUM REPRODUCTION The factory piston in this saw is magnesium - Stihl made a feature of it. This is an aluminium reproduction piston, which is slightly heavier than the original. It is a repair part that gets a saw back to work. We are telling you up front rather than describing it as a factory piston, because it is not one. BEFORE YOU ASSEMBLE Find out why the old one failed. Scoring on the exhaust side is lean running or an air leak, and a new piston in the same conditions will score too. Pressure and vacuum test the crankcase. On a strato engine this matters even more, because there are more ways for it to leak. Check the intake boot for cracks and both crankshaft seals for hardness. Clean both base gasket faces back to bare metal. Check the ring end gap in the bore and make sure the ring is free in its groove. Fit the circlips with the opening away from the ports and check both are fully seated. On an M-Tronic saw, let the machine relearn after a rebuild before you judge how it runs.

• STANDARD FLAT TOP - THE ONE FOR A STRAIGHT REPAIR - This is the standard replacement piston. It keeps factory compression, goes in with nothing to measure, and runs on the same fuel mix the saw already uses - no hunting for higher octane the way a raised compression build wants. If your saw scored or seized, this is the part. We also sell a pop up version, but that is for someone already working the cylinder who will measure squish clearance first - not a bolt in upgrade for a stock work saw.
• DOES NOT FIT THE MS 400.1 - THE NEWER SAW IS A DIFFERENT ENGINE - The MS 400 C-M is 66.8cc. The MS 400.1 C-M that replaced it is 62.6cc, which is a different bore, and this piston will not fit it. If your saw's plate reads 400.1, this is the wrong part. This catches people out because both saws are called a 400.
• FITS MS400 AND MS400C - 50mm bore, 66.8cc. Replaces 1140-030-2014 and pairs with cylinder 1140-020-1212. Ring is 50 by 1.2mm, 1140-034-3010, and the pin set with cage is 1140-007-1014. MS400 and MS400C are the same saw written two ways - the C is comfort features, not a different engine, so both take this piston.
• ALUMINIUM REPRODUCTION PISTON - WHAT THAT MEANS - The original factory piston in this saw is magnesium, which is unusual and is one of the things the saw was sold on. This is an aluminium reproduction, so it is slightly heavier than the original. It does the job of getting a saw back to work, and that is what it is for. We would rather tell you that than let you find out.
• IT IS A STRATO ENGINE - BUILD IT CLEAN - This saw uses the two mix stratified charge system, so there are extra passages in the cylinder feeding air over the piston. Scoring here is almost always lean running or an air leak. Pressure and vacuum test the crankcase, check the intake boot and both crank seals, and clean the base gasket faces properly. Fit the circlips with the opening away from the ports and check ring end gap in the bore before you close it up.