The oil pump on a Stihl 180 chain saw operates the automatic chain lubrication. This pump draws oil from the tank and pushes it up into the bar, where it lubricates the spinning chain. The oil pump can get damaged in many ways or can get clogged from impurities in the oil. Repairing the oil pump requires removing and disassembling it, which, if you are unfamiliar with small engines, is better left to a qualified mechanic.
Take off the bar and chain cover. Unscrew the bar nut with the wrench. Lift the cover free and slide the bar and chain off its seat on the engine. Take off the top cylinder cover using the screwdriver to pop open the clips. Unfasten the rubber boot that's attached to the spark plug. Unscrew the spark plug with the socket wrench and socket.
Take the spark plug out and insert the piston block tool in its place. Pull out on the starter rope until the piston hits the stop tool. Drive off the retaining ring on the crankshaft stub using the tip of the screwdriver. Slide off the clutch's dust plate, the clutch drum, sprocket and needle cage.
Lift the metal washer, if present, off the top of the clutch. Bend the clutch springs free using the metal clutch hook. Pull each spring free and separate the clutch shoes from the clutch carrier. Remove the clutch carrier.
Lift the end of the drive spring up and pull out the drive spring and attached worm drive. Push the oil pump's bar hose off the pump housing with the flat tip of the screwdriver. Unscrew the two oil pump mounting screws. Lift the bottom of the pump forward a little and slowly lift the rear of the pump off the engine housing. Take the elbow connector off the engine housing with the pump.
Turn the elbow connector 90 degrees and pull it off the pump. Take the O-ring off the elbow connector. Use a 2mm drift to punch out the spring pin from the bottom of the pump. Pull the control belt out of the pump housing, which is on the bottom of the pump. Take off the two O-rings. Pull out the pump's piston from the other end of the pump, along with the washer and spring.
Clean all oil pump parts in the standard solvent based degreasant. Make sure the degreasant contains no chlorinated or halogenated hydrocarbons. Replace any worn parts, including dirty pistons, bent springs and oil pump housing. Install all parts in reverse sequence, making sure to use only new O-rings.
- Stihl MS 290, 310, 390 Service Manual; Andreas Stihl AG & Co.; 2004
- Stihl Official Site: MS 180 Information
- Draw a picture diagram of oil pump parts before you disassemble to help with the reassembly.