278-1. Sharpening the saw chainCAUTION: Before doing any work on the guidebar or chain, always switch off the engineand pull the plug cap off the spark plug (see8‑6 “Replacing the spark plug”). Always wearprotective gloves!(Fig. 59)The chain needs sharpening when:The sawdust produced when sawing damp wood looks likewood flour.The chain penetrates the wood only under great pressure.The cutting edge is visibly damaged.The saw is pulled to the left or right when sawing. This iscaused by uneven sharpening of the chain.Important: Sharpen frequently, but without removing toomuch metal!Generally, 2 or 3 strokes of the file will be enough.Have the chain resharpened at a service center when youhave already sharpened it yourself several times.Proper sharpening:CAUTION: Use only chains and guide bars designed forthis saw (see 11 “Extract from the spare parts list”)!(Fig. 60)All cutters must be of the same length (dimension a). Cutterswith different lengths result in rough running of the chain andcan cause cracks in the chain.The minimum cutter length: 3 mm. Do not resharpen the chainwhen the minimum cutter length has been reached; at thispoint, the chain must be replaced (see 11 “Extract from thespare parts list” and 8‑4 “Replacing the saw chain”).The depth of the cut is determined by the difference in heightbetween the depth limiter (round nose) and the cutting edge.The best results are obtained with a depth‑limiter depth of0.64 mm (.025”).CAUTION: Excessive depth increasesthe risk of kickback!(Fig. 61)The sharpening angle (α) must be identical for all cutters!30° for chain type 092 (91VG), 492 (91PX), 290 (90SG)The teeth will have the proper angle (ß) automatically if theproper round file is used.80° for chain type 092 (91VG), 492 (91PX)75° for chain type 290 (90SG)Different angles result in a roughly, irregularly running chain,increase wear and tear and cause chain beakage.Files and how to work with themUse a special saw chain round file for sharpening. Standardround files are unsuitable. See 11 “Extract from the spare partslist”.Type 092 (91VG), 492 (91PX): Saw chain round file, dia. 4.0 mmType 290 (90SG): Saw chain round file, dia. 4.5 mm.(Fig. 62)The file should cut only when pushed forwards (arrow). Lift thefile when leading it backwards.First sharpen the shortest cutter. The length of this cutter isthen the standard for all other cutters of the chain.New saw teeth must be filed to the exact same shape as theused teeth, including on their running surfaces.File depending on chain type (90° or 10° to the guide bar).(Fig. 63)A file holder makes file guidance easier. It is marked for thecorrect sharpening angle of:α = 25°α = 30°α = 35°(keep the marks parallel with the chain when filing, seeillustration) and limits the cut depth to the correct 4/5 of the filediameter. See 11 “Extract from the spare parts list”.(Fig. 64)After having sharpened the chain, the height of the depthlimiter must be checked by means of a chain gauge. See 11“Extract from the spare parts list”.Correct even the smallest excess height with a special flatfile (1). See 11 “Extract from the spare parts list”.Round off the front of the depth limiter (2).8-2. Cleaning the inside of the sprocket guardCAUTION: Before doing any work on the guide bar orchain, always switch off the engine and pull the plugcap off the spark plug (see 8‑6 “Replacing the spark plug”).Always wear protective gloves!CAUTION: Start the chain saw only after havingassembled it completely and inspected.(Fig. 65)Remove the sprocket guard (1) (see 7 “PUTTING INTOOPERATION” for the correct model) and clean out the interiorwith a brush.Remove the chain (2) and guide bar (3).NOTE:Make sure there are no residues or foreign matter remaining inthe oil guide groove (4) or on the chain tensioner (5).To install the guide bar, saw chain, and sprocket guard, see 7“PUTTING INTO OPERATION” for the correct model.NOTE:The chain brake is a very important safety device andlike any other component subject to normal wear andtear.Regular inspection and maintenance are important foryour own safety and must be done by a MAKITA servicecenter.SERVICE8. MAINTENANCE