Stihl Ht 75 Owners Manual
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30 english HT 70, HT 75Standard Setting:Shut off the engine. :Check chain tension. :Check the air filter and clean or replace as necessary. :Check spark arresting screen* and clean or replace as necessary. :Check adjustment of the throttle cable and readjust if necessary – see Adjusting the Throttle Cable. :Turn high speed screw (H) counterclockwise (max. 3/4 turn) as far as stop. :Carefully screw the low speed screw (L) down onto its seat. Then open it one turn counterclockwise. :Start and warm up the engine. :Adjust idle speed with the idle speed screw (LA) so that the chain does not rotate.Fine Tuning A slight correction of the setting of the high speed screw (H) may be necessary if engine power is not satisfactory when operating at high altitude or at sea level. * see Guide to Using this Manual”Rule of thumb :Turn high speed screw (H) about 1/4 turn for every 1000m (3300 ft) change in altitude. Conditions for adjustment :Carry out standard setting. :Warm up engine for about 5 minutes. :Open the throttle wide. At high altitude :Turn high speed screw (H) clock- wise (leaner) no further than stop until there is no noticeable increase in engine speed. At sea level :Turn high speed screw (H) counter- clockwise (richer) no further than stop until there is no noticeable increase in engine speed. It is possible that maximum engine speed may be reached with the standard setting in each case. Adjusting Idle SpeedIt is usually necessary to change the setting of the idle speed screw (LA) after every correction to the low speed screw (L). :Warm up engine for about 5 minutes. Engine stops while idling :Turn idle speed screw (LA) slowly clockwise until the engine runs smoothly – chain must not rotate. Chain rotates when engine is idling :Turn idle speed screw (LA) slowly counterclockwise until chain stops rotating and then turn the screw about another 1/2 to 1 turn in the same direction. Erratic idling behavior, engine stops even though setting of LA screw is correct, poor acceleration Idle setting too lean: :Turn low speed screw (L) counterclockwise (about 1/4 turn) until the engine runs and accelerates smoothly.
31 HT 70, HT 75english Erratic idling behavior Idle setting too rich: :Turn low speed screw (L) clockwise (about 1/4 turn) until the engine runs and accelerates smoothly. If the engine is low on power, check the spark arresting screen in the muffler. :Lift spark arresting screen and pull it out sideways. :Clean spark arresting screen if necessary. :If screen is damaged or coked up, fit a new one. :Refit the spark arresting screen. * see “Guide to Using this Manual”Wrong fuel mix (too much engine oil in the gasoline), a dirty air filter and unfavorable running conditions (mostly at part throttle etc.) affect the condition of the spark plug. These factors cause deposits to form on the insulator nose which may result in trouble in operation. Spark Arresting Screen* in Muffler 392BA035 KN Checking the Spark Plug 000BA002 KN
32 english HT 70, HT 75 If engine is down on power, difficult to start or runs poorly at idling speed, first check the spark plug. :Remove spark plug - see “Starting / Stopping the Engine“. :Clean dirty spark plug. :Check electrode gap (A) and readjust if necessary – see Specifications. :Use only resistor type spark plugs of the approved range. Rectify problems which have caused fouling of spark plug: :Too much oil in fuel mix. :Dirty air filter. :Unfavorable running conditions, e.g. operating at part load. Fit a new spark plug after approx. 100 operating hours or earlier if the electrodes are badly eroded.To reduce the risk of fire and burn injury, use only spark plugs authorized by STIHL. Always press spark plug boot (2) snugly onto spark plug terminal (1) of the proper size. (Note: If boot has detachable SAE adapter nut, it must be attached.) A loose connection between spark plug boot and ignition wire connector in the boot may create arcing that could ignite combustible fumes and cause a fire. Removing the Starter Cover:Take out the screws (1). :Remove the cable lug, if fitted. :Lift the starter cover (2) away from the tank (3) and pull it out from under the shroud (4). 000BA036 TR 1 Replacing the Starter Rope and Rewind Spring 386BA004 KN 1 1 12 34
33 HT 70, HT 75english Removing the Rope Rotor:Take out the screw (5). :Remove the rope rotor very carefully. The rewind spring is seated in the rope rotor and may pop out and uncoil if care is not taken. The pieces of broken spring may be under tension and fly apart unexpectedly when you remove the rope rotor. To help reduce the risk of injury, wear face protection and gloves. Replacing the Starter Rope:Use a screwdriver to pry the cap (6) out of the starter grip. :Remove remaining rope from the rotor and grip, making sure the ElastoStart sleeve is not pushed out of the grip. :Tie a simple overhand knot in the end of the new starter rope (see Specifications) and then thread the rope through the top of the grip and the rope bush (7). :Refit the cap in the grip.:Pull the rope through the rotor and secure it with a simple overhand knot. :Go to Installing the rope rotor. Replacing a Broken Rewind SpringTwo types of replacement spring are available from the factory: – A ready-to-fit rewind spring secured with a wire retainer. – A rope rotor with pre-installed rewind spring. Installing the ready-to-fit rewind spring :Lubricate the spring with a few drops of non-resinous oil – see Special Accessories – do not open the wire retainer! 5 392BA014 KN 67 392BA015 KN 392BA024 KN
34 english HT 70, HT 75 :Carefully remove the parts of the old spring from the starter cover and rope rotor. :Insert the new rewind spring in the rope rotor and, at the same time, engage the outer spring loop in the rotor’s recess – the wire retainer slips off in this process. If the spring pops out and uncoils, refit it in the counterclockwise direction, starting outside and working inwards. :Go to Installing the Rope Rotor. Installing rope rotor with rewind spring :Carefully unpack the new rope rotor with rewind spring. The spring may pop out if not handled with care – risk of injury. :Lubricate the spring with a few drops of non-resinous oil – see Special Accessories. :Go to Installing the Rope Rotor. Installing the Rope Rotor:Check dimension a for inner spring anchor loop and bend it slightly if necessary. :Coat rope rotor bearing bore with non-resinous oil – see Special Accessories. :Slide the rotor onto the starter post – turn it back and forth until the rewind spring anchor loop (8) engages. :Insert the screw (5) and tighten it down securely. :Go to Tensioning the Rewind Spring. Tensioning the Rewind Spring:Make a loop in the unwound starter rope and use it to turn the rope rotor six full revolutions counterclockwise. Hold the rotor steady – straighten the twisted rope – release the rotor – let go of rope slowly so that it winds onto the rotor. :Check spring tension: – The starter grip must be firmly seated in the rope guide bush. If the grip droops to one side: Add one more turn on rope rotor to increase spring tension. – When the starter rope is fully extended it must be possible to rotate the rotor another half turn. If this is not the case, the spring is overtensioned and could break. Take one turn of rope off the rotor. :Go to Fitting the Starter Cover. a 389BA029 KN a = 2mm (0.08 in) 8 392BA025 KN 392BA044 KN
35 HT 70, HT 75english Fitting the Starter Cover:Push the upper mounting boss under the shroud – line up the tank and push the lower part of cover onto the tank. :Insert and tighten down the housing screws. Secure cable lug (arrow) in position (if fitted on your machine).For periods of about 3 months or longer: :Drain and clean the fuel tank in a well ventilated area. :Run engine until carburetor is dry, this helps prevent the carburetor diaphragms sticking together. :Remove the saw chain and guide bar, clean them and spray with corrosion inhibiting oil. :Thoroughly clean the machine, pay special attention to the cylinder fins and air filter. :If you use a biological chain and bar lubricant, e.g. STIHL BioPlus, completely fill the chain oil tank. :Store the machine in a dry and high or locked location, out of the reach of children and other unauthorized persons. Replace the chain sprocket after using two chains! Replace sooner if the wear marks on the sprocket are deeper than about 0,02 (0.5 mm)(dimension a) since this would otherwise shorten the life of the chain. Use gauge – see Special Accessories – to check the depth of the wear marks. It is best to use two chains in rotation with one sprocket. Use only original STIHL chain sprockets! 410BA019 KN Storing the Machine Checking the Chain Sprocket a 390BA012 KN
36 english HT 70, HT 75HT 70:Remove the chain sprocket cover, chain and guide bar. :Use a screwdriver to remove the E- clip (1). :Pull the washer (2) and sprocket (3) off the gear shaft. :Clean the stub of the gear shaft and lubricate with STIHL grease – see Special Accessories. :Fit the new chain sprocket on the gear shaft. :Fit the washer and E-clip on the gear shaft. HT 75The chain sprocket is driven through a friction clutch. It may only be replaced by an authorized STIHL servicing dealer. Replacing Chain SprocketHT 70 1 23 386BA014 KN
37 HT 70, HT 75english Correctly sharpened chainA properly sharpened chain slices through wood effortlessly and requires very little feed pressure. Do not work with a dull or damaged saw chain as it will increase the physical effort required, produce unsatisfactory results and a higher rate of wear. :Clean the chain. :Check the chain for cracks in the links and damaged rivets. :Replace any damaged or worn parts of the chain and match the new parts to the shape and size of the original parts by filing back as necessary. It is necessary to comply with the angles and dimensions specified below. If the saw chain is incorrectly sharpened – especially if the depth gauges are too low – there is an increased risk of kickback and resulting injury!The pruner’s saw chain cannot be locked in place on the guide bar. Therefore, it is best to remove the chain from the bar and resharpen it on a workshop sharpening tool (FG 2, HOS, USG). :Select the appropriate sharpening tools for the chain pitch. See Specifications for the permitted chain pitches. The chain pitch (e.g. 3/8) is marked on the depth gauge of each cutter. Use only special saw chain files! Other files have the wrong shape and cut.Select the file diameter according to the chain pitch (se table Sharpening Tools at the end of this chapter). You must also observe the following angles when resharpening the chain cutters. A =Filing angle B =Side plate angle Cutter shape: Micro = Semi-chisel Specified angles A and B are more readily obtained if recommended files or sharpening tools and correct settings are used.Maintaining and Sharpening Saw Chain 3/8 689BA020 KN Chain type Angle (°) AB Picco Micro Mini (PMN) 30 85 A B 689BA021 KN
38 english HT 70, HT 75 Furthermore, the angles must be the same on all cutters. If angles are uneven the chain will run roughly, not in a straight line, wear quickly and break prematurely. As these requirements can be met only after sufficient and constant practice: :Use a file holder A file holder must be used for manual resharpening of saw chain (see table Sharpening Tools). The correct filing angles are marked on the file holder. For checking anglesUse a STlHL filing gauge (see table Sharpening Tools). This is a universal tool for checking the filing and side plate angles, depth gauge setting and cutter length. It also cleans the guide bar groove and oil inlet holes.File correctly:If you use an FG 2, HOS or USG sharpener: Remove the chain from the bar and sharpen according to instructions supplied with the tool. :Sharpen chain frequently; take away as little metal as possible – two or three strokes of the file are usually enough.:Hold the file horizontally (at right angle to side of guide bar) and file according to the angles marked on the file holder. Rest the file holder on the top plate and depth gauge. :Always file from the inside to the outside of the cutter. :The file only sharpens on the forward stroke – lift the file off the cutter on the backstroke. :Avoid touching the tie straps and drive links with the file. 689BA025 KN 90° 60° 85° 70° 80° 0° 35° 10° 30° 689BA022 KN 689BA018 KN 90° 689BA043 KN
39 HT 70, HT 75english :Rotate the file at regular intervals while filing to avoid one-sided wear. :Use a piece of hardwood to remove burrs from cutting edge. :Check angles with the filing gauge. All cutters must be the same length. If the cutters are not the same length, they will have different heights. This makes the chain run roughly and increases the risk of breakage of the chain. :Find the shortest cutter and then file all other cutters back to the same length – it is best to have this work done in a workshop on an electric grinder. Depth gauge settingThe depth gauge determines the height at which the cutter enters the wood and thus the thickness of the chip removed. Distance between depth gauge and cutting edge a = 0.018(0.45 mm). This setting may be increased by 0.008 (0.2mm) for cutting softwood in mild weather season – no frost.Lowering depth gaugesThe depth gauge setting is reduced when the chain is sharpened because the top plate of the cutter slopes downward towards the back. :Check the depth gauge setting every time you sharpen the chain.:Place a filing gauge (1) that matches the chain pitch on the chain – if the depth gauge projects from the filing gauge, the depth gauge has to be lowered. :File down the depth gauge until it is level with the filing gauge. 689BA023 KN a 689BA047 KN 1 689BA051 KN