The STIHL HS 72 and HS 74 are hedge trimmers designed for cutting hedges and shrubs. These are high-speed cutting tools, and their operation requires adherence to specific safety precautions to minimize the risk of personal injury. The manual emphasizes that careless or improper use can lead to serious or even fatal injury.
Function Description:
The hedge trimmer is a single-cylinder, two-stroke engine-powered tool. Its primary function is to trim hedges and shrubs using steel cutter blades. The HS 74 model features a rear handle with a twist lock, allowing it to be rotated 90° to the left or right for improved control and comfort during operation. The engine's speed is controlled by a throttle trigger, which must be depressed after activating the throttle trigger interlock. A starting lock helps prevent cutter blade movement during startup. For cold starts, a fuel pump bulb provides additional fuel feed.
Important Technical Specifications:
- Engine: Single cylinder, two-stroke.
- Displacement: 23.9 cm³ (1.46 cu.in).
- Bore: 33 mm (1.20 in).
- Stroke: 28 mm (1.10 in).
- Power: 0.8 kW.
- Max. permissible engine speed: 10,500 rpm (adjustable via carburetor).
- Idle speed: 2800 r.p.m.
- Ignition System: Electronic (breakerless) magneto ignition.
- Spark Plug (suppressed): Bosch WSR 6 F or NGK BPMR 7 A; Heat range 200.
- Electrode gap: 0.5 mm (0.02 in).
- Spark plug thread: M 14 x 1.25; 9.5 mm (0.37 in) long.
- Carburetor: All-position diaphragm carburetor with integral fuel pump.
- Air filter: Foam and felt elements.
- Fuel tank capacity: 0.37 L (0.78 US pt).
- Fuel mixture: Gasoline and oil mixture (STIHL 50:1 or other branded TC oils 25:1).
- Weight (complete unit):
- HS 72/420: 5.1 kg (11.2 lb)
- HS 72/550: 5.3 kg (11.7 lb)
- HS 74/420: 5.2 kg (11.5 lb)
- HS 74/550: 5.4 kg (11.9 lb)
- HS 74/700: 5.6 kg (12.3 lb)
- Cutter blade length (HS 72/74): 550 mm (21.7 in).
- Sound pressure level Lpeq (according to ISO 6081): 95 dB (A).
- Sound power level Lweg (according to ISO 3744): 102 dB (A).
- Vibration measurement (idle speed, m/s²):
- HS 72: Right handle 3.0, Left handle 3.7
- HS 74: Right handle 2.0, Left handle 2.1
- Vibration measurement (max. engine speed, m/s²):
- HS 72: Right handle 10.7, Left handle 4.1
- HS 74: Right handle 6.8, Left handle 6.7
Usage Features:
- Starting: The hedge trimmer is a one-person machine. It should be started and operated outdoors in a well-ventilated area, under good visibility and daylight conditions. The starting procedure involves moving the starting lock lever, squeezing the throttle trigger, moving the slide control to the starting throttle position, setting the choke lever (for cold or warm start), pressing the fuel pump bulb, and then pulling the starter grip. Once the engine fires, the throttle trigger should be blipped to move the slide control to the "Run" position.
- Handling: Always hold the hedge trimmer firmly with both hands, with the right hand gripping the rear handle. The rear handle of the HS 74 can be rotated for better control. Never operate the hedge trimmer with one hand.
- Working Conditions: Operators should be in good physical and mental health, not fatigued, and not under the influence of substances. Proper protective clothing, including goggles or safety glasses, ear protection, heavy-duty gloves, sturdy clothing, long pants, and non-slip boots, is mandatory. A safety hard hat is recommended where there is a danger of head injuries.
- Fueling: Use a mixture of brand-name unleaded gasoline (minimum 90 ROZ/89 pump octane) and quality two-stroke engine oil with TC classification (STIHL 50:1 or other branded 25:1). Fueling should be done outdoors in well-ventilated areas, away from open flames. The fuel filler cap should be removed carefully to release pressure slowly, and tightened securely after fueling.
- Cutting Technique: When working close to the ground, ensure no sand, grit, or stones get between the cutter blades. If blades jam, switch off the engine immediately before attempting to free them. Avoid working on ladders, in trees, or on any insecure support. Do not use the hedge trimmer above shoulder height or with one hand. The cutter blades tend to run on for a short period after the throttle trigger is released (flywheel effect).
- Break-in Period: For new machines, avoid running at high revs (full throttle off load) for the first three tank fillings to allow moving parts to bed in and reduce frictional resistances. Maximum power is achieved after 5 to 15 tank fillings.
- Operation: After extended full-throttle operation, allow the engine to idle for a while to dissipate heat and protect engine-mounted components.
Maintenance Features:
- General Checks: Regularly inspect the hedge trimmer for proper condition and operation, including the throttle trigger, interlock, stop switch, cutting tool, and starting lock. Check for loose parts, cracks, bends, or damage to blades. Keep blades sharp.
- Cutter Blades: Always spray cutter blades with STIHL resin solvent before and after work to protect them and reduce friction. Clean away filing or grinding dust and lubricate blades with grease after sharpening.
- Air Filter: Clean the air filter if there's a noticeable loss of engine power. This involves removing the foam and felt elements, washing them in non-flammable cleaning solution (e.g., warm soapy water), drying them, and replacing any damaged elements.
- Carburetor Adjustment: The carburetor is factory-adjusted for optimum performance. Readjustment (using a tachometer) may be necessary for operation at high altitude or sea level, or if the engine runs poorly. Adjusting screws (H for high speed, L for low speed, LA for idle speed) control engine speed and mixture.
- Spark Plug: Check the spark plug if the engine is low on power, difficult to start, or runs poorly. Clean dirty spark plugs, check the electrode gap (0.05 mm / 0.02"), and replace after approximately 100 operating hours or if electrodes are badly eroded.
- Spark Arresting Screen: Check and clean the spark arresting screen in the muffler if the engine is low on power. Replace if damaged or coked up.
- Muffler: Do not operate if the muffler is damaged, missing, or modified. Keep the engine and muffler free from cuttings, chips, leaves, fibers, and excess lubricant to reduce fire risk.
- Gearbox Lubrication: Lubricate the spur gears with STIHL multipurpose grease (0781 120 1109/10) every 25 hours of operation.
- Starter Rope and Rewind Spring: Instructions are provided for replacing the starter rope and rewind spring, including steps for tensioning the rewind spring.
- Fuel Tank: Drain and clean the fuel tank periodically. For long-term storage, drain the fuel tank and run the engine until the carburetor is dry to prevent diaphragms from sticking.
- Storage: Store the machine in a dry, safe place, out of reach of children.
- Parts: Use only STIHL replacement parts for maintenance and repair. Warranty claims are accepted only if repairs are performed by an authorized STIHL Service Shop using original STIHL spare parts.
The manual also includes a warning regarding engine exhaust containing chemicals known to the State of California to cause cancer, birth defects, or other reproductive harm.
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