Husqvarna K770 Workshop Manual
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Husqvarna K770 Workshop Manual

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Workshop manual
K770
English
651 - 001 - 27.06.2018

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Summary of Contents for Husqvarna K770

  • Page 1 Workshop manual K770 English 651 - 001 - 27.06.2018...

  • Page 2: Table Of Contents

    Contents 1 Introduction 8 Wiring diagram 1.1 Document description..........3 8.1 Wiring diagram OilGuard........67 1.2 Target group............3 1.3 Revisions..............3 1.4 Safety..............3 1.5 Servicing tools............3 2 Safety 2.1 Safety definitions............4 2.2 General safety instructions........4 2.3 Symbols on the product......... 4 3 Servicing data 3.1 Symbols in the diagrams........5 3.2 Tightening torques..........

  • Page 3: Introduction

    1.5 Servicing tools The manual gives information about necessary servicing tools. Always use original tools from Husqvarna. 651 - 001 - 27.06.2018 Introduction - 3...

  • Page 4: Safety

    2 Safety 2.1 Safety definitions Always put on personal protective equipment: The definitions below give the level of severity for each signal word. • Hearing protection • Protective goggles or a visor • Breathing mask. WARNING: Injury to persons. This product in compliance with applicable EC directives.

  • Page 5: Servicing Data

    3 Servicing data 3.1 Symbols in the diagrams Tightening torque, Nm 651 - 001 - 27.06.2018 Servicing data - 5...

  • Page 6: Tightening Torques

    3.2 Tightening torques 6 - Servicing data 651 - 001 - 27.06.2018...
  • Page 7 11-12 17-23 10-12 11-13 11-13 11-13 651 - 001 - 27.06.2018 Servicing data - 7...
  • Page 8 25-30 9-11 1-1.5 38-42 8-10 4-10 8 - Servicing data 651 - 001 - 27.06.2018...
  • Page 9 20-25 25-30 9-11 10-12 651 - 001 - 27.06.2018 Servicing data - 9...

  • Page 10: Servicing Tools

    4 Servicing tools 4.1 Servicing tools overview Designation Used for Order No./ Source tion Air clearance gauge To adjust the air clearance between the ignition module and the fly- 502 51 34-02 wheel. Assembly punch To assemble the sealing rings of the crankshaft in the crankcase. 502 50 82-01 Bearing press To disassemble the primary bearing and assemble the crankshaft.

  • Page 11: Servicing Tools Overview

    4.2 Servicing tools overview Designation Used for Order No./Source tion Flywheel puller To disassemble the flywheel. 502 51 49-02 Grip plate To divide the crankcase. 544 06 00-02 Gudgeon pin punch To disassemble and assemble the gudgeon pin. 505 38 17-05 Hose catcher To catch the fuel filter in the tank.

  • Page 12: Servicing Tools Overview

    4.3 Servicing tools overview Designation Used for Order No./ Source tion Puller To disassemble the sealing rings of the crankcase in the crankcase. 504 91 40-01 Sealing plug To examine the crankcase for leaks. 503 55 22-01 Special screwdriver To adjust the idle speed. 501 60 02-03 Tachometer To adjust the idle and maximum speed.

  • Page 13: Product Overview For Repair And Servicing

    5 Product overview for repair and servicing 5.1 Components 1. Cutting blade 14. Throttle control 2. Blade guard 15. Rear handle 3. Handle for the blade guard 16. Throttle trigger lock 4. Front handle 17. Air purge bulb 5. Air filter cover 18.

  • Page 14: To Disassemble Into Basic Modules

    5.2 To disassemble into basic modules This chapter shows how you can disassemble and assemble the product in its basic modules. 14 - Product overview for repair and 651 - 001 - 27.06.2018 servicing...
  • Page 15 5.2.1 To remove the starter 3. Loosen the hoses by the water valve. Remove the belt from the pulley and remove the cutting head. 1. Loosen the 4 screws on the guard. 2. Remove the starter. 4. Remove the 2 screws on the rear belt guard. Remove the guard.
  • Page 16 5.2.3 To remove the air filter 5.2.4 To remove the cylinder cover 1. Remove the 3 screws and remove the cover. 1. Remove the 4 screws. 2. Push the collar of the rubber seal through the hole. 2. Remove the 2 screws and remove the filter holder and the filter.
  • Page 17 5.2.5 To remove the carburetor 4. Remove the hose to the air purge bulb. 1. Remove the screw. 5. Remove the throttle rod from the throttle control. 2. Lift the carburetor until you can access the gasoline hose and the hose to the air purge bulb. 5.2.6 To remove the air duct Remove the starter, air filter cover and cylinder cover before you remove the air duct.
  • Page 18 3. Remove the 3 screws on the air duct cover. Remove 5.2.7 To remove the muffler the air duct cover. Remove the cutting head the and the starter before you remove the muffler. 1. Loosen the four screws. 2. Remove the muffler. 5.2.8 Before you remove the vibration absorbers Before you remove the vibration absorbers you must remove the following parts.
  • Page 19 5.2.9 To remove the vibration absorbers 1. Remove the screws of the vibration dampers. 651 - 001 - 27.06.2018 Product overview for repair and servicing - 19...

  • Page 20: Repair And Servicing 6.1 Starter

    6 Repair and servicing 6.1 Starter 6.1.2 To attach the new starter rope 1. Put one end of the starter rope from the top through 6.1.1 To remove the starter rope the hole in the starter pulley. Then pull it out through the notch for the starter rope.
  • Page 21 6.1.4 To remove the starter pulley Note: Make sure that the spacer sleeve does not fall off. To remove the starter 1. Remove the spring force. See rope on page 20 . 1. Align the starter pulley notch with the end of the spring when assembling.
  • Page 22 6.1.8 To clean the spring assembly 6.1.11 To disassemble the starter pawls Note: Do not remove the spring from the assembly. Note: The position of the washer is below the starter pawls against the flywheel. Make a note of the position of the springs in relation to the flanges on the flywheel.

  • Page 23: Ignition System

    6.1.13 To install the starter The starter pawls must come into the correct position against the starter pulley sleeve. 1. Pull out the rope approximately 0.5 m. 2. Keep this position and set the starter against the product. 3. Slowly release the rope until the starter pawls come into the correct position.
  • Page 24 6.2.4 To examine the ignition spark .02 in. 1. Ground the spark plug against the cylinder. 0.5 mm 1. Replace the spark plug with the test spark plug. See Servicing tools overview on page 12 . 2. Move the stop button to the operation position. 3.
  • Page 25 6.2.6 To examine the ignition cable 6.2.7 To examine the short circuit cable and the stop switch 1. Pull up the rubber seal by the ignition unit and remove the ignition cable. 1. Remove the starter and the short circuit cable on the ignition unit.
  • Page 26 6.2.8 To remove the stop switch 4. Remove the switch. 1. Remove the screw and the cable. 6.2.9 To assemble the stop switch 2. Pull the right side of the switch halfway out. 1. Push the switch halfway into position. 2.

  • Page 27: Flywheel

    10–12 Nm. 6.3 Flywheel 6.3.1 To remove the flywheel A special tool from Husqvarna must be used to Servicing disassemble and assemble the flywheel. See tools overview on page 11 . The tool can be used on most flywheels on Husqvarna power cutters.

  • Page 28: Air Filter

    6. Put the screw press in the center and tighten it 6.3.3 To assemble the flywheel sufficient to make sure it is attached. The crankshaft and the center of the flywheel must be free from grease. Tightening torque 18–22 lbf·ft /25–30 Nm.

  • Page 29: Fuel System

    6.5.1 To remove the fuel filter To remove the fuel filter, use Husqvarna hose catcher. Servicing tools overview on page 11 . Refer to 1.
  • Page 30 6.5.3 To examine the fuel system for leakages 6.5.5 Function tank venting To examine the fuel hose, use a pressure monitor. Refer The tank has a check valve that let air enter the tank, Servicing tools overview on page 11 . Connect the but prevents fuel from running out.

  • Page 31: Carburetor

    2. This means that the fuel level in the carburetor does not get too high. 6.5.9 To examine the air purge To examine the air purge, use Husqvarna test Servicing instrument for fuel lines and check valves. See tools overview on page 11 Press the bladder of the pump.
  • Page 32 3. Remove the carburetor from the bracket. 6.6.2 To disassemble the guides 1. Remove the support insert. 4. Pull off the hose from the carburetor and divide the units. 2. Push out an edge of the guides, then push them out by hand.
  • Page 33 6.6.4 To assemble the inlet manifolds 1. Pull in the manifolds past their grooves on the plate. The parts must be installed correctly. Make a note that the guide to the inlet is irregular. 2. Push out the manifolds, one at a time, into their correct position.
  • Page 34 6.6.5 Carburettor components 1. Throttle valve as short as possible, this gives a more accurate test result. 2. Air valve 3. Choke valve 4. Pulse line, to the pump diaphragm of the carburetor 5. Fuel line 6. Connection to air purge 7.
  • Page 35 Make a note of the connection of the link rod. come from the venturi, can the function of the needle valve be examined as set out below. • Remove the 2 screws. 6.6.8.3 Water test 6.6.8 Needle valve To examine external leakage and the function of the needle valve, lower the carburetor into water.
  • Page 36 increase, the cause can be a damaged pump 3. Clean the seating. diaphragm. 6.6.9 To examine the pump diaphragm 1. Connect the pressure tester to the fuel pipe. 6.6.8.4 To examine and clean the needle valve Water test on page 35 . If the Do a pressure test, refer to 2.
  • Page 37 examine the measurement chamber diaphragm on page 1. Put a hose on the air purge bulb connection of the 38 . A hole in the diaphragm stops the fuel supply. carburetor 2. Blow in and out. The valve must close when you blow in to the carburetor and open when you blow out.
  • Page 38 6.6.13 To examine the measurement chamber opens. It also controls the quantity of fuel transmitted to the fuel side of the measurement chamber. diaphragm Assemble the parts in the order shown in the figure. The gaskets (1) are the same. 6.6.15 To examine the fuel strainer 1.
  • Page 39 3. Clean the channels with compressed air. The rings 6.6.18 High and low speed jets show where to blow clean. The low and high speed nozzles on the carburetor have been factory set. They must not be adjusted. 6.6.19 To adjust the idle speed The idle speed must be examined during service.

  • Page 40: Decompression Valve

    3. Adjust the idle screw to an idle speed of valve will close because of the combustion pressure, as approximately 2,700 rpm. in fig. 2. If the cutting blade rotates at this speed, the clutch or the friction retarder must be examined. 6.6.20 To assemble the air valve 1.

  • Page 41: Cylinder And Piston

    6.8 Cylinder and piston 6.7.3 To examine the decompression valve It is not necessary to start the product to examine the 6.8.1 To examine the compression of the cylinder decompression valve. The test shows leakage from the combustion chamber. 1. Make sure that the decompression valve moves. 1.
  • Page 42 CAUTION: Do not use the piston stop on this product. 1. Put the support plate below the piston. 1. Remove the cylinder. 2. Seal with a cloth or paper to make sure that parts do not fall into the crankcase. 2.
  • Page 43 4. Push out the wrist pin by hand. If it is tight, use a examined carefully. It is important to identify the cause small hammer and light force. of the unusual wear. 6.8.5 To examine cylinder wear Examine the cylinder bore against the light. You can 5.

  • Page 44: Piston Wear

    6.9 Piston wear 6.8.7 Piston wear tolerances The cause of engine failure can be hard to find if the 6.8.7.1 Piston ring play previous operation and service of the product is not If the piston ring play is more than .006 in/0.15 mm, the available.

  • Page 45: To Assemble The Piston

    6.10 To assemble the piston 6.9.3 Scoring Scoring occurs when the engine is too hot. The scores Lubricate new or cleaned bearings and piston rings with are usually on the exhaust side, which is the hottest. 2-stroke oil before you assemble them. The inlet side can show equivalent damage.

  • Page 46: To Assemble The Cylinder

    6.11 To assemble the cylinder 3. Install a circlip in the piston. Clean off remaining bits of the first gasket from the surfaces that connect with the gasket. 1. Put the gasket on the cylinder. 4. Hold the piston in position, push in the wrist pin and install the other circlip.

  • Page 47: Crankcase

    overview on page 11 . Before the test, turn the 4. Press down the cylinder on the piston and let the piston ring compressor move along the piston. crankshaft until the exhaust port is fully open. The piston Tighten the screws crosswise to a torque of 10–11 must be at its bottom turning point.
  • Page 48 Look for cracks on the crankcase. 6.12.2 To remove the crankcase seal To replace the crankcase seal rings, use a Husqvarna Servicing tools puller and an assembly punch. See overview on page 12 and Servicing tools overview on page 10 .
  • Page 49 Servicing tools overview on page 10 . To the puller. See 3. Put the grip plate over the hole for the crankshaft change the bearing you must use two Husqvarna and push out the crankshaft with the puller. 4. Push out the crankshaft from the other crankcase half in the same way.
  • Page 50 Servicing tools overview on page bearing press kits. See 3. Put the crankcase halves against a flat piece of 10 . wood or equivalent. Use a hot air gun around the bearing, max. 300 °F/150 °C. Put the sleeve from 1.
  • Page 51 3. Put the sleeve from the tool kit against the crankcase half. Tighten the mandrel on the Servicing tools Use a Husqvarna bearing press (refer to crankshaft by hand. overview on page 10 ) to assemble the bearings in the 2 crankcase halves.

  • Page 52: Clutch

    6.13 Clutch 6.13.1 To remove the clutch To remove the clutch you must use a Husqvarna piston stop. See Servicing tools overview on page 11 . Before you remove the clutch you must remove the cutting 52 - Repair and servicing...
  • Page 53 head, the rear belt guard, the air filter cover and the filter assembly. Do not replace one shoe from a different bracket. clutch as this causes bad balance. 1. Lock the crankshaft with the piston stop. The inner diameter of the clutch drum must not be more 2.
  • Page 54 6.13.4 To remove the clutch springs 6.13.7 Belt pulley bearings 1. Put a large screwdriver in each spring end. The clutch drum and belt pulley are connected units. The belt pulley has two permanently lubricated ball 2. Expand the spring using circlip pliers and remove bearings that are adjacent to each other without the spring.

  • Page 55: Cutting Head

    3. Pull out the bearing by tightening the nut. Note: When you install the clutch, you must first put the washer on the crankshaft. 6.14 Cutting head 6.14.1 To disassemble the blade guard/bearing housing 1. Remove the cutting head from the product. 6.13.9 To install the belt pulley bearings 1.
  • Page 56 3. Put the cutting head in a vise with the pulley pointing 6. Loosen the screws. Remove the seals and screen down. rings. 4. Lock the belt pulley with a mandrel or a screwdriver. Note: The illustration shows the screwdriver and the wrench from below.
  • Page 57 speed, the brake shoes are pushed out from the brake 6.14.5 To assemble the retarder unit drum. The retarder does not operate. 1. Put the spring (1) in position in the guide plate (2). Note where the spring ends must be. 6.14.3 To disassemble the friction retarder 1.
  • Page 58 1. Assemble the plate of the retarder unit and the belt If you replace the blade shaft bearings with a hydraulic pulley with the 4 screws. press, use the Husqvarna bearing press made to Servicing tools overview disassemble the bearing. See on page 10 .
  • Page 59 6.14.8 To assemble the blade shaft bearings If you replace the blade shaft bearings with a hydraulic a) Put the bearing press made for bearing press, use the Husqvarna bearing press made to assembly as in the illustration. Servicing tools overview disassemble the bearing.

  • Page 60: Wet System

    6.15 Wet system 4. With a plastic hammer, push or hit the axle down until the spacer touches the inner ring of the bearing. 6.15.1 Function 5. Use the assembly support (2) to make the bearing Each side of the blade guard has a spray nozzle. The housing level.

  • Page 61: Throttle Trigger And Throttle Lock

    3. Open the hose clip with a screwdriver. 3. Close the hose clip with a pair of pliers. The hose clip can be used again. 6.16 Throttle trigger and throttle lock 6.15.3 To assemble the wet system 1. Put the spray nozzles on to the blade guard. 6.16.1 To remove the throttle trigger and throttle lock Note: When you remove the throttle lock, use a v-jaw...

  • Page 62: Oilguard

    6.16.2 To examine the throttle lock incorrect fuel. For the OilGuard to operate, an oil The throttle lock operates correctly if the throttle is containing dye, “Husqvarna OilGuard oil”, must be locked at idle speed. added. Fuel analysis starts 10 seconds after startup and 1.
  • Page 63 oil, the light goes through the fuel. The light hits the 6.17.2 To examine the power supply for the phototransistor and an electronic switch (4) engages OilGuard and sets the engine speed limit to 3800 rpm. 1. Remove the filter and cylinder cover. 2.

  • Page 64: Troubleshooting

    7 Troubleshooting 7.1 Engine does not start Remove the spark plug from the cylinder. Hold the cylinder, pull the starter rope and see if there are sparks between the spark plug electrodes. There are no sparks at the spark plug Examine Cause Solution...

  • Page 65: Engine Stops During Operation - No Sparks

    7.2 Engine stops during operation - no sparks There are no sparks at the spark plug Symptom/Category Cause Solution Engine suddenly The switch is accidentally set to off Set the switch to the left position stops The plug cap is not attached Attach the plug cap fully The switch cable or high-voltage cable is Replace...

  • Page 66: Weak Output Or Change Of Speed

    7.4 Weak output or change of speed There are no sparks at the spark plug Symptom/Category Cause Solution Compression is good Air has gone through the fuel pipe joint. Make sure it is tight and there is no flame Air has gone into the fuel pipe because of a Replace crack or pin hole Air has gone through the pulse pipe...
  • Page 67 8 Wiring diagram 8.1 Wiring diagram OilGuard 1. OilGuard - OilGuard plug - ignition module 2. OilGuard - stop switch - ignition module 3. OilGuard - stop switch - ground 651 - 001 - 27.06.2018 Wiring diagram - 67...
  • Page 68 596432401 2018-06-27...

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