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For Parts Call 606-678-9623 or 606-561-4983
Professional Shop Manual
78/83/90 Series Horizontal Shaft Engines
(277/357/420 cc Engines)
NOTE: These materials are for use by trained technicians who are experienced in the service and repair of outdoor power
equipment of the kind described in this publication, and are not intended for use by untrained or inexperienced individuals.
These materials are intended to provide supplemental information to assist the trained technician. Untrained or ine
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For Parts Call 606-678-9623 or 606-561-4983 Table of Contents Chapter 1: Introduction Professional Service Manual Intent. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Fasteners. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Assembly instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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For Parts Call 606-678-9623 or 606-561-4983 Chapter 4: The Fuel System and Governor Inspecting the fuel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Test fuel for alcohol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Fuel tank vent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 The fuel filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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For Parts Call 606-678-9623 or 606-561-4983 Chapter 7: Ignition System Troubleshooting the ignition system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 Stop switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 Remote (ignition) stop switch (snow engines) . . . . . . . . . . . . . . . . . . . . . . . 83 Test for ignition that won’t turn off . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 The module
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For Parts Call 606-678-9623 or 606-561-4983 Introduction CHAPTER 1: INTRODUCTION Professional Service Manual Intent This manual is intended to provide service dealers with an introduction to proven diagnostic and repair proce- dures for 78/83/90 series MTD horizontal shaft engines. Disclaimer: The information contained in this manual is correct at the time of writing. Both the product and the infor- mation about the product are subject to change without notice. About the text format: NOTE: Is
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For Parts Call 606-678-9623 or 606-561-4983 78/83/90 Series Horizontal Shaft Engines • Be prepared in case of emergency: ! ! CA CAU UT TIO ION N Keep a fire extinguisher nearby Keep a first aid kit nearby Keep emergency contact numbers handy • Replace any missing or damaged safety labels on shop equipment. • Replace any missing or damaged safety labels on equipment being serviced. • Grooming and attire: Do not wear loose fitting clothing th
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For Parts Call 606-678-9623 or 606-561-4983 Introduction Fasteners • Most of the fasteners used on the MTD engine are metric. Some are fractional inches. For this reason, wrench sizes are frequently identified in the text, and measurements are given in U.S. and metric scales. • If a fastener has a locking feature that has worn, replace the fastener or apply a small amount of releas- able thread locking compound such as Loctite® 242 (blue). • Some fasteners, like cotter pins, are single-use ite
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For Parts Call 606-678-9623 or 606-561-4983 78/83/90 Series Horizontal Shaft Engines Model and serial number The model and serial number can be found on a white sticker with a bar code. The sticker is located on the right side of the engine at the bottom of the block. See Figure 1.1. Front of engine NOTE: The serial number will always start with the model number. Model /serial number Figure 1.1 MTD Horizontal Engine Model Designators 1 6 1 - S H A Starter/Alternators
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For Parts Call 606-678-9623 or 606-561-4983 Introduction Maintenance The information in this manual applies to the MTD engine. Some basic principles may apply to engines pro- duced by other manufacturers. As the saying goes “an ounce of prevention is worth a pound of cure”. The same can be said about preventive maintenance on outdoor power equipment. By changing the spark plug and oil at recommended intervals many fail- ures can be avoided. NOTE: Please refer to Chapter 7: Igniti
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For Parts Call 606-678-9623 or 606-561-4983 78/83/90 Series Horizontal Shaft Engines Air filter (summer engines) Generally air filters come in two different types, a Paper-pleated element pleated-paper element or foam. A combination of the two are used on the MTD engine. See Figure 1.3. 1. The main function of the air filter is to trap air borne particles before they enter the engine. Dirt ingestion can cause serious internal engine damage. NOTE: Snow engines do not have air filters becaus
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For Parts Call 606-678-9623 or 606-561-4983 Introduction Oil type and capacity MTD engines use oil with a SF/SG API rating or better is the recommended oil for this engine. The winter engines use SAE 5W-30 oil and the summer engines use SAE 10W-30 oil. The oil capacity for all of the 78/83/90 series engines is 37 fl.oz (1.1 liters). • Check the oil level frequently and change the oil more frequently in severe operating conditions such as exceptionally deep snow falls. • Synthetic oil is a su
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For Parts Call 606-678-9623 or 606-561-4983 78/83/90 Series Horizontal Shaft Engines To check the oil with a threaded dip stick: Do not thread 1. Twist and remove the dip stick from the engine. dipstick in to check the oil level 2. Clean the oil off of the tip of the dipstick. 3. Re-insert the dipstick without threading it in to get the oil level reading. See Figure 1.5. 4. The oil level is determined by the lowest point on the dipstick that is completely covered with oil. Figure 1.5 Fully s
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For Parts Call 606-678-9623 or 606-561-4983 Introduction Fuel Gasolines currently on the market are not pure gasoline. Today’s fuels have alcohol and other additives in them to reduce emissions. The fuel make up can vary seasonally and geographically. Fuel with alcohol added to it is sometimes referred to as “oxygenated fuel”. The extra oxygen carried by the etha- nol increases the oxidation of the fuel. This speeds up the process that causes the fuel to go bad. Excessive alcoh
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For Parts Call 606-678-9623 or 606-561-4983 78/83/90 Series Horizontal Shaft Engines To replace the fuel filter: Front fuel tank shroud To avoid personal injury or property ! ! W W A AR RN NIIN NG G damage, use extreme care in han- dling gasoline. Gasoline is extremely flammable and the vapors are explosive. Serious personal injury can occur when gasoline is spilled on yourself and/or your clothes which can ignite. Wash your skin and change clothes immediately. Remove these screws 1. Sip
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For Parts Call 606-678-9623 or 606-561-4983 Introduction Valve lash Valve lash is the clearance between the top of the valve stem and the rocker arm. The valve lash should be checked after the first 25 hours of use and every 100 hours after that. Valve lash can be checked and adjusted using the following steps: Spark plug socket 1. If the engine has been run, allow it to cool thoroughly. Position the equipment for easy access to the cylin- der head. 2. Disconnect the high-tension le
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For Parts Call 606-678-9623 or 606-561-4983 78/83/90 Series Horizontal Shaft Engines Probe to confirm piston 6. Slowly pull the starter rope until air can be heard is at top of travel coming out of the spark plug hole. 7. Confirm that the piston is at Top-Dead-Center on Valves closed the compression stroke. See Figure 1.13. (push rods slack) • The compression stroke can be distinguished from the overlap stroke by the presence of air Push rods pressure at the spark plug hole and the fact that
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For Parts Call 606-678-9623 or 606-561-4983 Introduction 13. Double-check the clearance after tightening the jam nut, to confirm that it did not shift. Re-adjust if necessary. 14. Rotate the engine through several compression cycles: • Observe the movement of the valve gear. • Return the piston to TDC compression stroke and re-check the valve lash to confirm consistent movement of the valve gear, including the slight bump to the exhaust valve from the automatic compression release. 15. Clean-
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For Parts Call 606-678-9623 or 606-561-4983 78/83/90 Series Horizontal Shaft Engines General torque specifications
