MTD P90 Series Professional Shop Manual
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MTD P90 Series Professional Shop Manual

Vertical shaft engines
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For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983
For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983
Professional Shop Manual
P90 Series Vertical Shaft 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 inexperi-
enced individuals should seek the assistance of an experienced and trained professional. Read, understand, and follow all
instructions and use common sense when working on power equipment. This includes the contents of the product's Oper-
ators Manual, supplied with the equipment. No liability can be accepted for any inaccuracies or omission in this publication,
although care has been taken to make it as complete and accurate as possible at the time of publication. However, due to
the variety of outdoor power equipment and continuing product changes that occur over time, updates will be made to these
instructions from time to time. Therefore, it may be necessary to obtain the latest materials before servicing or repairing a
product. The company reserves the right to make changes at any time to this publication without prior notice and without
incurring an obligation to make such changes to previously published versions. Instructions, photographs and illustrations
used in this publication are for reference use only and may not depict actual model and component parts.
© Copyright 2011 MTD Products Inc. All Rights Reserved
www.mymowerparts.com
www.mymowerparts.com

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Summary of Contents for MTD P90 Series

  • Page 1 Instructions, photographs and illustrations used in this publication are for reference use only and may not depict actual model and component parts. © Copyright 2011 MTD Products Inc. All Rights Reserved www.mymowerparts.com...
  • Page 2 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 www.mymowerparts.com www.mymowerparts.com...

  • Page 3: Table Of Contents

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Table of Contents Chapter 1: Introduction Professional Service Manual Intent ........1 Safety .
  • Page 4 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Chapter 4: The Fuel System and Governor Inspecting the fuel ..........33 Test fuel for alcohol .
  • Page 5 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Chapter 8: Exhaust Spark arrestor (if equipped) ........79 Muffler removal/replacement .
  • Page 6 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 www.mymowerparts.com www.mymowerparts.com...

  • Page 7: Professional Service Manual Intent

    • Common sense in operation and safety is assumed. • In no event shall MTD be liable for poor text interpretation or poor execution of the procedures described in the text. • If the person using this manual is uncomfortable with any procedures they encounter, they should seek the help of a qualified technician or MTD Technical Support.
  • Page 8 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines • Be prepared in case of emergency: ! CAUTION ! CAUTION Keep a fire extinguisher nearby Keep a first aid kit nearby Keep emergency contact numbers handy •...

  • Page 9: Fasteners

    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®...
  • Page 10 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines MTD Vertical Engine Model Designators 1 P 6 1 M U A • Starter/Alternator 1=Recoil start Major Revision •...

  • Page 11: Model And Serial Number

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Introduction Model and serial number The model and serial number can be found on a white sticker with a bar code. The sticker is located between the dipstick and the muffler.

  • Page 12: Spark Plugs

    Cleaning the spark plug: NOTE: MTD does not recommend cleaning spark plugs. Use of a wire brush may leave metal deposits on the insulator that causes the spark plug to short out and fail to spark. Use of abrasive blast for cleaning may cause damage to ceramic insulator or leave blast media in the recesses of the spark plug.

  • Page 13: Air Filter

    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. Air filters used on the MTD engine are designed to prevent particles larger than 3-5 micron from passing through into the engine.

  • Page 14: Oil Type And Capacity

    P90 Series Vertical Shaft Engines Oil type and capacity The recommended oil for MTD engines is an SAE 10W-30 oil with an SM API rating or better. The oil capacity for all of the P90 series engines is 57 fl.oz (1.7 liters).

  • Page 15: Changing The Oil

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Introduction Changing the oil The oil change interval is every 100 hrs. NOTE: The first oil change should be preformed at 8 hours.

  • Page 16: Oil Filter

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Oil filter To replace the oil filter: Drain the oil by following the steps described in the previous section of this chapter.

  • Page 17: Fuel System

    Carefully slide the fuel lines off of the filter. If there are pieces of rubber on the barbs of the fuel filter, replace the affected fuel line. IMPORTANT: The P90 series engines uses low permeation fuel line to meet EPA guidelines. When replacing the fuel lines, they must be replaced with the same type of low permeation fuel line.

  • Page 18: Valve Lash

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines 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.
  • Page 19 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Introduction .005” feeler gauge Check valve lash between each valve stem and rocker arm using a feeler gauge. Intake valve lash (top valve) should be 0.004” - 0.006”...

  • Page 20: Exhaust System

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Exhaust system The exhaust system is a frequently overlooked component of an engine. It is important to make sure the muffler is in good condition and free of blockage.

  • Page 21: Definitions

    Also check attachments for damage and make sure they are firmly mounted. Steps to troubleshooting NOTE: The steps and the order of the steps that follow are a suggested approach to troubleshooting the MTD engine. The technician does not necessarily have to follow them as described in this chapter.
  • Page 22 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines IV. Unusual exhaust tone There are tools that the technician can use in order to define the problem, such as: Interview the customer.

  • Page 23: Identify Factors That Could Cause The Problem

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 ASIC ROUBLESHOOTING Identify factors that could cause the problem This is the second step in the troubleshooting process. Crankshaft will not turn. A.
  • Page 24 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Run the engine with a spark tester in-line between the spark plug wire and the spark plug or use an oscilloscope and see if the spark goes away at the same time the engine dies.
  • Page 25 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 ASIC ROUBLESHOOTING V. Makes unusual smoke when running a. Black smoke, usually heavy, usually indicates a rich air fuel mixture • Not enough air: air flow blockage or a partially closed choke. •...
  • Page 26 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines chirping noise. • Confirm with a compression test and leak-down test. e. Unusual exhaust tone Splashy or blatty •...

  • Page 27: Repairing The Problem

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 ASIC ROUBLESHOOTING Repairing the problem The third step in the troubleshooting process is to repair the problem. This step consists of: A. Form a diagnosis by using all of the information gathered from the troubleshooting that was performed. B.

  • Page 28: Prime Test

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Prime test To perform a prime test: Prime the engine through the carburetor throat using a squirt bottle, filled with clean fresh gasoline.
  • Page 29 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 ASIC ROUBLESHOOTING Compare the results to the following chart. Leak-down Testing Results Symptom Possible cause Air escaping from Worn cylinder or piston rings. the breather Possible blown head gasket Air escaping from...

  • Page 30: Compression Test

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Compression test To perform a compression test: NOTE: Compression should be in the range of 55 - 80 PSI (3.8 - 5.5 Bar).

  • Page 31: Pcv Testing

    The cause of this oil burning can be mistaken for a worn-out engine, if proper diagnosis (compression, leak- down, and case pressure) is not performed. Experimentation by MTD’s Training and Education Department has revealed the following characteristics of MTD engines: •...
  • Page 32 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines www.mymowerparts.com www.mymowerparts.com...

  • Page 33: Air Filter

    A combination of the two are used on the MTD engine. See Figure 3.1. • Air filters used on the MTD engine are designed to prevent particles larger than 3-5 micron from pass- ing through into the engine.
  • Page 34 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Lift the air filter cover off the engine. Remove the air filter assembly. Air filter Figure 3.3 Install the air filter by following the previous steps in reverse order.

  • Page 35: Blower/Air Filter Housing

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 NTAKE YSTEM Blower/air filter housing On the P90 series of engine, the air filter housing is part of the blower housing. To remove/replace the blower/air filter housing: Remove the air filter following the steps described in the previous section of this chapter.

  • Page 36: Carburetor And Insulator

    Disconnect the fuel line from the carburetor. NOTE: MTD uses low permeation fuel lines to meet EPA guidelines. Low permeation fuel lines are made with a soft membrane that lines the inside of the line. Any tear in this membrane will allow the fuel to get in between the membrane and the hose, choking off the fuel flow.
  • Page 37 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 NTAKE YSTEM Double nut the carburetor studs and remove them. See Figure 3.10. NOTE: The insulator block and gaskets may fall out when the studs are removed.
  • Page 38 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Install the carburetor by following the previous steps in reverse order. Gasket Gasket NOTE: Use new gaskets between the cylinder...

  • Page 39: Chapter 4: The Fuel System And Governor

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 YSTEM AND OVERNOR CHAPTER 4: THE FUEL SYSTEM AND GOVERNOR The function of the fuel system is to store fuel, mix the fuel with air in the correct ratio and deliver it to the intake port.

  • Page 40: Test Fuel For Alcohol

    This results in less power for the engine. A 10% ethanol (E10) mix is acceptable for MTD engines. Anything higher than that will result in performance issues.

  • Page 41: Choke/Throttle Cable Adjustment

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 YSTEM AND OVERNOR Choke/throttle cable adjustment The choke/throttle cable will need to be adjusted any time the cable or the control panel is replaced. NOTE: The procedures to remove/replace the choke/throt- Choke lever tle cable can be found in the service manual for the...

  • Page 42: Carburetors

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Carburetors If diagnosis indicates a fuel problem, inspect the carburetor. This is important even if problems are identified elsewhere in the fuel system.

  • Page 43: Disassembly And Rebuilding The Carburetor

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 YSTEM AND OVERNOR Disassembly and rebuilding the carburetor Remove the carburetor by following the procedures described in Chapter 3: Air Intake System. NOTE: An insulator separates the carburetor from the cylinder head.
  • Page 44 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines NOTE: Because the float valve is crucial to the func- Float tioning of the carburetor and the viton tip of...
  • Page 45 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 YSTEM AND OVERNOR Throttle stop screw The throttle stop screw has a large pliable lip around the head of the screw. That lip secures a metering Welch plug plug for the pilot and transition ports.
  • Page 46 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Transition ports Pilot port NOTE: The pilot screw regulates how much of this pre-mixed fuel/air emulsion is allowed to...

  • Page 47: Engine Speed Adjustment

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 YSTEM AND OVERNOR Engine speed adjustment To adjust the engine speed: Start the engine and let it reach operating tempera- ture. Move the throttle control lever to the full throttle posi- tion.

  • Page 48: Afterfire Solenoid

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Afterfire solenoid When an engine is turned off, the engine does not “instantly” stop spinning. As the engine slows down, it is still drawing fuel out of the carburetor.
  • Page 49 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 YSTEM AND OVERNOR Old style NOTE: Early production engines have a simple bullet con- nector between the stator and the afterfire solenoid (power lead).

  • Page 50: Testing The Afterfire Solenoid

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Testing the afterfire solenoid An afterfire solenoid that is not working properly can prevent the engine from starting. The solenoid itself rarely fails, usually there is some type of fault in the wiring to the solenoid to prevent it from energizing.
  • Page 51 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 YSTEM AND OVERNOR With the ignition key in the “on” position, test for volt- Afterfire solenoid lead from main harness age at the power lead connection. See Figure 4.21. •...

  • Page 52: Governor

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Governor The engine speed is controlled by a balance between the force applied by a spring (pulling the throttle open) and a flyweight mechanism within the engine apply- ing force to the governor arm (pushing the throttle closed).
  • Page 53 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 YSTEM AND OVERNOR Put an alignment mark on the governor arm and shaft. See Figure 4.26. Loosen the nut and T-bolt that secures the governor arm to the shaft.

  • Page 54: Governor Shaft

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Governor shaft To remove or replace the governor shaft: Remove the engine from the equipment that it pow- ers.

  • Page 55: Chapter 5: Lubrication

    CHAPTER 5: LUBRICATION Oil type and quantity The recommended oil for MTD engines is an SAE 10W-30 oil with an SM API rating or better. The oil capacity for all of the P90 series engines is 57 fl.oz (1.7 liters).

  • Page 56: Oil Dipstick

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Oil dipstick To check the oil: Fully seat the dip stick Twist and remove the dipstick from the engine.

  • Page 57: Lubrication System

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Lubrication Lubrication system The 4P90 engine uses a combination pressurized and splash lubrication system. There is an oil pump in the Balance shaft sump that is driven by the balance shaft.
  • Page 58 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Check the oil level. NOTE: Top off the oil as needed with an SAE 10W- 30 oil with an SM API rating or better Start the engine.

  • Page 59: Positive Crankcase Ventilation Valve

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Lubrication Positive crankcase ventilation valve The PCV valve is located under the flywheel and allows the crankcase pressure to escape. The function and test procedures for the PCV is covered in Chapter 2: Basic Troubleshooting.
  • Page 60 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Inspect the oil drain-back port. Make sure it will allow oil to drain back into the engine.

  • Page 61: Chapter 6: Starter And Charging Systems

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Starter and Charging System CHAPTER 6: STARTER AND CHARGING SYSTEMS Starter removal To remove/replace the starter assembly: Starter screws Disconnect the negative battery cable. Disconnect the starter cable using a 10 mm wrench.

  • Page 62: Bench Testing The Electric Starter

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Bench testing the electric starter IMPORTANT: Always bench test an electric starter before condemning it. To bench test an electric starter: Remove the starter by following the procedures described in the previous section of this chapter.

  • Page 63: Rebuilding The Starter

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Starter and Charging System Rebuilding the starter The starter motor used on the 4P90 engine is a perma- nent magnet dc motor with a radial commutator, similar to what is found in a repulser start motor.
  • Page 64 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Slide the stator housing off of the starter. Pull the rotor out of the stator housing. NOTE: The rotor will be held to the stator by strong Rotor magnets.
  • Page 65 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Starter and Charging System 12. Remove the nut and washers from the cable stud using a 10 mm wrench. See Figure 6.10. Washers 13.
  • Page 66 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Remove the screw, indicated by the arrow in Figure 6.13., from the topside of the starter gear housing using a #2 phillips screwdriver.
  • Page 67 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Starter and Charging System Screw extractor 22. Remove the bushing from the clutch/pinion cover. See Figure 6.16. NOTE: A blind hole bearing puller with a 11mm arbor or an screw extractor can be used.
  • Page 68 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines To re-assembly a starter motor: Press the bushing into starter gear housing until there is 0.055” (1.4 mm) sticking out.
  • Page 69 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Starter and Charging System Clutch/pinion gear assembly Insert the clutch/pinion gear assembly into the starter gear housing. See Figure 6.21. Figure 6.21 Install the pinion gear.
  • Page 70 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Clean the carbon from the commutator. NOTE: A pencil eraser is very effective in cleaning commutators. See Figure 6.24.
  • Page 71 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Starter and Charging System 11. Press a new bushing into the end cap until it is flush with the casting. See Figure 6.27. Bushing is flush with casting Figure 6.27 positive brushes/cable stud assembly...
  • Page 72 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines NOTE: A special tool will be needed to compress the brushes for assembly of the motor. See Figure 6.30.
  • Page 73 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Starter and Charging System 22. Set the starter motor onto the end cap while keeping the brushes compressed into the brush holder. See Figure 6.33.

  • Page 74: Charging System

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Charging system The charging system used on MTD engines consists of a dual output alternator and a rectifier/regulator. The charging system has a 5 amp AC output and a 3.75 amp DC output.

  • Page 75: Charging System Testing

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Starter and Charging System Charging system testing To test the charging system: Locate the connection between the engine harness Engine harness and the main harness of the machine. connector See Figure 6.37.
  • Page 76 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines If the results do not match the specifications: 11a. Turn off the engine. 11b. Disconnect the regulator/rectifier.

  • Page 77: Stator

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Starter and Charging System Stator To remove/replace the stator: Remove and ground the spark plug wire. Remove the flywheel by following the steps described in Chapter 7: Ignition System.

  • Page 78: Rotor

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Rotor Rotor failures are extremely rare. To check the rotor: • Confirm that the magnets are firmly attached to the flywheel.

  • Page 79: Chapter 7: Ignition System

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Ignition System CHAPTER 7: IGNITION SYSTEM Troubleshooting the ignition system The purpose of the ignition system is to provide a spark in the combustion chamber at the proper time to efficiently ignite the fuel/air mixture.

  • Page 80: The Module

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines The module The coil in this ignition system is an inductive discharge magneto, contained in a single module.

  • Page 81: Module Removal

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Ignition System Module removal Unplug the spark plug. Remove the blower/air filter housing by following the Afterfire solenoid lead steps procedures in Chapter 3: Air Intake System. Disconnect the module wire that goes to the system harness.

  • Page 82: Installing The Module And Setting The Air Gap

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Installing the module and setting the air gap Plastic feeler gauge NOTE: If just setting the air gap, loosen the module mounting screws first then follow the proce- dures described below.

  • Page 83: Flywheel

    A sheared flywheel key will throw off the ignition timing. Sheared keys are uncommon on MTD engines. If one is found, check the crankshaft and flywheel for damage.

  • Page 84: Spark Plug

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Spark plug • The spark plug is a F6RTC, part #951-10292, gapped to 0.024” - 0.031” (0.6 - 0.8 mm).

  • Page 85: Spark Arrestor (If Equipped)

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Exhaust CHAPTER 8: EXHAUST The exhaust system is a frequently overlooked component of an engine. It is important to make sure the muffler is in good condition and free of debris and/or insects.

  • Page 86: Muffler Removal/Replacement

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Muffler removal/replacement Remove the four screws, indicated by the arrows in Figure 8.2. that retain the muffler shield using a 10mm wrench and lift it off of the engine.
  • Page 87 Clean all of the gasket material off of the cylinder head and the muffler. See Figure 8.6. NOTE: The MTD engine uses a graphite exhaust gasket. It is not reusable and must be replaced every time the muffler nuts are loosened.

  • Page 88: Catalytic Converter

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Catalytic converter On engines equipped with a catalytic converter muf- fler, there is an air injector assembly on the cylinder head, as show in Figure 8.7.

  • Page 89: Cylinder Head Removal

    Cylinder head CHAPTER 9: CYLINDER HEAD Cylinder head removal The Cylinder head of the MTD engine can be removed without removing the engine from the piece of equipment. To remove the cylinder head: Disconnect and ground the spark plug high tension lead.
  • Page 90 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Remove the two screws, indicated by the arrows in Figure 9.3, that secure the baffle to the cylinder using an 8 mm wrench.
  • Page 91 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Cylinder head Sealing surface 14. Lift the cylinder head off of the engine. 15. Carefully clean all sealing surfaces of all gasket resi- due.

  • Page 92: Cylinder Head Installation

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Cylinder head installation Place a new head gasket on the cylinder, allowing the alignment dowels to hold it in place.

  • Page 93: Valves

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Cylinder head Valves The valves and valve seats can be serviced by grinding and lapping or the head can be replaced. Depending on local machine and labor costs, it is probably more economical to replace the cylinder head versus servicing the valves.
  • Page 94 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Lift the springs off of the valve stems. Slide the valves out of the cylinder head. NOTE: Only the intake valve has a valve guide seal.
  • Page 95 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Cylinder head Test the valves for leaks by: 11a. Place the cylinder head on a couple of wood blocks with the valves facing up. 11b.

  • Page 96: Push Rod Guide Plate

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Push rod guide plate The push rods move through a guide plate that aligns the push rods with the rocker arms. The guide plate also acts as a bushing for the push rods.
  • Page 97 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Crankshaft, piston and connecting rod CHAPTER 10: CRANKSHAFT, PISTON AND CONNECTING ROD The exact procedure a technician uses to disassemble an engine depends on the type of repairs needed. This chapter is written as a set of procedures that should provide the user with sufficient information to complete any fea- sible repair to the engine short block assembly.
  • Page 98 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Align the timing marks on the cam and the crank- shaft to allow easier removal of the cam and to help protect the compression relief from damage.
  • Page 99 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Crankshaft, piston and connecting rod 15. Match mark the connecting rod and cap. 16. Remove the connecting rod cap using a 10mm wrench.

  • Page 100: Crankshaft Inspection

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Crankshaft inspection Inspect the crankshaft journals and the crank pin for galling, scoring, pitting or any other form of damage.

  • Page 101: Piston Inspection

    Figure 10.9 Top piston ring Install rings back onto the piston. NOTE: The compression rings on the MTD engine have Middle piston different profiles. It is important that the proper pro- ring filed ring is on the right groove. See Figure 10.10.
  • Page 102 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Measure the gap between the ring and the ring land using a feeler gauge and compare the measure- ment to the chart at the end of this chapter.

  • Page 103: Connecting Rod Inspection

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Crankshaft, piston and connecting rod Connecting rod inspection Inspect the connecting rod for cracks or any signs of Measure at damage. right angles Measure at Install the rod cap and tighten to a torque of 177 - 212 right angles...

  • Page 104: Balance Shaft

    (the counter-weight piston, piston pin and one-third of the connecting rod). The crankshafts on MTD engines are not balanced. Extra Reciprocating weight is added to the crankshaft counter-weight to reduce mass the total reciprocating and rotational forces.

  • Page 105: Reassembly

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Crankshaft, piston and connecting rod Reassembly Clean the cylinder 1a. Remove all gasket material from all mating surfaces. 1b. Clean the cylinder and crank case cover. Oil seals 2a.
  • Page 106 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Install the balance shaft by: Timing marks Pre-lube the balance shaft with clean 10W-30 motor oil Rotate the crankshaft until the timing mark on the larger gear points to the 7:30 position.

  • Page 107: Engine Specifications Chart

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Crankshaft, piston and connecting rod Engine specifications chart Specification Minimum Maximum Service Limit Bore 3.544” 90.01 3.544” 90.02 3.553” 90.25 Cylindricity 0.000” 0.000 0.000”...
  • Page 108 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Specification Minimum Maximum Service Limit Compression ring end gap 0.008” 0.20 0.016” 0.40 0.039” 1.00 Scraper (second) ring end gap 0.008”...

  • Page 109: Engine Torque Values Chart

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Crankshaft, piston and connecting rod Engine torque values chart Fastener in lbs Blower housing studs 80 - 106 9 - 12 Breather cover 53 - 71 6 - 8 Carburetor drain bolt...
  • Page 110 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines www.mymowerparts.com www.mymowerparts.com...

  • Page 111: Abrasive Ingestion

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Failure Analysis CHAPTER 11: FAILURE ANALYSIS A properly maintained engine will provide years of service. Occasionally an engine will fail. An important part of working on engines is being able to recognize the root cause of engine failures.
  • Page 112 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines When particles enter the combustion chamber, the Cross hatch polished off up and down motion of the piston grinds the parti- cles into the side of the cylinder walls and damages the cylinder wall, piston and piston rings.
  • Page 113 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Failure Analysis Because the oil suspends the particles, the engine components that are immersed in oil will show defi- nite signs of abrasive ingestion especially around the connecting rod and main bearing journals.

  • Page 114: Insufficient Lubrication

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Insufficient lubrication The bearing surfaces in an engine are not smooth. The machining processes used to make the engine parts, leave little peaks and valleys that are only visible under a microscope.
  • Page 115 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 Failure Analysis Discoloration Metal transfer is the primary indicator that the film of oil between two engine parts has been violated. If the damage is localized, a general failure of the lubri- cation system is probably not the cause.

  • Page 116: Engine Overspeed

    P90 Series Vertical Shaft Engines Engine Overspeed The MTD engine is designed for a maximum speed of 3300 rpm. When the governor is unable to control the engine rpm, the engine can accelerate past the safe maximum speed. When an engine runs beyond its designed speed, a few things happen: As the piston moves up and down in the cylinder, it builds momentum.

  • Page 117: Overheated

    Overheated The MTD engines are air cooled engines. Because of this, cleanliness of the engine is very important to the life of the engine. Dirt, grass and sludge all form an insulating layer on the engine. This will trap the heat in the engine and cause it to over heat.

  • Page 118: Mechanical Breakage/ Wear

    For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 P90 Series Vertical Shaft Engines Mechanical Breakage/ Wear Sometimes an engine fails because a part breaks. There are generally three causes of a broken part, outside of the previously discussed engine failures.
  • Page 119 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 www.mymowerparts.com www.mymowerparts.com...
  • Page 120 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 For Discount Cub Cadet Parts Call 606-678-9623 or 606-561-4983 MTD Products Inc - Product Training and Education Department FORM NUMBER - 769-06294 10/2011 www.mymowerparts.com www.mymowerparts.com...

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