4-CYCLE OVERHEAD VALVE ENGINES - Small Engine Discount

TESTING PROCEDURE
STARTING CIRCUIT
1. Check the power source using an electrical tester and following the tester's recommended procedure.
Make sure the battery meets the minimum battery voltage requirements found in the original equipment
manufacturer's service manual.
2. Check the electric starter terminal for the required voltage (12v D.C. or 120v A.C.) using a voltmeter.
CAUTION: FOLLOW ALL SAFETY PRECAUTIONS WHEN TESTING FOR A.C. VOLTAGE, ELECTRIC
SHOCK CAN KILL.
3. Check wiring, connections, fuses, ignition or starter switch, safety switches, or solenoid for continuity
using a ohmmeter or a continuity light. Repair or replace as necessary.
4. Remove all equipment loads from the engine. Take off all drive belts, chains, and couplers to isolate
the engine from the equipment it is powering.
5. Try to turn the engine over using the recoil assembly if equipped. If the engine doesn’t turn over, a
mechanical binding may be the cause. Check for proper lubrication (oil level and viscosity) and check
for electric starter gear and flywheel ring gear interference. If no problem is discovered, the problem is
an internal failure.
6. If the engine binds only on the compression stroke, check the engine valve clearance per the
specification table in Chapter 10. If the valve clearance is within the specifications, the camshaft
(compression release failure) may require replacement. Valve clearance not within the listed
specifications will require resetting the rocker arms to obtain the proper clearance.
7. If the engine turns over freely, the electric starter should be replaced or disassembled and checked.
See "Service" in this chapter. 120 volt starters labeled UL Listed/CSA Approved can be serviced;
however, starters labeled CSA must only be replaced. If the preceding steps fail to correct the problem,
the engine will require to be disassembled to find the mechanical failure. See Chapter 9 under
"Disassembly Procedure".
CHARGING CIRCUIT
The following pages will show wiring diagrams of several Tecumseh charging systems. The charging system
used on the engine is best identified by obtaining the engine model number and the specification number on
the engine. Consult a Tecumseh dealer or a parts manual to identify the charging system. To make many of the
tests it is necessary to run the engine and measure alternator output with a voltmeter. When making voltage
tests with the engine running, it is not necessary to take readings at all the listed R.P.M.s. Checking at one of
the speeds is sufficient.
In some cases an open circuit D.C. check cannot be
made. A SCR (Silicon Controlled Rectifier) is located
in the circuit which requires a minimum “turn on”
voltage to allow it to conduct. Without the battery in
the circuit this “turn on” voltage is not present. The
SCR “senses” this and there will be no D.C. output
from the regulator / rectifier.
Each charging system has its own testing procedure.
Test the charging system using the applicable
procedure found on the following pages.
350 Milliamp Charging System
CHECKING THE SYSTEM: The battery must be in
the circuit to perform the test properly. Set the
voltmeter to the 0 - 20 D.C. volt scale. Connect a
voltmeter across the battery. The voltmeter should
read the battery voltage. Start the engine. With the
engine running, there should be an increase in the
voltage reading. If there is no change in the voltage
reading, the alternator is defective and should be
replaced. See Chapter 9 for "Disassembly Procedure"
(diag. 7).
40
MAGNETO GROUND
(GR)
(-) ENGINE GROUND
BATTERY GROUND (BL)
RED
BLACK
D.C. OUTPUT
LEAD (RED)
Not For Resale
www.SmallEngineDiscount.com
(+) POSITIVE LEAD
ELECTRIC STARTER
LEAD (ORG)
7