Starting Circuit; Testing Procedure Starting Circuit - Tecumseh V-twin Technician's Handbook

STARTING CIRCUIT

After all of the safety interlock switches have been
activated, the starter switch closes the starting circuit.
The electrical current running through the armature
windings of the electric starter motor produces a strong
magnetic force. The armature magnetism repels the
magnetism produced by the permanent field magnets of
the electric starter. The repelling magnetic forces cause
the armature to rotate, moving the drive pinion laterally
on the splined armature shaft. The rotating starter pinion
gear then meshes with the flywheel ring gear. When the
drive pinion contacts the stop at the end of the armature
shaft, the pinion rotates along with the armature shaft to
rotate the engine. The armature and pinion remain
positively engaged until the engine fires and the flywheel
rotates faster than the armature. The greater momentum
of the flywheel throws the starter pinion gear out of mesh
and forces the starter pinion back to the disengaged
position. After the switch is released, the starting circuit
is opened and the armature coasts to a stop. A small
anti-drift spring holds the pinion in the disengaged
position.
TESTING PROCEDURE STARTING
CIRCUIT
CAUTION: FOLLOW
PRECAUTIONS WHEN TESTING FOR A.C.
VOLTAGE, ELECTRIC SHOCK CAN KILL.
1. Check the battery using an electrical load 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.
NOTE: Load testers drawing no more than 50-60
amperes should be used.
2. Check the electric starter terminal for the required
voltage (12 v D.C.) using a voltmeter. (Illust. 5-10)
5-8
3. Check wiring, connections, circuit breakers, fuses,
4. Isolate the engine from the equipment it is powering.
5. If the engine binds only on the compression stroke,
ALL SAFETY
If the engine turns over freely, the electric starter should
be replaced or disassembled and repaired if allowed
under various country regulations. See "Service" in this
chapter. If the preceding steps fail to correct the problem,
the engine will require to be disassembled to find the
mechanical failure. See Chapter 7 under "Disassembly
Procedure".
If the engine does not turn over, a mechanical binding
may be the cause. Check for proper lubrication, (oil level
and viscosity) check the electric starter gear and flywheel
ring gear interference. If no problem is discovered, the
problem is an internal failure.
5-10
ignition or starter switch, safety switches, and
solenoid for continuity using an ohmmeter or
continuity light. Repair or replace as necessary.
Remove all equipment loads (belts, chains, and
couplers). TEMPORARILY BY-PASS THE SAFETY
INTERLOCK DEVISES.
NOTE: ALL safety switches must be in proper
working condition. Repair or replace as needed.
check the valve clearance per the specification table
in Chapter 10. If the valve clearance is within the
specifications, the compression release may require
service. To diagnose the camshaft compression
release, remove both valve covers and bring the
engines number one cylinder up to TDC on the
compression stroke. The exhaust valve should briefly
open just before TDC. Repeat this procedure on the
number two cylinder. If either of the exhaust valves
do not open disassembly and removal of the
camshaft will be required. See Chapter 7. Valve
clearance not within the listed specifications will
require adjustment of the rocker arms to obtain the
proper clearance.