IH: Engine Control - Sub-01B

Magneto Ignition System

(58-59 XLC and 58-69 XLCH) 1) 2)
The magneto produces a high voltage discharge to the spark plug which is timed to each cylinder's compression stroke.
It also eliminated the need for a battery for ignition. 3) as you can kick start or bump start the bike at about 2-1/2 MPH or less. 4)

  • Components include a single induction coil, a rotating magnet (rotor), a condenser, a circuit breaker and a circuit breaker cam. 5)
  • Ignition is timed when the front cylinder piston is 11/16“ / (45° of crankshaft rotation) before TDC on the compression stroke.
    Upon setting the proper timing adjustments at the factory;
    Timing alignment marks were stamped on the drive housing plate and rear edges of the magneto adapter plate for future timing adjustments. 6)
  • A grounding circuit is connected to a button on the right handlebar (stop switch) that breaks the circuit to the ignition and stops the engine.
  • Magneto mount changes:
    • (1958-1964) Magneto is mounted in a fixed position producing advanced spark timing only.
    • (1965-1969) Magneto is mounted on a movable plate allowing for spark timing retard.

Keyed Mags

The key mounted to the magneto locks or unlocks the ground to the system. 7)
When locked, the spark is sent to ground and the bike shuts off. 8)
When unlocked, the spark is sent to the mag (removes the ground) and the bike will operate.

Lights were operated by a toggle on the visor, no other key needed.
Or, no key needed as long as the mag is in the unlocked position.

Keys on mags have been known to break, i.e. stuck or worse sending there little metal bits into the mag. 9)
However, some run fine with the key.
Keys can be made / replaced (using the number on the lock) in the case of a broken one. 10)

Solid Mount Magneto

Fairbanks-Morse Magneto (keyed) 11)
Fairbanks-Morse Magneto 12) Magneto on a 72 XLCH 13)
Magneto on a 77 XLCH 14)

Adjustable Mount Magneto

AKA Retard Mag (Timing is mechanically advanced)
It's almost like a VOES switch for your mag! 15)
The Morris Auto Advance, uses a small spring under the mag base. 16)
The MM3 uses a bronze ring and a steel base. 17)
The MM2 uses a steel ring and a bronze base.
Tighten up the nuts to create a slight drag, retard the spark for starting and the vibration + the spring will advance the unit.

Morris Magneto (MM3) 18)
Keyed magneto on a 69 XLCH 19)

Timing Advance Spring

The spring used is not a heavy one.
You can use a spring similar the old carb return springs on autos. 20)

Or a simple coil hook spring: 21)
Hooked it to the bolt on the tappet block and the spring hooked to the indent for the coil bolts.
Unhook, retard, start, hook it back up.

Makeshift Advance Spring 22)

Timing Advance Cable

You can also attach a choke cable to the primary to control the advance. 23)

Or, a twist lock cable setup:

Do a search for push-pull controls and look for a locking one.
The L-bracket on the case can be fabricated to mount the T-handle cable lock.
The arm on the magneto, at the cable connect, is possibly available through a vintage parts supplier or used.
The cable is held by a pivot and a set screw. 24)

1952-1959 HD Spare Parts Catalog for all Sportster and K Models pg 19
1960-1970 HD Sportster Parts Catalog pg 18
5) , 6)
1959-1964 HD Sportster 55 OHV FSM pg 5F-13
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