Harley 45 Timer And Ignition
Article by Mark Trotta
Just like Ironhead and Shovelhead motors, Harley 45 flatheads do not have conventional distributors. What ignites the spark plugs is the ignition coil, which is activated by an ignition timer.
Mounted on right side of the engine on the gear cover, the ignition timer is also known as a circuit breaker.
Although they look similar to a distributor, there is no cap or rotor or wires, so it doesn't "distribute" anything.
It is simply a vertical shaft with a spiral gear on the bottom that runs off the rear intake cam. The top is a metal housing that contains a set of points and condenser.
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NOTE: Harley 45 timer installation will be covered in a future article.
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How A Harley 45 Ignition System Works
The ignition timer and coil work in tandem to fire the spark plugs. The timer's function is to signal the coil to fire, which sends spark to the plugs through the coil-attached plug wires.
Wasted Spark Ignition
In a wasted spark ignition system, both plugs fire simultaneously from the coil. As a spark plug ignites the fuel mixture on one cylinder's compression stroke, the other spark plug fires on the second cylinder's exhaust stroke.
Although wasted spark ignition sounds inefficient, it really isn't. The second spark needs only minimal power to jump across the plug's electrode, so not much power is lost one the other one. It also eliminates the need for a high-tension distributor, thus reducing parts needed and production costs.
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Magneto Ignition
High-performance flatheads, such as the WR factory racer, were equipped with a magneto ignition unit. Unlike an ignition timer, it doesn't require a coil or battery to produce spark. Instead, spark is created by internal magnets.
Although magnetos work well at higher speeds, they produce weaker spark at lower RPMs. This is why Mag-equipped bikes are harder to start.
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Mechanical vs Auto Advance
Two types of ignition timers were seen on Harley 45 flathead models. All two-wheeled models and Servi-Cars built before 1964 had mechanical advance timers. Servi models built from 1964 and up were fitted with auto advance timers.
With mechanical advance timers, cold starting was accomplished by moving (retarding) the timing unit in one of two ways; by using the handlebar mounted spark control grip or reaching down and twisting the unit by hand. Once the engine started and warmed up enough, the unit (or grip) was twisted back inward to it's fully advanced normal running position.
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Auto Advance Timer
In 1964, Servi-cars were upgraded to an auto advance ignition timer. They will retrofit all older models.
Underneath the points and condenser base plate is a pair of metal weights with springs. With the motor off or idling, the weights are at rest, and the timer is in the retard position. This helps cold engine starting.
Pictured: Auto Advance Timer with points and condenser base plate removed.
The spring-held advance weights don't move until the motor comes off idle, typically around 1500 RPM. Engine speed then forces the weights outward, which causes the timing to advance. When the weights come back to rest, the ignition timer goes back to the retard position.
Replace Mechanical Advance With Auto Advance Timer
Both styles of ignition timers are interchangeable with each other. Auto-advance doesn't make an engine run any better, it just makes it easier to operate. Custom bike builders like them because it's visually cleaner; removing the spark control grip and cable unclutters the handlebar area.
Shop: Auto Advance Timer
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Setting The Points
Recommended points gap for Harley 45 engines is .020 - .022". Note that there are two different size lobes on the ignition timer cam.
The narrower lobe works the front cylinder, and the wider lobe works the rear cylinder. They are easiest to set when on the wider cam.
Related Article: Harley Points And Condenser
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Spark Control Grip
This second hand grip, opposite the throttle, was known as the "spark control" grip. On a Servi-car, this could be either left-hand or right-hand side. It activated a cable which was attached to the timer assembly.
The spark control grip was also used to retard engine timing while under a heavy load, or during acceleration. This was done to avoid engine knock.
Many vintage riders simply do away with the cable-activated grip. As long as an external spring is holding the timer in the advance position, you can lean over and physically move the timer with your right hand.
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Spark Plugs
Recommended spark plugs for 45 flatheads with battery ignition is Harley-Davidson #3 or equivalent. Recommended spark plug gap is 025" to 030".
On my 1961 Servi-Car, I'm running Champion D16 plugs which are still readily available. These are the big plugs that take an 18mm wrench size. The stocking number for these plugs is Champion 516.
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Notes and Misc
Timer cams should be lightly lubricated (not over-lubricated) with a drop or two of grease.
Servi-Car auto timers (1964-1973) have a total of 30 degrees of advance.
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