12-12-2012, 06:38 PM
The Model T Ford Ignition System and Spark Timing
[attachment=43652]
The authors have been discussing this subject for some
time, each approaching the project with differing objectives.
Steve was interested in optimizing ignition timing for racing
purposes and Ron wanted to write an article that would
clearly explain the original Model T ignition system. Our
peer reviewers challenged us. It was a convergence of
interests and we all had great fun learning the truth about
what we believed we already understood.
Before we discuss the details of spark timing, lets
review the unique features of the various components of the
original Model T ignition system.
Figure 1 is an original Ford timer case and roller. This
is important because there were many different manufacturers
of timers other than Ford and they vary significantly in
mechanical design and construction. The Ford timer case
can be usually identified by the word “Ford” in script
stamped into the main case near where the pull lever is
affixed and the roller has similar markings on the spring
loaded roller support arm, see Figure 2. The timer case has
four electrical conductive metal segments mounted in a nonmetallic
insulator at equally spaced intervals around the
inside circumference of the case. Each conductive segment
has an insulated screw that extends outside the case
perimeter forming a screw terminal with thumbnut where
wiring to the coil box can be connected. The timer roller is
mounted on the end of the camshaft, indexed with a pin and
retained by a locking nut. The roller rides on the inner
surface of the timer case connecting engine ground to each
conductive segment as it rotates thereby completing the
electrical circuit to each coil.
Summary
As you can see in Figure 7, when running on battery,
linear spark timing can be obtained by moving the spark
lever. This would appear best for optimum engine
performance, but Model T coils do not work well on the 6
volt battery at higher engine speeds.
As you can see in Figure 8, when running on the
magneto, timing advance is not linear. The spark lever is a
selector that, when moved, determines the magneto current
pulse where the ignition coil will supply spark voltage to the
plug.
The authors would like to formally thank Bruce
McCalley, Trent Boggess and John Regan for their review of
drafts of this article. Without their detailed knowledge,
critical eye and encouragement, this article could not have
been completed.
[attachment=43652]
The authors have been discussing this subject for some
time, each approaching the project with differing objectives.
Steve was interested in optimizing ignition timing for racing
purposes and Ron wanted to write an article that would
clearly explain the original Model T ignition system. Our
peer reviewers challenged us. It was a convergence of
interests and we all had great fun learning the truth about
what we believed we already understood.
Before we discuss the details of spark timing, lets
review the unique features of the various components of the
original Model T ignition system.
Figure 1 is an original Ford timer case and roller. This
is important because there were many different manufacturers
of timers other than Ford and they vary significantly in
mechanical design and construction. The Ford timer case
can be usually identified by the word “Ford” in script
stamped into the main case near where the pull lever is
affixed and the roller has similar markings on the spring
loaded roller support arm, see Figure 2. The timer case has
four electrical conductive metal segments mounted in a nonmetallic
insulator at equally spaced intervals around the
inside circumference of the case. Each conductive segment
has an insulated screw that extends outside the case
perimeter forming a screw terminal with thumbnut where
wiring to the coil box can be connected. The timer roller is
mounted on the end of the camshaft, indexed with a pin and
retained by a locking nut. The roller rides on the inner
surface of the timer case connecting engine ground to each
conductive segment as it rotates thereby completing the
electrical circuit to each coil.
Summary
As you can see in Figure 7, when running on battery,
linear spark timing can be obtained by moving the spark
lever. This would appear best for optimum engine
performance, but Model T coils do not work well on the 6
volt battery at higher engine speeds.
As you can see in Figure 8, when running on the
magneto, timing advance is not linear. The spark lever is a
selector that, when moved, determines the magneto current
pulse where the ignition coil will supply spark voltage to the
plug.
The authors would like to formally thank Bruce
McCalley, Trent Boggess and John Regan for their review of
drafts of this article. Without their detailed knowledge,
critical eye and encouragement, this article could not have
been completed.