Model A & B

Ford Garage

Timing is Everything

but What is It?

Proper timing is very important for optimized and reliable operation!

The result of improper timing is never favorable!

Hell, you might even shoot your own propellor off!
(or blow holes in the tops of your pistons!)

Model A Ford enthusiasts love to talk about timing!
If the hood is open or someone has a car running not quite right, then you can bet someone nearby is talking about timing.

The thing I have often noticed is that many people are not quite clear about what 'timing' is, and are sometimes confused by different aspects of 'timing' as it relates to engine operation.

There are two distinct and different types of 'timing' which affect an engine's operation and performance.

The first is Valve or Camshaft timing

The second is Ignition or Spark timing.

Valve or Camshaft Timing:

Valve or camshaft timing is the mechanical relationship between the movement of the crankshaft and pistons, and the movement of the camshaft and intake and exhaust valves.

Valve or camshaft timing controls when, and for how long, the air fuel mixture from the carburetor is drawn into the cylinder for compression, as well as when, and for how long, the exhaust is released from the cylinder.

The valve timing is mechanically designed into the engine to control the valve opening and closing events, as well as the rates of valve movement and lift relative to both crankshaft angular position, and piston travel and position.

The valve movements are controlled by the design of the engine camshaft lobe profiles, as shown above.

While the engine is running, the valve timing is a fixed mechanical relationship, and is neither speed dependent nor adjustable on a Model A or B engine.

The valve timing is controlled by the mesh of the camshaft and crankshaft gears, the profile of the lobes on the camshaft, and by the clearances between the valve stems and tappets.

Ignition or Spark Timing:

Ignition or Spark timing is the relationship of the firing of the spark plug relative to the piston (and crankshaft and camshaft) position.

The distributor (or ignition system) controls the electrical saturation of the ignition coil and the collapse of the electrical field strength, and thus controls the resulting spark energy intensity from the secondary winding of the coil.

That spark energy from the coil is delivered by the distributor to the appropriate individual spark plug, and is delivered in the proper sequence for the four-cylinder four-cycle engine.

The actual spark timing is controlled by the start and stop of current through the ignition coil by the action of the primary contact points in the distributor. The opening of the contact points breaks the current through the coil's primary windings, and releases the energy to the spark plug through the rotor and distributor body and cap.

The mechanical contact points in the distributor are operated (and timed) by the rotation of the distributor cam inside the distributor body. Both the cam and points are located under the rotor. The distributor shaft (and the oil pump shaft) are gear-driven off of the engine (valve) camshaft, which in turn is gear-driven off of the engine crankshaft.

The ignition timing sequence and profile is determined by the shape and rotational position of the distributor cam relative to the crankshaft position, as well as the size of the contact point gap compared to the design specified gap.

Changes in contact point gap affect both the coil saturation (dwell time) as well as the actual spark timing (instant of firing).

Wear between the movable contact point arm rubbing block and the distributor cam surface causes a reduction in point gap over time, and effectively retards the spark timing (as well as increasing the dwell time). This is not desirable.

The contact point gap is statically adjustable in both the Model A and Model B distributors by loosening the clamp screw on the point block and screwing the stationary contact point in or out to change the gap.

In the Model A ignition distributor, the relative rotational position between the distributor contact points and distributor cam can be varied manually while the engine is running (by the adjustment of the spark advance lever on the steering column).

In the Model B ignition distributor, the relative rotational position between the distributor contact points and distributor cam varies automatically with change in engine rpm based on the response of a centrifugal flyweight advance mechanism (shown above) built inside the Model B distributor.

Also, the static spark timing position of the Model B distributor can be manually externally adjusted plus/minus several crankshaft degrees by loosening a screw and rotating the upper contact point plate as shown above.

Each hash mark is equal to 2 crankshaft degrees. Move the plate clockwise to advance the timing, and counter-clockwise to retard the timing.

So how do you know if your engine is timed right?

Watch this short entertaining video from Tex Willis to be sure!

More related information on Ford Garage:

  1. For more Model A & B related information, use the Site Search box at the top or bottom of this page.
  2. Model A, B, & Model 46 Camshaft Gear Timing Cover Differences
  3. Model A & B Camshaft to Crankshaft Gear Alignment
  4. Model A & B Camshaft to Crankshaft Positioning
  5. Model B Distributor Advance Operation
  6. Model A & B Valve Tappet Adjustment ~ Rule of Nine
  7. Model A & B KR Wilson BV-45 Step Feeler Gauge
  8. Model A & B Camshaft Specifications
  9. Model A & B Bill Stipe's Camshaft Specifications
  10. Model B & Model 46 Distributor Design Details
  11. Model B & Model 46 Pertronix Ignitor Distributor Timing Procedures
  12. Model A Remund Pertronix Electronic Ignition Instructions
  13. Model A & B Ignition Components Interchange Table
  14. Model A Condenser Capacitance
  15. Model A & B Condenser Details
  16. Model A Distributor Lower Plate Wiring Solution
  17. Model A Nu-Rex Centrifugal Spark Advance Unit
  18. Model A Phillips Automatic Spark Control Unit
  19. Model A & B & V8 Vacuum Gauge Tuning from ARSCO
  20. Model A & B & V8 World War II Training Film: Automotive Troubleshooting. 1942 on YouTube
  21. Model A & B & V8 World War II Training Film #497: Mechanics, Champion Ignition and Spark Plug. c. 1941-1945 on YouTube

June 2006