Ignition Timing (Total Timing Method)

 

Ignition Timing (Total Timing Method)

 

 

This issue's subject is about setting ignition timing using the total timing method.  This is intended for application with pre-emmission engines (generally pre-1975).  This article will be especially helpful on non-stock engines or engines with a non-stock distributor.  As you can recall from the last issue, ignition timing consists of three variables;  initial advance, mechanical advance and vacuum advance.  What is commonly referred to as total timing consists of an initial advance plus mechanical advance.  When setting initial and/or mechanical advance, the vacuum line should be temporarily disconnected and plugged (carb side).  Most factory specs call for an initial plus mechanical advance figure totaling in the area 30-36 crankshaft degrees.  Most Chevy V8's perform best with total timing set between 36-40 degrees (depending on engine, drivetrain and vehicle).  This does not include vacuum advance and is assuming manifold vacuum controlled advance of pre-emmission engines.  Later emission control engines had port above the throttle plate) vacuum controlled advance, which requires lower total timing figures.  To set total timing you must first mark the 36 degree, or total advance desired, location on the harmonic balancer.  To do this, measure the circumference of the balancer with a flexible, cloth or paper tape, measurer or install permanent degree tape to the balancer.  You can also measure the diameter of the balancer and multiply by "pi" (3.14). 

Make a mark 36 degrees clockwise from the existing "0" mark on the balancer.  To find the distance, you must use your high school algebra skills, to find the inches equivalent of 36 degrees.  Example helps here;  if you have a seven inch balancer; 7x3.14=21.98 or 22 inches in circumference. Therefore, X/22=36/360.  Where x=792/360=2.2.  So X=2.2 inches or 2 3/16 inches.  Make your formula then measure the distance clockwise from "0" and make your new mark.  Put on safety glasses for the next procedure.  Also well deserving of  caution is revving the engine while under the hood and in line of belts or fans, if they become dislodged or break serious injury could occur.  Connect a timing light and rev the engine until the new mark stops advancing, that's when the centrifugal advance is completely advanced or "all in". 

Compare the mark to the "o" mark on the fixed timing tab on the engine, then loosen the distributor clamp and turn the distributor until the new 36 degree mark on the balancer lines up with the fixed "0" mark on the tab.  Later you can adjust slightly to what best suits your specific engine setup.  With the engine at idle, note the new advance setting if different from specs.  Reconnect the vacuum advance systems.  If pinging is encountered while driving, you can slightly retard the timing advance, increase the octane of gas or recurve the mech and vacuum advance systems.  If you had to rev the engine past 3500 rpm to get the mark to stop advancing, the mechanical advance in the distributor should be recurved in order establish best performance and ensure fuel economy.