How to Fix Old-School Ignition Points: DIY Auto Got a collector car with
ignition points? Here's how to replace the points and set the timing. By Mike
Allen December 18,2009 3:30 AM "It's not a heap,dad. It's a classic."That's
harder to justify when your classic muscle car won't start. Nothing like a
high-compression V8 combined with a battery that hasn't seen a charge for a
month and a half to make for slow cranking. Add in the indifferent,low-energy
spark and incorrect ignition timing caused by worn-out points,and you've got an
engine that won't fire--oh,and wet spark plugs too. Modern engines use
computer-controlled factory-preset self-adjusting ignition systems that never
change their timing,have no moving parts and never need maintenance. Yay! A
generation ago,every teenager,every mechanic and a lot of vehicle owners
understood the theory and practice of changing points and setting the timing.
Nonetheless,there are still plenty of older vehicles,outdoor power
equipment,boats and tractors that need periodic adjustment or replacement. The
distributor on these older vehicles performs two related tasks. The first uses a
simple on/off switch,the ignition points,to provide properly timed pulses of
12-volt electricity to the ignition coil. In the coil,essentially a transformer
Autel
MaxiTPMS TS401,it's stepped up to 10,000 to 20,000 volts. Then,the
high-voltage electricity from the coil returns to the distributor,where the
rotor inside parcels it out to the correct spark plug to ignite the fuel/air
mix. There's a lobed cam on the distributor shaft that pushes on a small rubbing
block on the movable side of the points. As the cam and distributor rotate,the
points open and close constantly. As they close,current from the ignition switch
flows through the contacts into the coil's primary windings and then off to
ground. This current generates a magnetic field in the coil's iron core. When
the points open a few degrees of crankshaft rotation later,the current is
interrupted,causing the magnetic field to collapse. This induces electrical
current into the secondary windings of the coil,where the current is raised to
20,000 volts or more. The high voltage now travels over to the distributor,where
the rotor metes the high-voltage pulses out to the correct spark plug. All that
current flowing across the points doesn't like to stop suddenly,and can initiate
a small arc,which eventually erodes the tungsten contacts. The condenser
cushions that arc,making point life much longer. But not infinitely long. As the
contacts and the plastic rubbing block,which contacts the point cam,wear,the
ignition points' clearance and timing constantly change. After thousands of
miles,the timing has shifted enough to affect performance,and the ritual of
changing the points and setting the timing becomes necessary. How often? Some
vehicles need to have the timing adjusted as often as every 10,000 miles to
maintain peak performance. High-revving engines will need premium points with a
high-pressure spring to keep the points from bouncing at increased revs. Some
points assemblies include the condenser,yet for others,it's a separate part.
Condensers are inexpensive enough that it makes no sense not to replace them
with every set of points. They should last as long as a set of points,20,000
miles at least. Kettering Ignition: Charles F."Boss"Kettering was one of the
founders of Delco,and the inventor of the battery-point-style ignition
system,first used by Cadillac in 1910. Wear,inaccuracy and high maintenance have
forced car manufacturers to abandon this system,replacing it with computers and
individual ignition coils for every cylinder--and no points to wear out. On
Point The function of the ignition system is to fire the spark plugs at the
correct time,just before the piston hits top dead center (TDC) on the
compression stroke,to ignite the fuel/air mixture,thence producing high pressure
in the cylinder to force the piston down and,subsequently,the wheels to move the
car forward. The spark plug normally fires anywhere from 10 to 45 degrees before
the piston reaches TDC,to allow the fuel/air mixture's flame front to traverse
the combustion chamber. It takes a few milliseconds for the pressure in the
cylinder to build,and waiting until TDC would make the pressure peak too late in
the piston's downward stroke to be most efficient. Under some engine-operating
conditions,the advance might adjust the ignition timing to as much as 45 degrees
before TDC. Signs of incorrect ignition timing include hard starting,spark
knock,poor power,overheating and decreased fuel economy autel. This Chevy V8 uses an old-school
Kettering-style ignition distributor. To set the timing after replacing the
points and condenser,you'll need,no surprise,an old-fashioned stroboscopic
timing light.
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