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Install Your Chevy Distributor
(Point-Style Distributors. HEI systems
can be installed using similar techniques, but photos in this article do
A distributor can actually be dropped into a block
in virtually any orientation and made to function by re-arranging the
spark plug wires to match the installation. You will see this approach to
distributor installation quite frequently, and it is a sure-fire tip-off
that the engine builder/distributor installer didn’t have a clue
about how to do the job right.
GM always installed the distributor in a
specific orientation, and always used the same distributor cap
“tower” for the #1 spark plug. By following this procedure,
your distributor will be installed in the correct factory position for a
1. Bring the engine up to Top Dead
Center on the Compression Stroke and align the timing mark on the harmonic
balancer with the 8-degree mark on the timing chain cover (or wherever you
want the engine to fire. 8 Degrees is a good starting point for an initial
start-up, but you can set it anywhere from 6 to 12 degrees before top
To Find Top Dead Center on the Compression Stroke
with the engine in the car:
a. Remove the #1 spark
b. Disconnect the coil wire from the
distributor cap and ground it
c. Have a helper plug
the #1 spark plug hole with a finger.
d. With the
starter, slowly “bump” the engine over until the helper feels
air being forced by his finger.
You are now coming up on the
compression stroke. Align the timing marks as noted above.
Find Top Dead Center on the Compression Stroke with the engine out of the
a. Remove the valve cover on the
driver’s side of the engine to expose the valves for cylinder
b. Rotate the crankshaft until the timing mark
approaches top dead center. Observe the exhaust valve.
If the exhaust valve is moving as you are approaching top dead center, you
are on the exhaust stroke.
You need to rotate the crankshaft one more
d. If neither valve is moving as you approach
top dead center, you are on the compression stroke.
Align the timing
marks as noted above.
2. Install the rotor to the
3. Hold the distributor body in the orientation show
in figure 1 relative to the engine/block and drop the distributor straight
down into the block. Pay no attention to rotor orientation at this time.
If the rotor is aligned with the oil pump driveshaft, the distributor will
drop all the way down and seat. If the rotor does NOT line up, the
distributor will not drop all the way down.
4. If the distributor
does NOT drop all the way down (chances are best that it won’t),
pull the distributor up out of the block just enough to disengage the
rotor from the camshaft gear, and turn the rotor a little bit. Drop it
down again. Repeat this until the distributor drops all the way down and
the rotor engages with the oil pump.
5. The distributor will now
be all the way into the block, but the rotor will not be properly aligned.
You can now pull the distributor up until the cam gear disengages, turn
the rotor JUST A HAIR (half a cam tooth), and drop it straight back down
again. The rotor will now move one tooth over, and the chamfer on the oil
pump shaft will allow the oil pump to line back up. The distributor will
drop all the way back in again, with the rotor moved over one tooth. (If
it doesn’t work, try rotating the rotor the opposite direction.)
Repeat this operation (I call it “walking the distributor”) by
lifting the distributor up, slightly moving the rotor, and dropping it
back in until you’ve “walked” the rotor around to its
correct position as shown in the figure below. Once you get the technique
down, you can do this very quickly – much quicker than trying to
align the oil pump driveshaft with a screwdriver while looking down the
hole. The screwdriver technique also requires that you pull the
distributor ALL THE WAY OUT to fiddle around with the screwdriver several
times until you get it right. So try my “walking” technique:
it’s quick and accurate.
6. Once you have
“walked” the rotor into position, you should be able to obtain
the orientation of the distributor body and the rotor as shown in Figure
1. Install the distributor hold-down clamp and bolt. Snug it, but leave
it loose enough that you can rotate the distributor smoothly.
Attach an Ohm-Meter (continuity tester) between the distributor primary
lead wire (the wire coming out of the bottom of the distributor body) and
ground (any point on the engine). Rotate the distributor body SLIGHTLY
clockwise from the orientation shown in Figure 1 until you read continuity
(points are closed – giving continuity to ground). Now, SLOWLY
rotate the distributor body counter-clockwise until the points JUST break
open (loss of continuity on the ohm meter). The instant the points break
open is the ignition firing point. Tighten your distributor hold-down
bolt at this point. Your distributor body and rotor should now be aligned
like Figure 1 (or VERY close).
8. Slip your distributor cap
onto the distributor. Notice which “tower” is the #1 plug
wire. With a felt marker, place a little mark on the distributor body at
the #1 tower position. Pull the cap back off, and verify that the rotor
is pointing to this mark (or VERY close). If it’s not, you’re
most likely off by a tooth. Repeat the installation steps.
everything is aligned (and it will be if you followed these steps),
install the cap and install the plug wires as shown in figure 2.
Start the engine. It will fire and run immediately if the above steps
have been followed.
11. Set the dwell to 30 – 31 degrees
(always set dwell before setting timing. Changing the dwell changes the
Figure 1: Distributor & Rotor Correctly
Installed at #1 Firing Position
Figure 2: Correct Spark plug
Wire Order and Placement
How to Set the Timing
When you think about it, setting the timing at idle speed
makes no sense at all: You don’t operate your car at idle, and
timing changes as the rpm changes. Fact is, the timing spec at idle speed
is provided as a simple way for most people to set the timing, and is not
a good procedure for optimum performance.
Small block Chevys (and most
other GM performance V8 engines) perform best when the total timing (full
centrifugal advance plus the initial timing setting with vacuum advance
disconnected) is all in by 2,500 – 2,800 rpm and is set to 36
– 38 degrees. If you have an adjustable timing light, this is very
easy to check. If you don’t, you need to scribe a 36-degree mark on
your harmonic balancer. Here’s how:
Measure the circumference of
your harmonic balancer using a sewing tape measure (or other flexible tape
measure). Get it as accurate as you can. Take this measurement and divide
by 10. The number you get is the distance to 36 degrees. Measure this
distance CLOCKWISE from your existing harmonic balancer timing mark and
place a clear mark on the balancer.
Remove your distributor cap and
rotor. Remove the 2 centrifugal advance springs. Install the rotor and
the cap (without the springs). Disconnect the vacuum advance.
engine. It may kick back a little due to the advance coming in
immediately without the springs. If you’re using an adjustable
timing light, set the light to 36 degrees advanced. Now rev the engine
just a little while observing the timing marks with the light. It
shouldn’t take much rpm to peg out the advance without the springs
installed. With an adjustable light set at 36 degrees, align the stock
timing marks with “0” when the timing is “pegged
out.” With the non-adjustable light, align your new 36-degree mark
with “0.” Rev the engine a little to make sure the timing
will not advance any further. Shut it down.
Pop the cap and rotor and
re-install the springs. Put everything back together, but leave the
vacuum disconnected. Start it up. For future reference, make a note of
the timing setting at idle. This is your new curb idle timing spec. Now
give the engine a few quick rev’s past 3,000 rpm and verify that the
full timing (36 degrees) is coming in. If it’s not, you need to
change to a softer set of springs until you get full 36-degree advance
before 3000 rpm. (NOTE: A stock set of springs will usually not allow
full centrifugal advance to come in before redline rpm. If you have stock
springs installed, don’t rev the engine beyond its limits to try to
force full advance in.)
Shut it down and hook up the vacuum. Now
do a road test.
The 36-degree 2500 rpm advance curve is optimum for
performance, but may require premium fuel. Lug the car around, and punch
the throttle at low rpm while listening for detonation (“engine
knock”). If you’re getting any audible knock, you MUST retard
the timing. Retard the timing in 2-degree increments until engine knock
stops. Engine knock will seriously damage engine components if not
corrected. If you get no knock, you may see slightly improved performance
at 38 degrees total timing. This is particularly true if you’re
running at high altitude.
If you have no engine knock under
acceleration, but the car “chugs” or “jerks” at
cruising speed (light throttle application), you are getting too much
vacuum advance on top of the mechanical advance. You may need to change
out the vacuum advance diaphragm with an adjustable unit available from
aftermarket sources. Adjust these units so that you get the most vacuum
advance possible without any “chugging” or
“jerking” at cruise speed.
Your timing is now set for
best possible performance. Make note of the new setting, and use this for
your future tune-up work.
Porsche • GTO •