How To Verify Your Valve/Crankshaft Timing &
Set A Distributor.
If you don't have a good working knowledge of shop safety practices, DON'T ATTEMPT THIS!
If you don't possess common sense or self preservation instincts, DON'T ATTEMPT THIS!
Safety warnings are in RED, Do Not Ignore These!
I can not possibly list all the potential ways you can get hurt doing anything you read or see
here, so YOU MUST ASSUME ALL RESPONSIBILITY FOR YOUR SAFETY!
ALL STEPS REQUIRED, DO NOT SKIP ANYTHING OR THE RESULTS WON'T BE ACCURATE
Finding The #1 Cylinder
The #1 cylinder is the first to fire in your firing order
(more on firing orders, click here).
If you are working on an Inline engine (all the cylinders in a row) the #1 cylinder will be the
first one, closest to the radiator.
If you are working on a 'V' style engine (V-4, V-6, V-8, V-10), one cylinder will be farther
ahead of the rest.
Look to see which cylinder head is closer to the radiator, and the front cylinder that will be
Finding Top Dead Center (TDC).
Disconnect the ignition coil before cranking the engine.
Take out the spark plug of the #1 cylinder.
Cover the #1 spark plug hole...
Use a Lightly pushed in cork or other relatively soft item that won't react badly with
DO NOT stick your finger in the hole, only cover it.
Compression on modern engines is sufficient to remove your fingernail and infuse gasoline into
Crank the engine over until the cork is pushed out. IMMEDIATELY STOP CRANKING!
Locate the crankshaft snout bolt, You will find this bolt in the center of the lower pulley.
Place your finger OVER the hole, and crank the engine clockwise with a hand ratchet by the
crank shaft snout bolt.
Removing the other spark plugs may make this task easier. Resist the urge to use the starter...
You will feel the compression stroke start even when cranking by hand.
When you feel the compression stroke start, use a 1/4" wooden dowel rod (wooden chopsticks work
well) to feel for the top of the piston through the #1 spark plug hole.
DO NOT USE METAL LIKE A SCREW DRIVER!
You want to use the dowel rod and the crankshaft to locate the piston at the very top of the
It is possible to have the piston at the top, and still not have 'Compression Stroke'.
The crankshaft rotates two complete revolutions for each time the #1 cylinder fires.
The strokes are,
'Intake Stroke', when the piston is going down with the intake valve open, drawing Charge Mixture
(gasoline & air) into the cylinder,
At the bottom of the 'Intake Stroke', the Intake Valve closes, and the
'Compression Stroke' starts.
The piston comes back up with both valves closed, and compresses the Charge mixture, this is
the 'Compression Stroke'
This is the stroke you are looking for Top Dead Center (TDC) of.
The cylinder contents are compressed, then the ignition fires when the piston is more or less
at the top.
Expanding gasses drive the piston down, this is the 'Power Stroke'.
When the piston reaches the bottom of the 'Power Stroke', the Exhaust Valve opens, and the
piston comes back up, pushing out the spent gasses.
As the piston rolls over the top of the 'Exhaust Stroke', the exhaust valve closes, and the
intake valve opens starting the process again.
(Suck, Squeeze, Bang, Blow)
As you can see, it is very possible to find the top of the 'Exhaust Stroke' instead of the top
of the 'Compression Stroke' you are actually looking for.
Once the piston is at Top Dead Center (TDC) of the 'Compression Stroke'...
Verifying The Balancer & Timing Tab
So Called 'Harmonic Balancers' is mounted behind the lower engine pulley, and have a solid hub,
usually cast iron, a layer of rubber, and a steel ring on the outside.
The 'Timing' mark is usually on the outside of this steel ring.
There should be a 'Timing Tab' or 'Timing Marks' mounted on the front of the engine that
Now, if everything is working correctly, the timing mark on the balancer should be lined up
with the '0'(zero) mark on the timing scale.
Things that can go wrong are,
The outside ring of the balancer will break free of the hub and slip around the hub, causing
the 'Timing Mark' to be in the wrong place.
The 'Timing Tab' can get bent, damaged or completely removed. Also, if the engine has been
'Rebuilt', it's not unusual for the wrong front cover and/or balancer to be put back on.
Some engines required an offset key to hold the balancer in the correct position, if that key
has been replaced, it may not be the correct one.
Aftermarket parts (like chrome parts) are often, "One size fits all..." and are not appropriate
for your engine.
If you have found the top of 'Compression Stroke', and verified the balancer and timing tab,
you are ready to set the new distributor in place or verify the timing of your current
Verifying An Existing Distributor
(If you are installing a new distributor, skip to the next step.)
Use a 'magic marker' and mark the position of the #1 spark plug wire tower on the base of the
distributor and remove the distributor cap.
If you have the piston at the top of the 'Compression Stroke' on the #1 cylinder, the Rotor
nose should be pointed at the mark you just made on the distributor body (within a few degrees).
If the rotor pointed exactly away from the #1 mark you made, then one of two things is probably
1. You located the top of the 'Exhaust Stroke' instead of the 'Compression Stroke',
2. Your distributor is installed '180° Out'... (this is very common on inline engines)
If your Rotor nose is anywhere else, you need to start over and VERIFY EVERYTHING...
It's possible for the gear to be installed incorrectly on the distributor shaft, it's possible
for timing chains to have stretched and jumped teeth, it's possible for distributor to camshaft
gears to be so worn they will 'jump' teeth, ect.
Installing The Distributor
Distributors have sprial cut drive gears, so the distributor shafts rotate when installed as
the distributor gear moves around the stationary camshaft gear.
To Compensate for this, you will have to know what direction the distributor rotates, what your
firing order is, where #1 plug wire is supposed to be located, and mark that location on the
1. To determine rotation direction, vacuum advance always pulls against distributor rotation,
2. #1 plug wire tower is usually marked on good quality distributor caps, if not,
Install the rotor and distributor cap on the distributor and mark the location of the #1 plug
wire terminal and direction the rotor travels on the distributor base.
Remove the cap, but leave the rotor in place.
Now, back the rotor nose against rotation about half way between terminals. This would be
last terminal fired, and the #1 terminal.
Drop the distributor in the hole until the drive gears meet. DO NOT FORCE THE DISTRIBUTOR
Most distributors will NOT engage fully when dropped into the hole.
The problem is the oil pump drive shaft is turned by the bottom of the distributor gear, and
the two pieces will not line up on the first try.
To get the distributor to seat fully, you will have to rotate the engine BY HAND, TWO COMPLETE
REVOLUTIONS, while putting some down pressure on the distributor (don't push hard).
The distributor may drop into place in just a few degrees, but you will have to make TWO
COMPLETE REVOLUTIONS of the crankshaft to bring the engine back to Top Dead Center of the #1
cylinder determined by the timing mark and timing tab you verified earlier.
Resist the urge to turn the engine backwards, always turn the engine clockwise (top of the
crankshaft pulley towards the drivers side fender). Turning backwards is VERY hard on crankshaft
Once you have seated the distributor housing and found TDC of #1 again,
Check to make sure the vacuum advance canister is in the correct location, and check the rotor
nose in relationship to the mark you made on the distriburor housing.
If the rotor nose is pointing (within about 5° or so) at the mark, you are ready to install the
distributor cap and plug wires.
If the rotor nose is NOT pointing at your mark (half way between terminals, too far ahead, too
far behind) you will need to pull the distributor and try again, compensating for the alignment
problem. (farther forward or backward in the rotation.)
Smaller diameter drive gears (GM, AMC for example) tend to need more rotor rotation before
install, and larger diameter drive gears (Ford for example) tend to need less rotor rotation.