Installing Plug Wires When the Crankshaft and Valvetrain Are in an Unknown Position

By Bill Thebert

A large number of problems seem to arise when shadetree mechanics remove ALL of the plug wires, and then attempt to re-install them from scratch on a motor with the crankshaft and/or valvetrain in an unknown position. This is often the case, for example, after a rebuild.

Following is a procedure that I originally wrote for installing ALL spark plug wires onto an IHC V8 from scratch (since that is primarily what I work on). But I have modified the procedure to make it sufficiently generic to be applicable to other makes.

First, you need to know for sure which cylinder is used to TIME the motor. Don't presume that you know. Most Chevy motors use cylinder #1, for example. But IHC V8 motors, in contrast, are timed from cylinder #8. Also be sure that you know which cylinder is which. Typically cylinders are numbered from front to back, in the order in which the connecting rods are sequenced on the crankshaft. In the case of V6, V8 or V10 motors, this typically puts all of the odd-numbered cylinders on one side of the block, and all even-numbered cylinders on the other.

1) Remove the spark plug from the cylinder used to time the motor. (Reminder: Chevy = #1; IHC = #8) In the case of IHC v8 motors, this is the rearmost cylinder on the passenger side. (Four-cylinder IHC engines: use the #1 cylinder.)

2) Have a friend slowly rotate the engine by hand using a ratchet or a breaker bar and a socket on the front end of the crankshaft. Be sure to rotate the engine in its normal direction of operation. Now is a good time to observe the distributor rotor to see which direction it is rotating (clockwise or counter-clockwise) as the engine is being turned.

Here comes the most important step -- the step where most errors occur.

3) Place your thumb over the now-empty spark plug hole as you observe the timing mark on the balancer. AS THE MARK APPROACHES TOP DEAD CENTER (TDC), you may or may not observe pressure building under your thumb.

If you do observe pressure, the cylinder is on the compression stroke, and you should stop the engine with the timing mark at about 5 degrees BEFORE TDC.

If you do not observe pressure under your thumb, it's because the cylinder is on the exhaust stroke, and the exhaust valve is open. Rotate the crankshaft one entire additional turn, until the timing mark again approaches TDC. You should feel pressure now.

Many shadetree mechanics simply forget that the crankshaft goes around TWICE for every combustion cycle in a given cylinder. They assume that the sparkplug should fire every time the timing mark is at TDC -- when in fact this is only true HALF of the time.

4) Now that you've verified that the timing cylinder is on its compression stroke, and you've set the crankshaft to 5 degrees BTDC, identify the distributor cap TERMINAL at which the distributor ROTOR is currently pointing. Rotate the distributor slightly (as if you were adjusting timing) if necessary to get the rotor pointing DIRECTLY at any given terminal.

5) Attach the timing cylinder's spark plug wire to the terminal identified in Step 4. (Reminder again: Chevy = #1; IHC = #8) Continue attaching plug wires in the direction around the distributor cap that you identified in Step #2 above. (IHC distributor rotors turn in a CLOCKWISE direction when viewed from above.) Follow the firing order that is found in your service manual, and which is sometimes cast or stamped into either the intake manifold or a valve cover.

For example, the firing order on an IHC V8, starting from the #8 timing cylinder, is as follows:

8-4-3-6-5-7-2-1

The first wire (after the engine was properly positioned in Step #3) goes from the #8 cylinder to the distributor cap terminal at which the rotor is currently pointing. The next cap terminal CLOCKWISE from there gets wired to the #4 cylinder. The next one to the #3 cylinder, etc.

Owners of IHC 4-cylinder motors should start with Cylinder #1 and use the following firing order:

1-3-4-2

6) The engine should now be close enough so as to be able to be started, and the timing adjusted using conventional methods.

DISREGARD ANY MARKINGS THAT MAY BE FOUND ON THE DISTRIBUTOR CAP. Many Ford distributor caps, for example, have the number "1" molded into them. This does NOT signify the location of the #1 plug wire. Most distributors can be installed into their respective motors in as many different ways as the drive gear has teeth. Conceivably, *any* terminal on the cap can be made to be #1.