Tech Articles

How to Use a Dial-Back Timing Light

(Image/Jeff Smith)

It’s a sign of the times when late model engines with distributorless ignition systems (DIS) no longer require the services of the ubiquitous timing light. But for the remainder of the performance world that does rely on distributors, a timing light is an essential tuning device.

Over the course of decades of technical writing, we’ve discovered that not everybody understands how a timing light functions and the insights it can offer on the state of tune of your engine.

We’ll start with the basic light and then move on to the more sophisticated dial-back versions and how they function. A simple timing light is really nothing more than a stroboscope designed to flash when triggered by the spark from the engine’s Number one cylinder.

That stroboscopic flash is intended to ‘freeze’ the location of the timing mark on the harmonic balancer relative to a timing tab usually attached to the engine’s front timing chain cover.

In the old days, all timing lights used a small spring that fit between the spark plug and the plug wire that was connected by a clamp to send a high-voltage trigger to the light. Your grandfather might have one of those lying around his shop. All guns today use an inductive pickup that surrounds the plug wire and picks up the electro-magnetic energy that surrounds the plug as the voltage passes through the plug wire.

Timing lights can be described in a number of ways, so let’s go over that with a short description of each. The simplest timing lights are self-powered. These lights use batteries in the body of the light that amplifies the signal from the inductive pickup on the plug wire. The most common form of timing lights powered by a simple pair of clamps hooked to a 12-volt battery source.

The next level up from a basic timing light is what is called a dial-back light. These timing lights use electronics to delay the onset of the spark based on how much delay is dialed in on the light. Original dial-back lights used a simple dial with a timing scale.

The more sophisticated electronic dial-back lights offer a digital screen usually at the back of the gun that will display rpm and the amount of timing delayed. Upscale versions will also display battery voltage.

Before we get into how to use a dial-back light, we should run through why they are needed in the first place.

Most engines use a timing tab that is welded or bolted to the front timing chain cover. The tab will offer several hash marks indicating the number of degrees of timing before top dead center (BTDC). These tabs can also display timing after top dead center (ATDC). Sometimes the tab will be marked with a ‘B’ for before and ‘A’ for after. A does not mean advanced — in fact, ‘After’ is the exact opposite. So be aware of this.

If you want to set initial timing at something more than 10 or 12 degrees indicated on the tab using a traditional timing light, this becomes a guessing game. Plus, you may also want to know what the total mechanical advance is and at what rpm it occurs. This can be done with a degreed balancer, but these are expensive.

MSD offers a series of adhesive tapes for each popular balancer diameter which are accurate enough to use in lieu of a dial-back light. All you do is line up the zero mark on the timing tab with the hash mark on the timing tape to determine the timing.

As an aside, if you are in a position where you are in immediate need of a timing tape but one is not available, you can make one using a length of masking tape, a straightedge, and a dial caliper.

For example an 8-inch balancer circumference is Pi x diameter or 8 x 3.1417 = 25.12 inches.

To create two-degree marks would be 25.12 divided by 180 = 0.1396 — round that off to 0.140. Make a mark every 0.140–inch from the zero mark and you have your own backyard timing tape. Just line up the zero mark on the tape with the zero mark on the balancer and remember which way advanced timing will be positioned on the balancer so you don’t put it on backward indicating retarded timing.

A dial-back light saves all this effort. These lights are great for working on multiple engines that do not have degreed balancers or timing tapes. Most all dial-back lights are now electronic but there are a few that still employ an analog dial for the more traditional hot rodders.

The one we’re using for this discussion is an Innova electronic dial-back light. It connects just like any other light and uses buttons to advance or retard timing. The digital display on our light will indicate amount of timing and engine rpm. The tach is a great feature that is also useful for setting idle speed. The pro version will also display battery voltage.

Dial-back lights operate by delaying the light flash by the number of degrees indicated by the dial or on the digital display.

Let’s say the engine requires 15 degrees of initial timing at idle. With the engine running, merely press the advance button on the Innova light to advance the timing until the zero mark on the harmonic balancer lines up with the zero mark on the timing tab. The amount of timing displayed on the light is the initial timing.

Next, if you want to check total mechanical advance, first unplug the vacuum advance canister from the carburetor. This will prevent vacuum advance from affecting the mechanical advance reading. Make sure the transmission is in Park if an automatic or Neutral if a manual transmission and the wheels are chocked. Rev the engine carefully to achieve the rpm where the timing stops advancing. Push the advance button on the dial-back light (or turn the dial) until the zero mark on the balancer lines up with the zero mark on the timing tab. You will see a number ranging from 32 to 40 degrees, which would be the total of initial plus the mechanical advance.

There are a couple of more sophisticated ways to use a timing light for more advanced ignition timing tuning, but we’ll save those for another time.

If you’re just getting started on working with older engines, a timing light is one of the first items that should be part of your basic tool collection.

Here is a layout of several different timing lights. The small cylindrical light is a Flaming River self-powered gun with an inductive pickup that uses D-cell batteries for power. The red light in the upper left is a self-powered unit from MSD that is handy when there is no convenient battery connection. The chrome light is a powered MSD unit that is a non-dial-back that has been replaced with a red version. Finally, the light in the upper right is an Innova electronic dial-back light that is our new favorite. (Image/Jeff Smith)
A powered timing light will require 12-volt power from the battery with positive and negative clamps on the battery and then a trigger connection using the inductive pickup around the Number One spark plug wire. Sometimes these pickups require proper orientation by indicating the direction of the spark plug to ensure the pickup works properly. (Image/Jeff Smith)
(Image/Jeff Smith)
Any timing light will flash when the Number One spark plug fires. This stroboscope flash will “freeze” the timing mark on the balancer relative to the timing tab. In this case, the mark lines up with 10 degrees Before Top Dead Center (BTDC). Because the crankshaft and harmonic balancer turn clockwise and the tab is located on the driver side of the engine, timing BTDC will be displayed above the zero mark. If the tab was located on the passenger side, the BTDC numbers would be below the zero mark. (Image/Jeff Smith)
Traditional dial-back lights used a simple dial on the back of the light. Rev the engine, and twist the dial until the timing mark lines up with the zero mark on the tab. (Image/Jeff Smith)
It’s not necessary to purchase a dial-back timing light just to read the advance on your engine. MSD sells this timing tape card with clearly marked timing numbers that are specific for various diameter balancers. This is required because the spacing of these marks will change with the diameter of the balancer. (Image/Jeff Smith)     
Here is an MSD timing tape on a small-block Chevy where the zero mark on the tab is just a notch in that tab. We’ve marked 36 degrees on the timing tape to help find our total timing when we rev the engine with a dial-back light. (Image/Jeff Smith)
Here we’ve aligned the zero marks on our timing tab and balancer indicating 15 degrees of initial timing on our carbureted small-block Chevy. Also note that the idle speed is 819 rpm at this moment. (Image/Jeff Smith)
Revving the engine up to where the total timing is all requires quick work since you don’t want to park the engine at 2800 rpm or more for very long. Here, we measured 34 degrees of total timing at 2860 rpm. (Image/Jeff Smith)
Tags: , , , ,

4 Comments

  1. Pingback: How to Use a Dial-Back Timing Light

  2. I am a reminder so I know a lot of this stuff.
    BUT this article was a very good idea, for the young generation whith computerised cars. Maybe and hopefully, they some day meet and buy one old “real” car.

    Regards

  3. I’m an “Old Timer” and still use a timing light especially if I put a new timing chain set up ( chain gears etc) Then your 100% on. As far as the marks on the harmonic Balancer?,Bring the Engine to TDC,Mark the balancer,Start the Engine,Zero in on that mark, Turn the Distributor until the Engine evens out, take a picture with cell phone mark that position and your done.Ive seen all different ways from all types of mechanics some good:some bad! This always worked for me. THAT’S OLD SCHOOL.

  4. Pingback: Stuff from D. July 13th, 2020 – Darryl's Drive In

Leave a Reply

Your email address will not be published. Required fields are marked *

*

This site uses Akismet to reduce spam. Learn how your comment data is processed.