A Slip of the Balancer
Joe Schneider, Phoenix, AZ: I thought you might be able to help me with my small-block Chevy problem. I recently built a 355 to run in a '57 Chevy. During break-in on the new engine, we could not get the timing marks to line up. We set the timing by ear so that the starter motor would turn the engine over normally and not get hung up from overadvanced timing. I have an aftermarket timing pointer bolted to the engine. I checked the balancer to verify that the outer ring had not slipped by comparing it to a new balancer to determine the keyway position to the timing mark. I know about the approximate 9-degree shift in the timing-pointer position by Chevrolet, and this does not appear to be the cause of the problem. Any insight would be helpful.
Jeff Smith: The original Gen I small-block Chevy has seen three different timing locations on the balancer. Pre-'69 engines located the top dead-center (TDC) mark about 2 degrees counterclockwise from the balancer keyway. In '69, Chevrolet moved this TDC mark to roughly 10 degrees counterclockwise before the keyway. The final change in '86 moved the mark to 40 degrees away from the keyway. Let's assume that you have a balancer with the most common 10-degree position. If your aftermarket pointer happens to be set up for the older 2-degree position, this could account for most of the discrepancy. Unfortunately, we don't have enough facts to make a clear distinction, so we're guessing. However, we do have a simple fix that can be applied to any engine where this is a problem.
The key is to establish an accurate TDC position on the balancer. This may involve making your own pointer or creating a new TDC reference point on the balancer. Either way will work. This procedure will require a piston-stop tool, which you can buy from almost any performance outlet. Summit Racing sells one for a mere $6.95 (PN SUM-900189), or you can make one out of an old spark plug and a long bolt. First, yank all the spark plugs and put the trans in Neutral or Park if it's an automatic. With a ratchet or long breaker bar, rotate the crank clockwise with the piston stop screwed into the No. 1 cylinder (driver-side front). Gently turn the engine until the piston hits the stop. Mark the balancer with a felt-tip pen or chalk using the 0 mark on your timing tab. Next, rotate the engine counterclockwise until the piston hits the stop, and record this position on the balancer in the same fashion. Remove the piston stop and rotate the engine over until you can accurately establish exactly halfway between the two marks on the balancer. This is your true TDC position for your engine. This is the only TDC mark you should use to reference ignition timing.
If you don't have a dial-back timing light and would like to know how much total mechanical advance the engine has, you can use some simple math to create your own custom marks on the balancer. You mentioned that you are using an 8-inch balancer. If we multiply 8 by Pi (3.1417), this equals circumference (8 x 3.1417 = 25.13 inches). If we divide this distance by 180, it gives us 0.1396 inches (or roughly 91/464 inch) for every 2 degrees. We can now use multiples of 2 degrees to mark the balancer. This means that 10 degrees would be 0.698 inch (or roughly 451/464). For 36 degrees, multiply 0.1396 by 18 (2.51 inches). You can use a thin steel rule graduated in 64ths of an inch to mark your balancer accordingly. Or if you have a dial caliper, lay a length of masking tape and establish a TDC mark, then use the dial caliper to produce the necessary marks at any position you prefer. This will also be more accurate than trying to read a steel ruler. Remember that to check for total mechanical advance, you need to disconnect the vacuum advance or the total will indicate the combination of mechanical and vacuum advance. If you don't want to go through all that drill, you can buy timing tapes that are already graduated for your diameter balancer from MSD (PN 8985, $4.88 from Summit Racing). Just be sure to use the correct tape for your diameter balancer.
Use masking tape and a dial caliper to establish the proper positions for 10-, 16-, 20-, 30-, and 36-degree increments. Then place the tape on the balancer and you're ready to go.