Time after Time

I spent several hours leaned over the bow, the rest perfectly centered the arrow, right where it had to be. The nock point was exactly where I like it. The arrows were rotated so that the fletchings would easily clear the rest. Everything was tightened and in place. The bow was ready.

The first shot through paper should have been a formality, but it wasn’t. Three hours later I was still scowling at a paper tear the likes of which I’d never seen before. I noticed a hammer in the corner; I leered back toward my bow. No, that would be too easy.

The nock of the arrow was passing through the sheet of test paper fully five inches below the point. I could have gotten better flight throwing the arrow.

Nothing I tried had any effect. Then it struck me; what if the wheel timing was off?

It was off, all right—way off. The bow had felt jerky near the completion of the draw, an obvious indication of improper timing, but I was inexperienced and the symptoms never translated. Six twists to one of the synthetic harnesses were all I needed to produce a tiny shaft-size hole in the paper with the very next arrow.

Easy to Master
Wheel timing is the one aspect of tuning a two-cam bow that even many advanced bow mechanics overlook and is one of the primary reasons single-cam bows have become so popular. Before you will ever produce good arrow flight with your two-cam bow, you need to be able to check and set your cam timing. Thankfully, the process is not hard to master.

Your cams are supposed to roll over at exactly the same moment so they hit the back of the full-draw valley together. When they don’t, the solution always boils down to one thing: The harnesses aren’t the same length.

Take note of where your harnesses or cables are attached to the bow. One end is grounded to each axle, usually through a split yoke system. The other end is attached to the opposite wheel and is wrapped partially onto the harness track.

Assume one harness suddenly stretches an eighth of an inch while the other remains the same length. Now the cams are in different positions and the bow is out of time. The wheel attached to the longer harness is essentially ahead of the other; when the bow is drawn, this wheel will get to its full draw position first. (Understand that we are talking about the harnesses, not the string. Changes in string length may affect accuracy and tuning, but they have no effect on wheel timing.)

Fast Flight harness systems can lengthen from exposure to heat, high levels of moisture and from normal stretch associated with breaking in the bow. A break-in period is usually required with any bow. Usually 300 shots will set any synthetic, especially if heat and moisture are also encountered. Allow that many arrows before making final adjustments to your rig.

Timing Check
Before you can accurately check your timing, you need a precise reference point. You can mark the wheel with a wax pencil or something similar to indicate a position relative to the limb. If the wheel is a hard cam, this method may not be precise enough; even one twist in a synthetic harness can shorten it enough to produce a noticeable difference in arrow flight.

The most accurate reference point I have found is to compare the harnesses to the end of their respective tracks just as the cams reach their full-draw positions. The harnesses of both wheels should touch down on the end of their grooves at exactly the same time.

The harness or cable attached to the wheel that reaches the end of draw first must be shortened. Some bows that were produced in the past had micro-adjustable yoke systems to make timing the wheels a snap, without having to relax the tension on the bow. If your bow is not so equipped, you will need to twist the longer harness (the one attached to the cam that’s “ahead”) in the direction of its spiral to shorten it. Older steel cables can be shortened in this manner as well.

To remove the end of the harness from its attachment post on the cam, you need a bow press. Most pro shops have bow presses that can be used for this task, but if you are serious you need one of your own. Pool your funds with a buddy or two and buy a good bow press. They’re handy for a lot of bow-maintenance tasks.

After relaxing the tension on the string and harness system, simply remove the longer harness from its attachment point on the cam and give it one or two twists to shorten it before replacing. Check the timing again. Repeat the procedure until the wheels are perfectly timed.

Improper cam timing affects arrow flight in dramatic fashion—causing tail-high or tail-low tears through your test paper.

Never assume that your timing is acceptable; check it often. If wheel synch should change even slightly during the hunting season, your accuracy with broadheads will be affected. One of the final steps in mastering any two-cam bow is to understand, monitor and correct cam timing. Now you know how.