How to make a timing tape
Making a semi-permanent timing tape is very easy. It replaces the need for a "dial back" timing light and removes any doubt as to where the timing marks are correct or not.
You need to know (or verify) that the TDC or "0" degree line on the damper or balancer (henceforth to be called a "damper") and the timing tab or mark actually correctly represents "0" degrees (TDC). On the SBC for example, there are three commonly encountered timing tab/damper lines that can be mismatched, causing an incorrect reaing. More on this at Timing tabs and damper lines SBC.
One method to find TDC is by using a piston stop and fabricate a timing "tab" (often a stiff piece of wire secured behind a convenient bolt head) that aligns with the line on the damper to represent "0" or TDC. Help with this can be found at Determining top dead center.
Once TDC has been established, the rest goes like this:
- Using either a string, ruler or a seamstress' cloth tape measure, measure the circumference of the damper. If you only have a straight ruler, measure the diameter and multiply by 3.1416 (pi) to get the circumference.
- Once the circumference is known, 1/10 (10%) of this figure represents 36º. Half of that is 18º, half again is 9º, etc. It doesn't matter what units are used to measure the circumference- metric, inch, or nanoparsecs.
- If you want to use the metric system, multiply the circumference by 25.4 to convert to millimeters. Divide this by 360 and you'll get the measurement in millimeters that equal one degree.
- Careful measurement and marking of the degrees in this fashion on a length of masking tape can then be applied to the damper, aligning TDC or "0" on the tape to the line on the balancer, with the degrees BTDC to the right of this mark.
- You can also measure the length between the timing tab marks and transfer them onto tape, i.e. if there's 3/4 of an inch (0.750") representing 10º on the tab, two marks 3/4 of an inch (0.750") apart on your tape will also be 10º. This will work- provided that the timing tab is correct for the application and not for a different diameter damper.