Quote:
Originally Posted by 3twinridges
Hey flathead fever, that’s interesting on the adjustable timing light. Can you explain that again? I have set a distributor on a Sun machine, by adjusting the springs, but unsure how to test that on the engine with an rpm meter and the timing light you mention. I just have a standard light to set initial timing with the distributor disconnected.
JB
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I had a hard time finding a picture of one with the adjustment knob. I guess that's old school. They are almost all digital now. Mine is a Sun adjustable timing light with the knob on the back. Here are some photos of a Craftsman one. Since our fleet was a licensed smog test and repair station the State had a list of mandatory tools we had to have. One tool was an adjustable timing light for checking total advance.
Say your timing is 4 degrees at idle on your flathead which you verify with your timing light. When the knob is set to zero the timing light works like any other timing light. You just need to remember to always set the knob back to zero hen checking the initial timing, or you will get the wrong reading. Then you raise the rpm and you will see the liming mark move away from the pointer as the timing light shows it advancing on the pulley. When you see it at its most advanced spot you rotate that knob until it brings the timing mark back in line with the pointer (were still at that elevated rpm). Rotating the knob offsets when the light flashes in degrees. By reading how many degrees you rotated the knob to bring that 4-degree mark back in-line with the pointer, plus the 4 degrees initial timing, you will know your total advance. I don't know how accurate it is compared to a distributor machine, but I bet its close.
We used it to independently check the degrees of mechanical advance the centrifugal weights made by raising the rpm, with the vacuum advance disconnected. Then at idle, when the weights were not working, we applied a handheld vacuum pump to the vacuum advance and checked its amount of advance. Then you raise the rpm with a vacuum gauge on the hose to the advance unit and make sure the vacuum advance is getting the correct vacuum signal. Many of those units are adjustable using an allen wrench through the vacuum hose hole so you can dial it in exactly to the factory specs. Same with changing the springs on the weights. You can make the advance come on sooner or later using weaker or stronger springs. Using a tachometer and that adjustable timing light you can tell how much advance at what rpm you are getting. I wish I could have found a video showing one in use and then it would made more sense.