jackson 63

On my 63 340HP engine the timing tab has a A and a O on it. What does the A and O stand for? My car calls for 10 deg before top dead center, could someone tell me where that is on the tab. Thanks

rongold

The "0" represents zero degrees and the "A" represents 10 degrees. Each small mark on the tab represents 2 degrees. The tab should go up to either 16 or 18 degrees total if I remember correctly.

LB66383

The O stands for zero, or top dead center. The A stands for Advance, the number of degrees of ignition advance that it was set to -- that's with the vacuum advance disconnected. There should be some other markings on that tab between the two. Each marking is two degrees of timing. Yours should have four of them.....2, 4, 6, and 8 degrees. The A is at 10 degrees.

Powershift

When initial advance is set, the vacuum advance (if installed) hose needs to be disconnected and plugged, and the engine RPM needs to be below 700 RPM. That way there is no vacuum advance or centrifugal advance "active" during the initial timing setting.

Then, if possible, run the engine RPM up to see what the maximum and final "initial + centrifugal advance" is for the engine. Also called Total Mechanical Advance. It should be 36-40 degrees for the small block Chevy engine. You would like it to be "all in" at around 3000 RPM, but for some engines it is not until close to 5000 RPM. It just depends on the distributor. But the 36-40 degree TMA number is the same for all.

You will need a "dial-back" timing light or you must mark/index the timing balancer to read these higher numbers.

When finished, reconnect the vacuum advance (if equipped) and reset the idle speed.

Larry