The timing mark comes up twice- - - - -once when the cylinder is on compression, ready to fire the gas, and again when it's between exhaust and intake. That's how people get the dizzy in 180 degrees out of time. #6 is the companion cylinder to #1, so when the #6 valves are on the overlap position, intake opening/exhaust closing, #1 is definitely on compression, ready to fire the plug. It also works on a stovebolt, with #1 and #6 as companion cylinders.
Jerry

Edit: To find the companion cylinders on any engine with an even number of cylinders, cut the firing order in half.

Any I-6:
1-5-3-6-2-4- - - -becomes
1-5-3
6-2-4

1 & 6 pistons come to the top at the same time, one on compression, one on overlap. Ditto for 2 & 5 and 3 & 4. This also works for doing an accurate engine-stopped valve adjustment.

V-8: 1-8-4-3-6-5-7-2

1-8-4-3
6-5-7-2

Simple and easy to remember.
Jerry

Last edited by Hotrod Lincoln; 11/22/2008 4:34 AM.
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