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Wed Sep 07, 2011 2:08 pm

today i started adjusting the valves in my 72 bus, but as i lined up the line on the crankshaft pulley and the zero mark, and lined the distributor rotor up with the notch to bring it tdc, i tried to adjust for cylinder one but it was in the middle of firing so the valves were not closed. After a while i decided to try and adjust the valves that looked like they were closed, i rotated the engine over and adjusted for all 4 but when i started it mad the clack of too large a gap. How can i find TDC and do this accurately?

Wed Sep 07, 2011 3:20 pm

You mostly had it but not quite.

Take the cap off the distributor but know in what position your #1 plug wire is. Rotate the crank until the pulley mark is aligned at the zero mark on the timing scale. If the rotor is pointing generally towards where the #1 wire was then that's the correct spot to adjust #1 valves. If the rotor isn't pointing towards where #1 wire was then rotate the crank pulley 1 revolution CW to the pulley zero mark and the rotor should now be towards #1 wire location. Then you can adjust #1 valves.
Then put another mark on the pulley exactly opposite (180 degrees) from your main pulley mark. Turn the crank 180 degrees CW until your new mark is at zero. You will see that the rotor is pointing towards where #4 plug wire was so then adjust #4 valves. Then turn the crank another half turn CW to the original mark and the rotor will point to #3 wire so adjusst #3 valves. Then another half revolution to 2 and adjust #2.

Another way to look at it and understand it is put on a pulley mark exactly opposite the original pulley mark. Then whereever you turn the crank to get either of the marks to line up with zero the look to see which plug wire the rotor is point towards. Which ever one then go adjust those valves.
that new mark you made just call it 180 degrees. When the 180 degree mark is aligned at zero then that's the place where you adjust either #4 or #2 valves, depending on where the rotor points. When the original pulley mark is aligned at zero then either #1 or #3 can be adjusted, depending on where the rotor is pointing.