Tdc

[philip j]

If #1 cyl is TDC, what exhaust valve should be open. Philip

[hcoles]

could be more than one slightly or more open, including #1 cyl

[philip j]

Looks to be fully open, the rest it's hard to tell, but #6 has considerable difference

[lindy 911]

If you're trying to set the dizzy rotor, turn the crank while watching the #1 exhaust valve. When it opens and then starts to close keep rotating the crank until the Z-1 mark. Now go around one full turn to Z-1 again. At this point you will be on the fire stroke of the #1 cylinder and the rotor should be pointed at the #1 plug wire in the cap...

[Bob Kontak]

You can think this through.

1 6 2 4 3 5

tdc AT #1

Both valves closed

#6 is 120 degrees behind

It's on it's way into the compression stroke so exhaust is closed and intake is closed or just about to.

#2 is 240 behind and is on the intake stroke

It is sucking in air/fuel so exhaust is closed and intake is open.

#4 is at overlap TDC (360 behind) and just finishing up the exhaust stroke

Depending on cams both could be a little bit open with exhaust to close and intake to open

#3 is in the exhaust stroke (add 120 degrees)

Intake closed and exhaust open

#5 is on the power stroke

Intake closed and exhaust just about to open

[lindy 911]

There are TWO top dead centers for each four strokes. The above assumes TDC at the compression stroke. None of it works if it's TDC at the exhaust / overlap stroke.

[Bob Kontak]

Originally Posted by lindy 911

None of it works if it's TDC at the exhaust / overlap stroke.

Best way to tell is to make sure your distributor rotor is pointing at the number one spark plug wire terminal when the Z1 mark lines up.

It's easy - but as always - once you get the hang of it.

[philip j]

She fired right up after turning 180*. New motor with twin plugs. Custom dizzy, so no marks. Any way I got it to run for the 20 min breakin @ 2000 RPM. Thanks for the help, and yes Bob, # 4 exhaust was were you said it would be. cheers Philip