Which way is the zero of pulley timing mark on 240z?

[tamo3]

Hi,

I just got Xenon Timing Light to measure ignition timing.

When I look at pulley timing mark, I can't tell which side is zero since it's different from 280z timing

Is top one the zero or the bottom one in the picture?

When I look at FSM for '72 240z said "The top dead center is located extreme left as viewed from inspectors side."

Thanks for the help,

tamo3

[Zed Head]

If you connect the light, start the engine, and rev it up, the pointer will move away from the zero mark, crossing the other marks as it moves. I'm not familiar with the 240Z marks, so can't say if the marks start at zero though. On the 280Z, there is a negative five degree mark.

[beermanpete]

The zero mark will be the top mark or the second mark it there is a -5 mark.

The best thing to do is verifiy the zero mark physically and mark it with a bright color such as a white tire crayon. china marker, or paint. Take the #1 spark plug out and turn the engine by hand until the timing marks are near the pointer. Now you can place a thin probe (a long thin screwdriver works sell) through the plug hole into the cylinder. While turning the engine (by hand) hold the probe so it touches the top of the piston and feel it move with the piston. When the engine is at TDC the pisotn will seem to stop moving for a moment while you are turning the engine. Turn the engine back and forth slightly to get as close to TDC as you can. Without moving the engine, mark the edge of the pulley with the crayon or paint. Unless the balancer is bad TDC will correspond to one of the timing marks on the pulley.

[tamo3]

Thanks so much for the advice.

I was lazy to avoid open valve cover and check TDC.

In order to get accurate TDC with pulley mark, I understand what I got to do.

FYI

I try to install 280z timing mark plate onto 240 P30 block, but the screw location is slightly different from N42 block.

[Jarvo2]

Zero is the bottom dash on your photo above. When you rev the engine, timing will 'advance' and move up the marks.