Tdc

[Whymelaugh13]

When ajusting your distributor cap, how do you know the #1 piston is in TDC? If its at the top couldnt it just be bewtween the exhaust and intake strokes?

[ivymike1031]

what do you mean by "when adjusting your distributor cap?" What kind of adjustment are you doing?

You can tell whether any piston is at TDC compression or TDC exhaust by looking at the position of the cam.

[jimmymc]

Top dead center usually refers to the #1 piston being at tdc on the compression stroke. The piston also comes to the top on the exhaust cycle in a four cycle engine.

To properly align your distributor it is necessary to determine tdc on the compression stroke, because this is when you want that spark plug to fire.

If you are looking at the cam or rocker arm...when the intake valve closes the next time the timing reference mark comes up will be tdc on compression stroke.

There are also other ways to determine this...

jimmymc

[ivymike1031]

I just had a thought - you aren't trying to set your ignition timing, are you?

[Moppie]

Two ways, either find the mark on the crank pully, or flywheel (depending on your car) of if you can't see it, take out the No1 spark plug and rest a light metal or wooden rod in the hole, then turn the engine gently by hand untill its sticking as far out of the hole as it will go.

[ivymike1031]

that's gonna get you to TDC, but the poor guy wants to know whether it's TDC exhaust or TDC firing (have to check the cam/valves position)

[Moppie]

Well it should be marked on the crank pully, and then use the above to get it exact.

But you can always hand screw a spark plug back in, and feel it when it comes up to the compresion stroke, or even easier take a look at the Rotor position in the Dizzy.
It will be pointing at the lead for No1 when its on the firing stroke.
(Unless of course the dizzy is on 180 degree out, then you have a whole lot of other problems).