Finding TDC (Top Dead Center)

Last updated: June 05, 2000

From: Carlos Iglesias
Date: September 18, 1999

FINDING #1 ROTOR TDC (2 rotor only)



  1. Remove both plug from the #2 (rear) rotor housing.

  2. Get a mirror and light source positions that allows looking "into" the plug hole.

  3. Rotate the engine clockwise (direction of operation) via the eccentric bolt until apex seal is positioned across the center of the #2 rotor trailing (top) plug hole.

  4. Mark the timing wheel position at the "timing pin" which sticks out from the front cover.

  5. Again rotate the engine slowly until the same apex seal is visible across the bottom sparkplug hole.

  6. Mark the timing wheel.

  7. Bisecting the arc between the two marks yield TDC (of the #1 rotor).

Funtional yet Attractive,
Carlos "Spic Racer" Iglesias
'93 RX-7 (Hibernating during a So Cal Disposable Income Winter)


From:BrunoL. Soto" (
Date: Jan 29, 2002

I read the article regarding how to find the top dead center. Well this email is to inform you that, if you follow that procedure you will never find top dead center and the reason for that is because the holes of the spark plugs at no equally distance from each other, in other words the trailing hole is something like 15 degrees btdc and the leading is something like 5 degrees atdc.

The way to find the top dead center is to move the crackshaft 90 degrees counterclockwise.

I have installed a haltech system in my car and I needed to cero the ignition, but since the pulley does not mark the 0 degrees mark, I had to find out somehow, I even tried the procedure described in your webpage, only to find out that the holes of the spark plugs are not equally distance from TDC.

since I blown my engine it was time to find out and mark my pulley at 0 degrees. Well all you have to do is to take of the pulleys from the crankshaft and then rotate the crankshaft until  the wedge is at the very top, you can use a level to make sure that the wegde is at the very top. In my case I use the flywheel, since I did not have the engine in the car. Well after you make sure that the wegde is at the very top just rotate the crankshaft 90 in this direction <=== (counter clockwise) and that is it.

When I installed the haltech system some drawings of the CAS had 2 marks (rx7-3er gen), and when I looked at mine, It just happend to had one, my question was ??? degrees that mark? well it is exactly 20 ATDC.


Editor's note: I trust Carlos' knowledge, period. But Bruno also seems to make technical sense. Maybe someone more knowledgeable than I am can shed some light on this? --Steve


Date: Sat, 3 Jun 2000 14:24:39 +0200
From: "Bernd Kluesener" (
Subject: RE: (rx7) [3] Crank angle sensor wheel notch?

> does anyone know what the timing is at the "notch" (arrow)
> on the timing wheel?  i have asked many people and no one
> seems to know.  its not in the workshop or mazda training
> manuals.  i wanted to hook the car up to an oscilliscope,
> but don't know what the timing is.  anyone got a clue?

At idle speed, i.e. below 950 rpm, that notch represents 5deg after TDC if you connect your timing light to the leading plug and 20deg after TDC if connected to the trailing plug.

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