Dead Reckoning

[Tom Kysilko]

At 07:06 PM 7/25/2001 -0700, A. Maberry wrote:
>Used in timing automobile engines. The timing is determined by the
>uppermost travel (top dead center) of the number one piston (which equals
>the point of maximum compression in the number one cylinder. It's
>certainly been a long time since I tried to tune my own car, so
>someone please correct me if I am mistaken.

Allen is correct about the involvement of the number one piston, but I
think that the practical use of TDC is in reference to the position of a
"timing mark" on a pully, gear, or flywheel connected to the crankshaft at
the moment that spark plug fires.  TDC and BDC are indeed 12:00 and 6:00.

Brings to mind my favorite (if not necessarily most accurate) movie accent
-- that of Marisa Tomei in "My Cousin Vinnie" in which she announces that
the timing of the '64 Chevy 327 is set to "foah degrees befoah top dead
cennah."

  Tom Kysilko        Practical Data Services
  pds at visi.com       Saint Paul MN USA