Interpretation of the Spitfire's Timing Marks


by Victor Michael

                       v~~~ timing mark @ 10 deg BTDC
----------------------::-------------
====== <--- spin  ==================<  crank pully
----------------------::-------------
 16 12 8  4   .   4  8  12 16 20 24
 .  .  .  .  /|\  .  .  .  .  .  .
/|\/|\/|\/|\/ | \/|\/|\/|\/|\/|\/|\
              |
   ATDC      TDC      BTDC

TDC  = Top Dead Center (piston in cylinder is straight up at ignition)
BTDC = Before Top Dead Center (advance; ignites when piston on way up)
ATDC = After Top Dead Center (retard; ignites when piston on way down)
* Each tooth point is 4 degrees, so each mark would be 2 degrees.
* The timing mark represents the piston and spark for cylinder 1.
* The specs in the books and stickers call for timing at 10 deg BTDC.

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