No announcement yet.

Finding top dead center

  • Filter
  • Time
  • Show
Clear All
new posts

  • #16
    Howdy chaps,

    The head/cylinder configuration on a 38 later Four bears no resemblance to HD/Indian flat heads of the era. If you view image #4 on row 5 at my site below the spark plug hole is at the top of these heads positioned upright behind the intake valves. That spark plug hole is a very narrow aperture at the end of a tube below the spark plug (likely to subdue flame propagation?) The intake valves are directly over the exhaust valves. Looking at image #3 you will note how offset all of this is rendering a probe useless.

    Unless you have a through-the-timing-cover oil filter arrangement it takes minutes to loosen the oil gauge and remove the timing cover. As you can see in image #2, #1 rod is right there and with the front valve adjuster cover off you can quickly determine TDC. These motors are in an extremely soft state of tune (for a reason). Though an advance setting for these is published, most just use TDC on full retard. Especially with electronic ignition I am not comfortable going with that format, rather merely using it for a baseline, focusing more on the full advance setting at highway speed which is more critical for those motors prone to run hot anyway, retarded ignition just adding to the challenge of heat rejection.
    1950 Vincent - A Red Rapide Experience