What engine, Tom?
sstock's reply is excellent, but it should be noted that the sweet spot (timing mark) is not necessarily the the same for same engine in different years.
And, the "sweet" spot is not the same every year for the same engine (at least for Stovebolt six engines: 216, 235, 261).
And, using an original flywheel for the engine might show "THE sweet spot", but you often cannot be sure that the flywheel that you have is the original flywheel that came with the engine to which it is now attached.
Is that confusing enough?
