At 01:22 AM 9/12/97 -0400, Bob Coviello wrote:
>You can pretty well nail TDC by the method you mention (ie. rotating the
>engine while holding a screw driver in the spark plug hole to find the
>highest point of the piston's travel).
>
>A better way is to make a fixture that projects a set amount into the
>cylinder and that is immovable so that when contacted by the piston it will
>not move. Intall the fixture in cylinder #1. Rotate the crank pulley in one
>direction GENTLY until it stops when the piston encounters the fixture.
>Make a mark on the crank pulley opposite the timing pointer. Rotate the
>crankshaft in the opposite direction until the piston again encounters the
>fixture and stops. Make another mark on the pulley opposite the pointer.
>TDC is exactly halfway between the two marks that you have made; measure
>and file a permanent mark in the pulley.
>
>This second way is more complicated but much more accurate than the way
>described in the first paragraph because the arc of the piston is most
>ambiguous at TDC (ie. the piston moves the least per degree of crankshaft
>rotation at TDC), but most definate at mid stroke (most movement per degree
>of crankshaft rotation).
>
>Bob Coviello
>'80 4/4
>
Thanks very much to all of you for your encouragement and good suggestions.
I think Bob Coviello's suggestion is without doubt the most accurate one
short of dismantling the engine, or pulling the crank pulley apart and
reinstalling it. I like the language he uses, too. "...because the arc of
the piston is most ambiguous at TDC." That is an elegant way of stating the
difficulty of getting a good TDC measurement at the extreme limit of piston
travel.
Now, i just have to line up a willing and patient helper. Hmmm. maybe my 17
y.o. daughter, who's just itching to learn to drive a standard transmission...
Jerry Murphy
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