Re: Resetting Timing Mark

[Simon Favre <simon@xxxxxxxxxx>]

Well, I hate to dispute a regular contributor, but these are both a bit
inaccurate. The problem with TDC is that the piston moves very little
right at the top, while the crank moves several degrees. Here are 2
variations on Robert's techniques that are considered much more accurate:

1. Set up the dial pointer as described. When you think you are at TDC,
set the dial to 0. (All good dial indicators let you rotate the bezel to
set the 0 point.) Now rotate the motor around again until the indicator
is at -0.020" and before TDC. Mark the position of the pointer on the
crank pulley (you have to put the pointer back on somewhere). Rotate the
engine until you are again at -0.020" on the dial indicator, but AFTER
TDC. Mark the crank pulley again. Bisect those 2 marks on the crank pulley
and you have true TDC. Of course, this is a lot more accurate with the
motor out and a degree wheel on the back of the motor, but this will get
you very close with the motor in the car. Once you have marked the true
TDC on the pulley, rotate the motor around again until the pointer points
at your true TDC mark. If this is not pointing at the factory mark, move
the pointer until it is, and erase all 3 temporary marks. Recheck using
the same procedure.  These are basically the instructions you would get
with a degree wheel for setting it to 0. You might have to play around
with different deflections to get the center right. Using +-0.030 should
make the readings more repeatable. The greater the difference in readings
you use, the farther apart the temporary marks will be, but they will 
also be more repeatable.

2. Lacking a dial indicator, you can make a hard stop out of an old spark
plug. Bash out all the ceramic stuff, and the ground electrode(s). Drill
and tap the shell for a long bolt. Put a bolt with a rounded tip and a
lock nut onto the plug body. Don't put it in the motor yet. Rotate the 
motor until you are a few degrees off of TDC. Screw in the hard stop and
adjust the bolt so it just contacts the piston crown. Now, this is VERY
IMPORTANT: you have just put a hard stop into the motor. DON'T ROTATE THE
MOTOR ALL THE WAY AROUND!!! GENTLY rotate the motor forward to the stop.
Mark the pulley. GENTLY rotate the motor BACKWARD to the stop. Mark the
pulley. Bisect the 2 marks as before to find true TDC. Remove the hard
stop, and rotate the motor to your new TDC mark. Reset the pointer to the
factory TDC mark. Whew! Note that since this technique involves rotating
the motor backwards, I would NOT use it on V6 engines.

Both the above techniques are old racer's tricks. My racecar has 2 degree
notches cut into the crank pulley from 34 before to 10 after TDC. That
makes setting the pointer easy. I have to use the hard stop method, as it
is not an Alfa motor with the plug directly over the piston crown. It's a
Fiat 1100 with the spark plugs coming in from the side at an angle. A dial
indicator with a deflection lever would work, but not the regular plunger.

If you want to time your car accurately, and you don't have a degree wheel,
you really should use one of the above 2 techniques.

Remember, a timing light is an instrument for illuminating grease spots
on crank pulleys. ;=)

Robert_A_Brady wrote:

>Regarding resetting the crank pully pointer:
>
>1.  If you have a dial indicator, remove the spark plugs, insert it into
>the spark plug hole for cyl.  #1, turn the engine by hand while watching
>the dial, when the dial goes to max deflection, that's top dead center.
>Reattach the pointer so it aligns with the pully mark.
>
>2.  If you don't have a dial indicator, insert a screwdriver down the
>spark plug hole.  While turning the engine, you can feel the piston
>rise, and then fall.  You will notice that the crank can be turned a bit
>when the piston is at it's top point.  Align the timing mark to the
>middle of that "dead zone."

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