<VV> Using compression gauge to locate TDC ?

[Craig Nicol]

Charles wrote:
I just tried (again) to locate the correct TDC, and I used my
compression gauge (actually borrowed from AutoZone, no charge) to locate
TDC.
 
I noticed that compression spikes each time the rotor passes #1, hitting
about 50-60 lbs one time, and then 110-120 lbs the next time,
alternating between the readings.  (I removed the valve so it does not
hold the reading, as I watch the gauge)
 
I'm assuming that the low reading is the exhaust stroke, and the high
reading is compression ?
 
This is a method I had not heard before, and I'm wondering if it's valid

Craig replies:
It's a valid method. You said the gauge goes up each time the rotor passes
#1. This is natural as each time it passes #1 it's at the top of the
compression stroke. 

Normally if you installing a distributor, you would have no idea where #1 is
supposed to be (on the distributor), all you have to go by is the rotation
of the crankshaft. (CCW, by the way). One of the times the timing mark goes
past "0" you will see the gauge installed to the #1 plug hole jump and
that's the compression stroke. If there's any gauge action a full 360 degree
turn later when the mark goes past "0" a second time, it won't be much and
is a function of lifters that aren't pumped up. Ignore that one.
Craig Nicol