Assuming that you just need to find close to TDC for the leak down test:
A simple way to find TDC of the compression stroke is to:
1 Remove all the plugs.
2 Put your thumb/finger over the hole for number 1 spark plug.
3 Crank engine (I use one of the hand held switches, but you
could have some one "bump" the starter with the key)
4 When you feel pressure under your thumb/finger, the piston is
coming up on the compression stroke.
5 Use the timing marks to finish bringing it up to TDC (assuming
that you have timing marks that show TDC). I.E. rotate the engine
with the starter, wrench, or as others have suggested, by rolling the
car in gear.
6 Repeat for the other cylinders.
On four or eight cylinder cars, you can make a mark on the crank pulley/damper
to indicate 180 and/or 90 degree increments. On 6 cylinder cars, you will have
to mark every 120 degrees (or something else if you have an odd firing V6).
I use some old, un-used nail polish - white or red - to make the marks. The
polish dries quickly, and usually lasts. Note: Do not use your
nail polish without permission!! 8-)
I doubt that you have to bee that accurate to do a leak down test, just pretty
close. The degree wheel is always useful, but it may not be necessary for the
test, and they can be a hassle to install/use while the engine is in the car
the radiator/fan(s) are in the way. I assume that you just want the piston
TDC to minimize the volume in the chamber...