It's very easy to misread the timing marks. First, lets cover what's up here... On the crank pulley, there's a mark corresponding between #1 cylinder 0 degrees, top dead center (0TDC) and a timing indicator with hash marks on it in degree increments to the upper left of the pulley. The idea is when the car is idling, the timing light (a triggered strobe) will flash 'freeze' (persistance of vision) the timing mark on the pulley as is spins passed the indicator marks. It's very easy to check the timing like this. The factory service manual calls for 15 +/- 2 degrees BTDC (before TDC) for '90-'95 and 10 +/- 2 degrees for '96+.
Specifically for the Z, a timing light with an inductive sensor is needed, since there really aren't any sparkplug wires to work with. Simply put the + & - connections directly to the battery, then clip the inductive sensor to the black looped wire coming out of the power transistor on the front of the engine. This loop is powered during #1's 'spark'.. so it can be used to time the car easily.
Here's the difficult part. Now the OEM pulley comes very close to the timing indicator, so pretty much any angle it's looked at will reveal basically the same indication. The under drive pulley is a different story:
(there's no scale to things, the pic is for demonstration)
The red arrow shows the proper way to look at the pulley to read the indicator. A direct line to the center of the crank. The yellow lines show how 'parallax' comes into play. The UD pulley is smaller diameter, so there's a bit of space between the indicator & the mark on the pulley. This is where parallax can show the wrong reading. The yellow arrow pointing straight down on the timing indicator on a UD pulley would appear timed correctly, when it's actually WAY advanced. Possibly causing detonation. The angled yellow arrow would make the pulley appear to be timed a little retarded, while it's really right on. Note how both of the yellow lines might make a degree's worth of difference between the 3 line of sight angles, where the difference is enormous on the UD pulley.
Now, it should be appearant why the timing marks can seem to 'drift' on the UD pulleys. The only real way to make sure the UD pulley's marks are correct, is to directly compare the OEM pulley to the UD pulley, checking the location of the mark between the two in relation to the woodruff key slot in the center hole of the each pulley. The key 'times' the pulley to the crank, so it's crank alignment is constant inbetween the two.
Dallas DamonZ
