The Classic Cadillac Forum Discussion, Harmonic Balancer check in Past Cadillac Vehicle Discussion; So, I ordered a piston stop to test top-dead center on piston 1. Despite the vehicle chooser, the tool didn't ...
So, I ordered a piston stop to test top-dead center on piston 1. Despite the vehicle chooser, the tool didn't actually fit my car. So I made my own.
The point of this exercise was to confirm/deny the accuracy of the timing mark on the balancer. Turned out to be off by about 2.5 degrees.
In the photo, there are three Blue RTV marks. The left/right are the stop positions when the engine was rotated clockwise and counter-clockwise. The mark in the middle is top-dead center.
Thought someone may find this useful. Until I saw this done by someone, it never even occurred to me that the mark could be off. I found a guy who worked on a car that turned out to be off by 28 degrees.
While setting the timing, I noticed something. The timing mark "jumps" around about 2 - 3 degrees while the engine is running. This, plus the fact that the marks on the harmonic balancer are off 2.5 degrees, plus the mileage of the car, plus the educated guess that no one has changed the timing chain/gears ever...leads me to beleive that I will be changing my timing chaing/gears in the near future. And, of course, this means I'll be doing several other things since I basically have to take the entire front of the engine apart. This always inevitably leads to, "Well, while I'm in there..."
it can also jump around if the distributor driven gear is worn out (too much gear clearance)
The distributor, itself, is brand new. However, I can't speak for the mating gear. I'll have to inspect it when I get the front cover off. The old distributor gear showed some wear, but nothing alarming.