Hi Suzi and Steve, hope Mom is OK.
You have the style U I C O 5 The I between U and C is TDC...........the O is the BALL..........the 5 signifies that the ball gives five degrees of advance timing.
Set the pointer on the BALL........you have the BALL
The better way to say it is: When you find TDC compression on no. 1, you should see the pointer near the ball. That will be close enough for now. Then observe where rotor points. Put on the dizzy cap and wire the dizzy per firing order starting at where rotor points. Most of the time the rotor is just past the correct dizzy hole because of the lag time of you stopping rotation and the advance needed.
The finishing touch is done with a timing light attached to no. 1 plug, motor running at idle, timing light flashing thru the hole in bell housing so as to see the pointer. You then turn the Dizzy until ball is right on the pointer.
This will be TMI (Too Much Info) But you seem to want to learn and that is part of what Stovebolt is.
We all are talking about TDC compression. Finding TDC compression on no. 1 cylinder. Initially you find it by feeling the actual pressure with your thumb or your favorite method. This tells you that you are not on the exhaust stroke but are actually on the compression stroke. So you stop turning the motor. Set the dizzy and plug in the wires. You won't be exactly where the motor runs the best, just close. But motor will start.
So then on these older motors, you look into the hole in the bell housing where there is a pointer and some markings on the flywheel. Hopefully still in the window. That brings us to this other TDC we keep talking about. These marks. One is actual TDC that tells you when the piston is at one of it's TDC's (exhaust or compression). But you know it's the compression one because you felt it or saw the Kleenex blow out or you are a looker at valves. Now then, here is the coupe de grass. We don't do anything with that TDC mark on the flywheel except say "hey that's cool, I think I did this kind of right!"
But we know that Chevy wants us to actually have the pointer on some other mark because we need to have the proper advance timing. What's that mean? Well, the spark causes an explosion inside the cylinder chamber. in this case, 6 explosions, one at a "time". This is what gives us the power to drive the wheels for Suzi to go shopping.
BUT!!!!!!!! when should the explosion happen? It needs to happen when the piston is on it's way down from TDC. NOT on it's way up to TDC. that would blunt the power. SO.......the engineers said hey, that piston is sure traveling fast going up and down and up and down. If we initiate the spark at TDC and the fuel ignites and blows up and the energy translates to a force on the piston top, the piston will be long gone down. We need to "time" the initiation of spark "before" that. Like "before" TDC. Like in "advance" of TDC. Just a tad. So lets try initiating spark at 5 degrees Before Top Dead Center and let's call it 5 Deg BTDC. Heck the flywheel and all that distributor stuff is all bolted or geared together. Splendid idea. So tell the owners to set the timing at 5 deg BTDC. How will they know when that is? How about a BB or a ball on the flywheel? So they can be on the ball. Get it? On the ball. Then depending on what gas they use, how old the motor is, what altitude they live in, what climate they are in and what day it is, they can tweak it till it runs good. But wait! as the piston goes faster and faster, 5 deg won't be enough advance. OK we will add variable advance with weights or vacuum. Stuff like that. Splendid idea.
Later on, GM got rid of the flywheel markings and made it a lot easier. Marks on the harmonic balancer with hash marks on either side of "ZERO" (TDC) and a pointer sticking out of the block............ or just one mark on the balancer (TDC) and a plate attached to the block with a zero and hash marks on either side.
Just in case: A timing light shows you when no.1 plug is firing. It actually is a strobe light in effect. "Freezing" the flywheel to see the marks. If the pointer is not on the ball, you rotate the dizzy until it is. Then you tighten the dizzy clamp bolt. Small adjustments to eliminate slight ping can be made using the octane selector without loosening the dizzy clamp bolt.
File it under FYI TMI FWIW
