This is the stock connector...
This is the stock connector for an MSD ignition between the distributor and the 6AL box. Notice that the black-and-purple wire connects to the green wire and not the purple (technically “violet”) wire as you might expect. This isn’t a problem if you never change the connectors as they won’t allow you to plug them together backwards, but if you swap these connectors for Weather Packs make sure that you get this right. Reversing the wires will advance your timing up to 30 degrees or more, causing detonation.
There are two easy ways to make sure the cylinder you are checking is on the compression stroke. You can pull the valve cover and see if you can wiggle both the intake and exhaust rocker arms. This means there is no pressure on the rocker arms and the valves are closed. An even easier method is to pull the spark plug for that cylinder and plug the hole with your finger. Don't stick your finger all the way into the combustion chamber, especially if you are bumping the starter to turn the engine over! As you turn over the engine and the piston comes up, you should be able to feel pressure building against your finger.
Once you know you're on the compression stroke, remember to set the timing mark where you want the plug to fire, not at cylinder TDC. Check your timing with the pointer against the timing scale on the harmonic balancer. It only needs to be close right now; you can fine-tune it with the timing light later.
Next, you're ready to prime the oil pump. There are special shafts available that allow you to spin up the oil pump with an electric drill. Remember, Fords and Chevys spin the distributor in opposite directions. If you're priming a Ford motor the drill needs to spin counter-clockwise. On a Chevy it needs to spin clockwise. Don't depend on the assembly lube your engine builder used to protect the bearings and valvetrain on initial start-up. If you don't prime the oiling system, it can take several seconds or sometimes up to a minute for the oil pump to fully pressurize the engine all the way up to the cylinder heads. In that time a lot of damage can be done. Spin the pump until the oil pressure gauge begins registering pressure and then keep going for five full minutes. It may seem like a long time but this is one of those cases when it definitely is better to be safe than sorry.
A rookie mistake when cranking...
A rookie mistake when cranking the engine for the first time is to mistakenly set the ignition to fire at TDC, or zero degrees advance. Instead, set your timing pointer for the amount of advance you expect the engine to run (30 is usually a good safe number if you are looking for a starting point) and then install your distributor.
Now you're ready to install the distributor. Grease the gear with a high-pressure lubricant or lithium grease. Install the distributor in place with the rotor pointed in the spot you want the No. 1 terminal to be (generally, that's as close as you can get it to the plug). Now, install the cap and wires, and remember which terminal the rotor is pointing to. Know your firing order; the distributor fires sequentially (counter-clockwise for Ford, clockwise for Chevy) but you have to know in what order the cylinders fire. With that done, you are ready to fire the engine.
If the engine is running smoothly, that's a good sign you have all the plugs firing in the correct order and you can move on to fine-tuning the timing. Plug in your timing light and make sure it's connected to the No. 1 plug wire. By shining the light on the timing pointer and reading the scale on the side of the harmonic balancer, you can tell exactly where your timing is. Advance or retard the timing by turning the distributor housing. Once you have it where you want it, tighten down the hold-down clip. If you're running an advance mechanism, make sure you check the timing with the engine rpm at a level where the timing is fully advanced.
Now you're set. If your engine is on a dyno, you can make several pulls with different amounts of timing to determine what your engine likes best. If the engine is already in your race car, you can do the same thing at the track with your stopwatch. Just remember not to advance the timing so much that the engine starts detonating.