Why do we set the #1 TDC at 5 o'clock on the distributor?

As I was putting my F head back together, I installed the new oil pump and clocked the distributor so the #1 cylinder TDC points at 5 o'clock on the distributor rotor. It got me thinking, why 5 o'clock? It seems to me that it wouldn't matter where the #1 TDC was pointing as long as you install the spark plug wires correctly. I'm just curious. Every manual says to make sure #1 is pointing at 5 o'clock.

 

Other than the old air cooled VW engines, which has a couple degrees retard built in for cyl 3, I have never seen an engine where it is critical to have a specific location for the #one cyl location. Just drop in the distributor, determine where the rotor is pointing when #1 TDC, and wire it up in the firing order.

If you dont know the firing order, you can feel for the compression at each spark plug hole, and set the wires that way-----BTDT.

 

I did it correctly, don't get me wrong. I was just curious why 5 o'clock. I mean, why not 2 o'clock or 7 o'clock, etc. The reason I was curious was because the reproduction distributor I purchased is keyed backward from the original one I have. The first time I built the engine, I clocked it for the the original and then replaced it, which then put #1 TDC at 11 o'clock and it worked just fine. Now that I had to rebuild it with a new oil pump, I clocked it for the repop distributor so it is back at 5 the way it should be. Again, just a curiosity.

 

The exact position can readily effect the ability to properly advance the distributor.

Note: the 5 o'clock position is not correct for any CJ-5 with the original factory distributor.
See: http://www.film.queensu.ca/CJ3B/Tech/DistributorInstall.html

 

Thanks, Oldtime. That article explained a lot. Too bad I didn't read that before I installed my oil pump, I have mine clocked at 5 o'clock.