I have been down this way a while ago. The recent experience is trying. The distributor drive shaft is 1/2" ID. The drive gear boss (where the pin is installed) is 3/4" ID Original equipment was a split ( slotted) spring pin 1/8" x 3/4" worked with original
oil pump and usually warm
oil. It's the drag of the Melling high volume
oil pump with cool oil that did my original split spring roll pin in. I had great luck ( longevity) with the spiral coiled roll pin I installed 15 years ago.
I thought I had a problem but the spiral coiled roll pin wasn't the problem.. The distributor drive gear has 15 teeth. An odd number of teeth one pin hole. Installing the gear 180° out on the shaft, isn't the same. My mistake 15 years ago. It was a problem, My Mallory distributor has a mechanical tack drive and doesn't allow much movement of the distributor housing for timing adjustment. So I moved wires around the cap and reset the distributor drive gear teeth and cam teeth to get things back in to timing. 15 teeth = 24° per tooth each spark plug wire terminal is 45°. I didn't know what to look for when I tried to reinstall the drive gear on the shaft. Recently I suspected the drive gear pin had failed. I didn't know But the new spiral coiled roll pin didn't break. Back fifteen years ago, I used a longer spiral coiled roll pin. The pin had beveled ends that tried to align the gear and shaft holes some as it went in. The pin was longer than the drive gear boss was wide, so I cut the excess pin off . That was a mistake. A little pin sticking out, what would it hit? But my cutting that excess pin off turned that pin in to a one time use. Square pin ends don't help align or fit anything. I mushroomed the pin making it junk.
What was I to look for as indicator for returning the drive gear to original placement ? I now want a source and number for purchasing new spiral coiled roll pin (s) not just one . I tried a quantity to buy a quantity what I thought was spiral coiled roll pins only to ended up with DOORMAN 623-046, which are slotted spring roll pins 1/8" x !' I swear 15 years ago the spiral coiled roll pin, I bought, were from MSD and came two to a package at Local auto parts store. Again 1/8" diameter x 1 inch long spiral coiled roll pin. would be great. I'll buy a quantity this time.