A recent distributor drive gear swap got me thinking about the gear and pin. I tapped out the pin on my 394 Olds distributor to swap on the gear from my 324. The gear's pin tapped out easily, but is a solid pin that has been peened over to stay put. But in terms of replacing it, what is the best, or even acceptable, practice in replacing that pin? Some sources show that a roll pin is an acceptable replacement for the solid pin, which I think is 3/16". A quick look on McMaster would show that a basic spring steel roll pin has a breaking strength of 4,100 lbs. Is this an acceptable replacement for the solid pin? What about a cut off drill bit? It's probably better that a pin shear rather than stay together and twist up the cam and gear, right? Am I crazy and overthinking this? Would love to hear some feedback on this one.
I suspect that if a roll pin was adequate, the factory would have used one to save the few pennies...
A roll pin is fine. There is not much shear force there. Thats why Comp Cams makes composite gears. As for cost of manufacture, a roll pin costs much more to make than a solid pin.
might depend on the distributor. Some gears are pressed on and retained with a light duty roll pin, others are a slip fit, and the pin is solid and peened, some use a single layer, but substantial, roll pin. I'd use the original design, and make a new pin if needed (perhaps if you ground off a peened end)
I'd imagine that there is even less shear force on the distributor now that it has a pertronix, without the drag caused by the points.
I've seen solid pins taken out and replaced with nested roll pins....find the roll pin the OD you need, then a second small roll pin to press inside the larger roll pin to double up the wall thickness. Ends up similar in fashion to the stock Ford multi-layer wound spring steel pin.
I do not know about your Olds motor, but the SBC distributor also drives the oil pump.......considerable load0n the gear at higher RPMs.
I had a sheared distributor gear roll pin ruin my LSRU weekend one year. The pin split into three pieces, so it was not immediately apparent that the gear was freely spinning around the distributor shaft. When I put it back together, I installed an original-style roll pin back in it, and then added another smaller one inside that for good measure. Probably overkill, but I didn't want to do that job again.
For the Olds, it seems the oil pump drive is part of the gear ***embly, so the resistance caused by the oil pump drive would be transferred into the gear alone, and the roll pin would only be responsible for turning the distributor drive. As you correctly point out, that's not the case in all applications.
A roll pin and a spring / tension pin are 2 different things. A true roll pin is almost a solid pin and it is very strong.
I am always amazed at the strength of that pin in a disturber! Being a Ford man I have seen that long oil pump drive shaft twisted up like a pretzel! That always amazed me! I would figure the pin would shear before that shaft, even though small, twist like that! Always kinda worried about that pin on receiver hitches on heavy trailers too! Bones
If you have a steel gear, just tack weld it to the shaft after you put the pin in. Won’t go anywhere then.....
The stock Olds pin seems to be relatively soft, I replace with grade 5 bolt shank and peen both ends.
I have seen roll pin failures. They are too brittle, too "springy". I replace them on my race motors with a piece of tough 1/8" welding rod. I TIG a ball end on each end to prevent movement. This eliminates the problem of sheared pins, even when using an aggressive high lift roller cam and hi volume (hi drag) oil pump.
The Jalopy Journal
