Reply to "Double pinning distributor gear?"

On the subject of distributor gear pins; I recently had a discussion with an engineer at Spirol, who make slotted roll pins. As per conventional 351C engine building wisdom, he confirmed that double pinning a 1/8" carbon or chrome stainless steel roll pin (with a 3/32" roll pin), increases its double shear strength from 1,875 lbs to 3,025 lbs. Some have mentioned increasing the size of the hole and going up to a 5/32" roll pin; however, that's not quite as strong (double shear strength of 2,750 lbs). It is possible to double pin a 5/32" roll pin (also with a 3/32" roll pin), which gives a double shear strength of 3,900 lbs, but you need to drill a smaller hole than you would if you were using a 5/32" pin on its own. You only benefit from the inner pin if it fits tightly into the ID of the outer pin.

As an aside; Chevy's use a 3/16" roll pin, which has a double shear strength of 4,150 lbs. Unfortunately, it's not a good idea to drill a 3/16" hole in your 351C oil pump drive shaft because the diameter of the shaft isn't sufficient.