Distributor drive gear pin

[Nick Salmon]

Advice please... Is it OK to use a suitable size roll pin instead of the usual mills pin to secure the distributor drive gear?

[Ruairidh Dunford]

In my experience, yes, entirely suitable.

[Tony Griffiths]

The size is, I believe 1/8". I've a box of assorted sizes so I checked a sample batch of 1/8" and they measured, variously (across the diameter with the slot upright) as 0.1310", 0.1315", 0.1320" and 0.1335".

[JonE]

is there thus any special requirement for how one inserts a roll pin? - do they just go in a little bit and then compress in a vice with some blocks?

[Nick Salmon]

Thanks Ruairidh.

[Tony Griffiths]

is there thus any special requirement for how one inserts a roll pin? - do they just go in a little bit and then compress in a vice with some blocks?

"Spring pins have a body diameter larger than the diameter of the hole they are intended for and a chamfer on either one or both ends to facilitate starting the pin into the hole."
Once started, they can be driven in with a hammer - or similar - the spring action of the pin allows it to compress to assume a tight fit in the hole.
It helps to grind a shallow taper to help get them started.
If you find an original fitting, the parallel pin is domed at each end - presumably some sort of assembly jig being used to close the ends down simultaneously.
Note though what I discovered about the variation in quality control of these items: for a 1/8" hole a selection was measured, variously (across the diameter with the slot upright) as 0.1310", 0.1315", 0.1320" and 0.1335". All greater than 1/8" (0.125") and no doubt all useable.

[A G Wood]

To further endorse Ruairidh's  recommendation, a lot of later vehicles (those that still use distributors, that is!) use roll pins for just this purpose.

The usual workshop manual advice is to fit these pins such that the direction of (shear) force applied to it is such that the pin isn't constantly being 'squeezed' open & closed. Thus, for the distributor application the split in the pin is on the axis of the drive gear  rotation ("E-W"), and not on the longitudinal axis ("N-S")  of the shaft, and for (say) a gear shift fork application the split in the pin is on line with the shift rail. Having said all that, I've often seen them fitted incorrectly in both applications seemingly without ill effect.

The pins are nominally sized, so that a 1/8 pin is supposedly suitable for use in a 1/8 hole, but the manufacturers seemingly have different ideas about the amount of allowable compression of their own pins, so the unfitted ODs will vary. And you may have to put your own chamfer on them to ease fitting.
 RuairidhRuard Ruairidh