IIA Primary Pinion Threads

[jp88]

Now this is admittedly beyond what I'd expect anyone to recall, but should you know you will rank among the gods of rover knowledge....

I'm installing a brand new, genuine IIA Primary Pinion (C suffix), but the threads definitely do not match up with my old primary pinion lock nut. The lock nut will turn 1 revolution and then come to a hard stop. When I look at the threading, the new primary pinion threading is clearly courser than the lock nut.

(And as a test, the locknut spins smoothly on the old primary pinion).

The only other difference I see between old and new primary pinions, is that the old one is a uniform shade of steel grey, while parts of the new pinion have a copper hue. Weird huh?

The parts supplier swears the pinion is genuine, and the correct series. And by way of sanity check, the constant gear, which is part of this matched set, readily slides onto the layshaft. I tend to believe these guys anyhow, they've been very upfront.

Any ideas? The parts catalog says there is only 1 primary pinion locking nut for all Series (#213416)

[antichrist]

Try an M10x1

[jp88]

Thanks Tom. I had hoped to keep the parts original. Maybe it's a necessary deviation. Appeciate the sizing info.

[antichrist]

I don't know that that's what it is, but it's possible as that is what coilers have, which have basically the same diff, just a different ratio.