I've never had a good look inside the timing cover of a marine engine,
so I don't know how the cam drives the auxiliary pump.

ALL the automotive B20s and B30s I have seen have a section in front
of the front bearing journal that is 1 3/16" in diameter and an inch long,
and in front of that is a 1"-12 UNF threaded section 5/8" long.
I suspect that the timing gear is just a hair thicker than the 1" section
is long so that the nut will put that section under tension to make sure
that it is tight.

IPD has issued repeated warnings against using an impact wrench to tighten
the 1"-12 nut (with 1 7/16" external hex) with the rationale that you are
likely to wring the nose off the cam. It may be that is what has happened
to yours and the timing gear is mounted with a Loctite product rather than
a nut. Normally the fit between the gear and the cam is loose enough that
it would otherwise come off in service, although the only axial stress is
induced by the oil pump/distributor drive gear and unless one of the two
locks up for some reason, the stress is pretty low.

If the end of the cam is off, you should be able to see a 1 3/16" circle
which would be the interface between the gear hub and the cam, and maybe
a fracture surface a little less than 1" in diameter in the center of that.

I agree with the others; I'd really like to see a picture of what you
have in there. It doesn't sound like anything I've ever seen in over
35 years of driving and working on Volvos.
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma