Distributors wear, so that a point gap needs to be specified in terms of
dwell angle, which for a 4 cylinder engine should be as great as possible
between 57-63°. Sometimes the point cam is worn to the point that if you
approach 63° the points won't break at all and you get no spark.

My view of timing is that it should be as much advance as you can stand
without EXCESSIVE pinging. This is usually around 22° or so. For unknown
(to me, at least) Volvo engines seem to need more advance than most other
similar engines (MG, Austin Healey, etc). A little pinging under very heavy
loads usually isn't a problem but it should not ping much of the time.
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma