[Mogger]

but I seem to recall that one was not supposed to use synthetic on a new engine - in order to allow the rings to seat.

This was true 40 years or so ago, depending on what rings you happened to get in an engine.

Around 40-50 years ago, Sealed Power Corporation developed pre-lapped, radiused rings.

It took several years to license most or all of the other ring manufacturers to make them.

Since that era, to the best of my knowledge, no break in is required as all new engines should have rings made that way.

Working in a machine shop though, you might encounter straight edged rings that would require break in to seat.

Amsoil has a break in oil just for this: Amsoil Break in oil

[spankalib]

Thanks FRiend! The machine shop was 40+ years ago ;)