Crankcase mating surface shiny or dull?
 

I am rebuilding my 2.7 mag motor.
The old casing sealant has been removed but the mating surface is a dull grey however I can scrub it back to shiny. Is this necessary for a good seal? I don't want to damage it if I can leave as is.
Cheers!

The answer is - no. As new they came with a zinc dichromate coating, which is a sort of dull gray. Aggressive cleaning will remove it and the surface will then appear shinier. It is not uncommon to see both on a case mating surface, patches of gray, and also shinier areas.

Great thanks. I shall make sure they are cleaned and degreased and not go too crazy trying to get them shiny.

Do clean thoroughly of course, but I've never heard anyone say shiny or dull is preferable for a proper seal.

Ensure the surfaces are flat....

As you are rebuilding a Mag case motor, I trust all appropriate machine work had been done? Align bore check/machining, case mating surfaces trued, case savers/timeserts installed, maybe dowel pins, spigot bores trued etc??

If not, don't worry too much about which surface finish is appropriate for the mating surfaces....

Cheers