Top end break in, heat cycling

[rpduc]

Well I finally found time to get the MC back together with replated cylinder, new Vertex piston etc. She fired up on the 3rd kick. as per instructions from Millenium I just let it idle for ten minutes and shut it down.

I now will commence with the break-in procedure recommended in the owners manual unless some of you characters have a better suggestion.

I was surprised by something in the manual when looking up the recommended break-in procedure.

"Below 0º C. do NOT use 100% synthetic oil"

What is the logic there? I used Amzoil Dominator in my MC for a couple rides last winter out on the ice. -10º C. The jetting was corrected per the manual and it ran fine. When I pulled top end there was some scoring on the piston. It may have been there even from the P.O. but I'm just curious if anyone has thoughts on this synthetic oil theory.