I have just rebuilt my 51 Mercury flathead and am getting ready to start the breakin. Anyone got specific ideas about oils for the breakin period to help better seat the rings? In aviation, we normally use straight mineral oil for the breakin period and then switch to the standard type. With a honed cylinder and new rings, is there an optimal proceedure to use to give the best seating of the rings? Also, when broken in, what is recommended for the standard oil to use for day to day use. I've heard that adding Zn to the oil is a good idea, but is there any recommendation for a specific brand/type to use or just any good 10W-40 or so? Thanks, phil w.

 

what i understand you are only suposed to use 30w non detergent
that is all i use in my 48 it seems to like it

 

If it were me I would use 10/30 Valvoline VR-1 racing oil for breakin. It already has the ZDDP. Then after 500 miles or so switch to 10/40 or 15/40. Every other oil change put in a can of ZDDP additive, like comp cams or other brands. For each respondent here you will probably get a different answer, but good luck and congratulations on your new flathead!

 

Thanks for the information, y-block. It's interesting that with so many engines out there, that there isn't more information available for the break-in period. Your ideas sound good. If I could just figure out the rest of the wiring, I'll be ready to get her cranked. Appreciate the help. phil.