The Morgan handbook only recommends synthetic oil for “unusually hot conditions”.
The S&S recommendation is to use (Mobil 1) V-Twin 20w-50 Synthetic oil above 35F ambient temperature. I would tend to go with what S&S recommend for their engine. I have heard some others, who should know what they are talking about, suggest different oils but without any documented back up....... I still think the problem relates to oil pump tolerances but happy to be proven wrong.
