first evry thing I have read or herd of about split wt oil is the first #is the wt.the secend#is the viscosady being the same as say a 20/40..is a 20wt.oil but has the same vis.as 40wt.well I think the older motor dont like the split wt.evry oil motor I have put it in will smoke valves will tap and will use oil..go back to a strait wt. and evry thing is fine..im not an expert but I have biult to meany motors to count most of them are still out there raceing and being driven daly with no trouble and they all run strait wt oil..thanks Artie
