Why do Valves like Marvel Mystery Oil so much?
I’m in the process of breaking-in a partially rebuilt XPAG engine. It has new pistons and rings, new stellite valves, hardened valve seats, (in fact every moving part on the head was replaced or refurbished). I’m up to 700 miles on the break-in. I’ve changed the oil several times along the way. If I don’t add some Marvel Mystery Oil to the crank case, the valves sound angry and one of the exhaust ones will stick. With the MMO, the valves sound happy and no sticking. The valve guides are cast iron (not bronze) and the head was rebuilt by a reputable professional, so it’s unlikely the clearances are out of spec (but I suppose anything is possible). In any case, why does the MMO help so much? Is it possible that the new valve stem seals are sealing too well and starving the stems for oil? I guess I’m assuming the MMO penetrates better than the regular oil, and can get past the seals. (BTW: I’ve met many ‘T series owners who absolutely swear by MMO.
