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Veteran Contributor
Posts: 75
Registered: ‎05-17-2010

Re: Can you mix 85w 140 and 90w 140 in final drive?

Traditionally gear lubes have always used sulfur to add shear properties.  That's why they stink.  Modern engine oils have very little zinc these days, which also provided shear properties. 

That is one reason why modern engines all use roller tappets to eliminate the shearing action of the cam lobe on the lifter.  In my old double overhead cam motorcycles I use engine oils

meant for older diesel tractors, which (at least used to) has higher levels of zinc or other shear additives.  Those old bikes have super stiff valve springs and plenty of shearing action

between the cam and lifter.  Haven't had any any problems yet.