Pretty much everyone knows not to use automotive engine oils in their bike, and most would know it’s because auto oils use friction modifiers. But why? Don’t we want to reduce friction in our engines? Yes we do. The difference between auto and bike engines is not where friction modifiers create the problem. It’s the clutch that suffers.
Friction modifiers can cause problems in motorcycle clutches and gearboxes. Consult your owners’ manual and use the oil recommended by the manufacturer.
What we’re trying to tackle here is the reasons for not using friction modifiers in four-stroke motorcycle engines. We’re not going to try and explain the chemistry of friction modifiers. If you’re thirsty for that kind of knowledge, see the propeller-head panel.