Motorcycle Oil VS. Automotive oil - Colorado Sportbike Club Forums

Re: Motorcycle Oil VS. Automotive oil

One thing to think about:

When the API specification for new car oils moved from SG to SH (and beyond), the amount of zinc diphosphate in the additive package dropped dramatically. Zinc acts in oils as an extreme pressure lubricant, helping to prevent galling/metal to metal contact on parts that do not receive direct pressure oiling (flat tappets in car engines, transmission gears in motorcycles, for instance). The zinc had to go because of federal mandates concerning the warranty on emissions controls, particularly rhodium/palladium catalysts, which are poisoned by zinc.

Use of car oils carrying the SH or later API spec can not only cause the aforementioned clutch issues, but in engines that are heavily loaded, can cause galling and pitting of transmission gears and shift forks.

Diesel oils still have sufficient amounts of zinc to provide adequate protection for the transmission, but may not have the correct chemistry to resist shearing at higher RPM.

Full synthetics are definitely the most effective lubricants, but may have some disadvantages in term of leakage and oil consumption, particularly in engines that are older or have very high mileage.

Ok...so that was more than one thing...

Source: http://www.cosportbikeclub.org/forums/showthread.php?t=44588

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