Here's a quote from a motorcycle message board I'm a member of. What do you think of this line of reasoning regarding automotive oil in a motorcyle?
"Depending on the bike, some have different bearings than cars (i.e. plain bearings vs. roller bearings). Oil for cars is designed to work with plain bearings, which have no moving parts. Some motorcycles have roller bearings, and using car oil will cause roller/ball bearings to slip/skid/hydroplane. Over time this will cause a flat spot on the roller or ball...and eventually...boom. When a bearing lets go, all **** breaks loose. Safe bet to stick with oil designed for your bike."
"Depending on the bike, some have different bearings than cars (i.e. plain bearings vs. roller bearings). Oil for cars is designed to work with plain bearings, which have no moving parts. Some motorcycles have roller bearings, and using car oil will cause roller/ball bearings to slip/skid/hydroplane. Over time this will cause a flat spot on the roller or ball...and eventually...boom. When a bearing lets go, all **** breaks loose. Safe bet to stick with oil designed for your bike."