Do I need to use JASO certified "motorcycle" engine oil in my bike?

[_JOE_]

Some people claim certain synthetic oils cause clutch slippage.

I would recommend saving the 5w40 for colder temps.

Whatever oil you use, make sure you change it often!

 

[Phoenix886]

that was a great breakdown... thanks!!

 

[Thor_R]

Very good reading for an engine oil geek like me. I like the points you are making and they are very true but allow me add a few notes. First, let's sum up:

You don't buy JASO specified oil for the sake of your engine but for the sake of your wet clutch.

A high quality car engine oil will generally also work very well for the engine on your bike and it is absolutely correct that e.g. API SM is a much stricter specification than JASO in this regard. The only problem is that your clutch might not like the friction modifiers (e.g. molybdenum) used in some car engine oils and it is usually very difficult to find detailed information about the additives used in the oil you are buying. So, if you want to be sure that your clutch works and lasts as long as it is supposed to JASO-MA specified oil is so far your only guarantee for that. Some car engine oils will work fine with your clutch but it's difficult to predict whether a specific car engine oil will cause problems or not. We agree on this I just wanted to emphasize it a bit more.

There is also one reason why specially formulated motorcycle oil sometimes actually can provide better protection for your engine. This has to do with the fact car engine oils are usually formulated with catalytic converters in mind which calls for reduced levels of some additives. E.g. phosphorus is an additive which can provide extra wear protection for the engine but will reduce the life span of catalytic converters on modern cars. Still very few motorbikes have catalytic converters which means that oils formulated for motorcycles often have a stronger additive package in terms of wear protection than car oils. However, getting behind the marketing hype and finding out how much truth there is to this can also be difficult and in any case it is only logical to assume that a car engine oil which has passed a strict test for wear protection (like API SM) will also protect the engine on your motorbike equally well (but not necessarily your clutch).

 

[_JOE_]

I've NEVER heard of anyone having clutch issues with a modern, non-energy conserving oil. Can anyone give some examples of oils that effect clutch performance?