Your experience and motorcycle engine, as well as condition and upkeep maybe different from others.
And, it is perfectly ok to have a different point of view from others on this forum, as well as life in general.
In the end, it IS Your money, so Your choice
Please see the below results from our mutual friend, Google as well:
Automotive oil is formulated as a engine crankcase oil - motorcycle oil is formulated for 3 jobs, a crankcase oil, a transmission-gear oil, and a wet clutch oil.
The most important difference is the wet clutch oil, automotive oil won't work cause of the energy saving formulation will cause a wet
clutch to slip. The average motorcycle engine is a high performance engine, pumping out 4 times more horsepower compared to the bigger size of an automotive engine and the correct formulation of motorcycle oil is important, this oil works harder and more and more is expected from motorcycle oil - that's why it usually costs more per liter as well.
To some people, changing the oil in your car is just like changing the oil in your motorcycle. Just drain out the old oil, and pour in the desired amount of new oil and you're done. So when it comes time to change your motorcycle oil, why can't you use the same oil that you use in your car? Motorcycle oil and automotive oil look and feel the same so how could there be a difference between the two?
Automotive oil looks pretty enticing at lower price per quart/liter but any experienced motorcycle rider knows that using automotive oil in motorcycles causes serious damage. In automotive vehicles, the engine is always separate from the clutch and transmission so they have separate oils for each.
In automotive engine oil, there is more of what is called "friction modifiers" to help lessen the amount of friction on engine components and improve fuel economy. Of course, improving fuel economy has always been the main goal of the automotive industry; therefore, making friction modifiers a necessity for all automotive oils.
These friction modifiers that are added to automotive oils are what cause serious damages when used in motorcycles. The friction modifiers clog the clutch plates in a motorcycle's transmission causing serious clutch slippage and disabling the motorcycle. Motorcycles have to be as compact as possible and to do this, the engine and transmission have to be combined together into one casing. This means that everything is lubricated by only one type of oil including the valves, piston, transmission, and clutch.
Motorcycles require very little and/or no friction modifiers to help improve clutch friction and to prevent clutch slippage. But to make up
for this lack of friction modifiers, motorcycle oils use higher levels of anti-wear additives such as ZDDP, also known as phosphorous, to
limit engine friction and wear. So, motorcycle oil has extra anti-wear additives and is lubricating so much more than automotive oil.
To some people, both oils look and feel the same but now you know the facts of each. So the next time that you decide to change your
motorcycle oil, go straight to your local motorcycle dealer and buy only high quality motorcycle oil designed specifically for the type of
motorcycle you own. Make sure that you change your oil periodically to keep it fresh and clean to ensure a long life for your engine,
transmission, and clutch.
Car gearbox oil only has to do one job, bike engine oil has to do two jobs, lubricate the engine AND gearbox, which is a very different thing indeed.
I'm sorry but removing the clutch plates and 'scuffing them up' will not undo any problems, the friction material will be contaminated by the car oil and they will most likely need replacing, any slipping will also ruin the steel plates by overheating them, causing them to warp and blue.
I have run 10/40 semi synth in a few bikes when I was skint, but not anything with slippy additives, without any major issues, I tended to change it more often too which probably negated any cost savings.
Motorcycle oil doesn't break down as fast as automobile oil...... There's a reason it's not all sold as the same! Very true...
All oils are not alike, even Motorcycle oils.
Some M/C oils, such as AMSOIL, have specific anti-wear additives designed for the transmission and anti-rust and corrosion inhibitors for periods of non-use.
Generally bike oils have more EPA's (extreme pressure additives - deals with 'metal-on-metal' contact in the gearbox) and different molecular chains (again 'cause of the gearbox). The molecular chains are what gives it the ability to change viscosity, and the gearbox can mess with 'em.
Car gearboxes use separate gear oil, whereas bike ones use engine oil.