During my riding club’s meet for a weekend’s long ride, one guy, who was inspired by a hack mechanic who uses imperial spanners on metric bolts and nuts, had replaced his bike’s engine oil with automobile (car) engine oil. His conclusion was, “Damn, it’s great oil! My engine is so smooth and quiet now! Highly recommended!”
I was alarmed at such a revelation.
A clutch works by forcing surfaces together to produce friction and this friction is what allows power transfer from the engine to the gearbox.
A car’s clutch and transmission are separated from the engine hence dry, which allows engine oil makers to infuse their products with friction modifiers. These compounds added to the base stock are intended to make the oil shear resistant.
On the other hand, motorcycles engines (except for those with dry clutches) share their engine oil with the transmission and “wet clutch”. Thus since the clutch plates need to grip each other while bathed in oil, the oil needs to shear just enough for the clutch – the JASO MA or MA2 rating - which is absent from automobile oils.
In other words, using automobile oil in a motorcycle engine is bad news. REALLY bad news. They may as well use shortening from McDonald’s.
The helpful person in me spoke up against this blatant misinformation and misuse. But I was promptly ganged up against, accused of being “paid by advertisers”. Another said, “all oils are the same”. But there was no topping this level of stupid: “Needing to use motorcycle specific oils for motorcycles is an Illuminati conspiracy, that’s why they are more expensive”. They then made a pact to change the oil at that “recommended” garage together. I shut the hell up and made peace with myself.
At our meet the following week, all those who had used the car oil showed up in their cars. They sat far away from me, keen to avoid eye contact. I immediately suspected what was wrong. I decided to poke the the hornet’s nest anyway, “Where are your bikes?”
Mr. Suggestion seemed to have something important in his newsfeed. Mr. Wikipedia and Mr. Oil Man suddenly found interest in a soccer game between Bhutan and Cambodia. Mr. Conspiracy was busy sipping his cranberry juice.
Finally, one guy texted me when I got home, “We burned our bikes’ clutches. Some of us found it difficult and couldn’t even shift the gears,” ending with a sad face emoticon.
So why did their engines feel smoother initially? The clutch plates were slipping against each other. Ultimately, all that slippage caused them to overheat and wear smooth.
The Takeaways:
A) Never, ever use car engine oil in your bike
B) No point talking to people who don’t listen
C) I’ve since dropped out of this “club”