[subramanyam84]

Hero Impulse had a balancer shaft. Probably the only air cooled from the Honda family in India, to have one. 8000 RPM didn't feel so unless you looked at the Tacho.

[Rocketscience]

Found this old thread while myself searching for this topic online, would have loved to have an exhaustive list of the same but manufacturers don't find this feature to be cool enough to advertise.

Anyways, what my newfound engine knowledge tells me thanks to d4a youtube channel is that balancer shaft is only one half of engine vibration story, a balancer shaft helps reduce the primary vibrations of the engines but what they fail is at cancelling out the secondary vibrations and a great deal of engineering is needed to truly smoothen out vibrations out of an engine. (And not just simply adding a balancer shaft)

The R15v2 for sure comes with a balancer shaft, again thanks to youtuber Jeet Bhaskar for dismantling the engine in detail, one can assume that v1 would have it too since they both had pretty much an identical engine and v3/v4 should have it too since they are derivatives of that same engine.

Also, despite the balancer shaft i don't find my R15v3's engine to be that smooth or vibration free (It is average at best when it comes to refinement although admittedly i'am not that well versed in motorcycles and don't have much experience or benchmarks with other single cylinders to compare it with), my brother's Duke 390 feels smoother, atleast once past idle and lower rpms, my cousin's Himalayan too felt smoother no matter how much i hate to admit it. (Its an Royal Enfield afterall and that engine otherwise is pretty below average in most other parameters but it for sure is smooth)