[Ozninjaguy]

Try soaking the nut with some good quality penetrating oil. Spray it where the nut contacts the sprocket in short sprays 10 minutes apart about 6-10 times, give it one last good soaking and then allow the bike to sit over night. Try again with a long handled ratchet wrench with a breaker bar attached while you tap the socket with a hammer. Let us know how you go.

 

[Ozninjaguy]

This was a common complaint on the 650 Versys forum I belonged to. Kawasaki way over tightened that nut at the factory. I rode it for years at the proper torque spec without issue.

Yes - also a common complaint with the Ninja 650. There are a few threads somewhere here from years ago with guys having the same problem.

 

[Ozninjaguy]

Also, I know you’re supposed to replace chain and sprockets together, which I normally do, but I’ve done just the chain before if the sprockets looked good and 12,000 miles later when I sold the bike, they still looked good.

I've replaced many chains on bikes without replacing the sprockets. If you maintain the chain well, and replace it before it's completely flogged, then it wont damage the sprockets.

 

[Ozninjaguy]

I was told 27mm, or the US equivalent (1 and 1/4 I think?). Neither fit the bolt just right.

What I often do in situations where there is some play between the socket and nut is to cut up a feeler blade, fit it inside the socket, and then tap it onto the nut. You can try different size blades until you get a nice tight fit.

A bit of a backyard fix it - but it has come in handy many times, especially with nuts that have a few rounded edges.

 

[Ozninjaguy]

That is a fantastic idea! I'm keeping that one in my back pocket for future use!

I meant fit it inside the socket - but I'm sure you got the gist of it.