Fuji nut
 

This is a Fuji nut:


https://i.ibb.co/L85FgGb/Fuji.jpg


Yamaha use them on the rear axle of all the 700s (MT-07/XSR700/R7 etc) and possibly the MT-09 range too.


It acts like a Nyloc nut by way of that thin plate you can see at the top of the nut in the picture. I don't know why they use it although it is half the size of the axle nut on the SV and doesn't require any external locking but the SV has a plain nut and it isn't locked at all. Torque on both bikes are approximately the same at 105Nm (give or take).


There is a problem. The nut is supposed to be reusable and it is - providing the nut hasn't been seated for a while and/or the thin metal plate hasn't got dirty, then it gets interesting because it unscrews about 2 turns and then seizes. If you keep turning it carefully mangles the thread on the axle which is £70 (Fowlers say it has to be ordered from Japan).

I read about this soon after buying my XSR so I replaced it with a nut from Pro-Bolt but my friend with an MT-07 wasn't so lucky and needed a replacement axle when he replaced his chain (but found one at a breakers yard - £25). He's now bought a nut from Pro-Bolt too.

The nut sits in a recess/chain alignment guide so you can't cut off a bad nut before it destroys your axle.

Not one of Yamaha's better ideas imho.

Re: Fuji nut
 

That seems crazy. So the nut on the SV is reusable? What's to stop it backing off?

Sent from my Nokia XR20 using Tapatalk

Re: Fuji nut
 

From the look of the axle nut on the Gen 3 bikes, it has a similar little locking plate but I've had the wheel out quite a few times with no issues ...

Re: Fuji nut
 

I'm not sure this is universally correct.

Out of interest, I took a closer look at our bikes at the weekend (Wife's Pointy SK5 and son's recently acquired Curvy '99 X), and both have a nut like this on the rear swingarm.

Maybe your previous SV had the standard nut swapped for a plain nut? I'm not sure something with no anti-loosening component is a wise idea in the relatively high-criticality environment of rear wheel axle.

FWIW, my 1987 Yamaha FZ600 uses a castle nut and split pin, so perhaps this type of nut is a 'modern' phenomena that many manufacturers are moving to?

(Having said that, I'll be bearing your story in mind and making sure to clean thoroughly before loosening for wheel removal, though I don't recall ever having had a problem in the past. Hopefully minor slackening for routine chain adjustment will remain trouble free.)

Re: Fuji nut
 

I looked at my SV rear axle more closely, it isn't a plain nut but neither is it a Fuji nut. I bought the bike new in 2016 and have had the axle out a few times with no issues. I haven't read about anyone having issues here or on the US forum, whereas you can find people with the issue on the XSR and MT-07/FZ-07 forums.
(Google fz07 axle seized)