Rear Sprocket Torque seems wrong.

[foxtrot722]

Replacing the chain and sprockets of the 2015 FJ 09, 

The rear sprocket takes a 14 MM socket, the front sprocket takes a 30 MM

Service manual says 58 foot pounds for the rear sprocket nuts (14 MM socket) and for the front sprocket nut )30MM Socket) 69 foot pound. 

I did blue Loctite the rear and torque to 58 foot pounds, but after giving it some thought, I really believe that is way too tight and could damage the hub. That is really tight for a stud that small. 

The next day I looked in the front of the service manual and found a chart that shows 22 foot pounds for a bolt using a 14 MM socket. 

Am I missing something here? 

Anyone have any thoughts on this? 

Thanks 

 

Edited January 9, 2022 by foxtrot722

[skipperT]

No, you’re not missing something. This has been discussed previously in another thread. Various posters here have also tried to get the recommended 58 ft/lbs listed for the rear sprocket and stripped the threads of the hub. 

I’ll point out several things which I’ve mentioned before… Some of these items are not covered in the service manual but are from my own experience:

-the torque chart that you reference from the service manual states at the top that it is for conventional fasteners. That’s why you CANNOT use the 22 ft lbs spec. 

-The nuts are NOT a conventional nut. They are also not a nylock-type or a standard nut with a serated backing, or or anything like that….

I call them a U-lock nut and if you look closely you will see that there’s 2 metal “strips” imbedded in the outer part of the nut to grab and retain the tightness on the thread of the stud. Bad description but they are designed to stay tight.

IMHO these nuts should be replaced at every Rear sprocket change. Why Yamaha is still sticking to the torque spec and not indicating that the nut is one time use, is a mystery to all of us but is probably right there on the To-do list along with the recommended 5-15mm chain tension spec change…

-I would also argue that those that have stripped the threads are using junk torque wrenches or using them improperly. I set my (digital) torque wrench to 55ft lbs with new nuts and don’t have a problem. 
 

So in summary, order and replace the nuts if you think about it ahead of time, along with the nut which secures the front sprocket (because it is staked to the transmission output shaft and is also one-time use). You can set your wrench to 43 ft lbs instead of the factory recommended number if you wish, and a dab of blue loctite on the threads of either the threads or the nut doesn’t hurt. I would STRONGLY recommend using the 43 spec and Blue loctite if you REUSE the nut. 
(that 43 ft lbs number has been tossed around as it’s in the service manual of other models/brands when replacing the rear sprocket on those bikes which also use 10mm thread pitch fastener).

HT (sort of) Helps.  Rear sprocket nut torque on Yamahas often turns into a type of oil, thread. Grin…

-Skip 

Edited January 9, 2022 by skipperT

[foxtrot722]

Huge thanks Skip, this is a lot of very good information. I will be sure to order new nuts next time around. For now, I'm going to remove, clean the threads, use a little blue Loctite, and torque to 43 ft lbs. All of your notes make perfect sense. Thanks for taking the time to reply. On and BTW, having ridden dirt most of my life, I knew the shop manual chain slack information was way too tight.