Torque Spec for Rear Sprocket Bolts?

[PaulC]

yamaha oem. If i reuse this over, ill locktit it! with red. Had a heck of a time with the yz's over the years with rear sprockets stay put. After much expense, found OEM was best!. in this case. With the TR its the chance to tidy up one of the bikes few ugly areas.

 

[Mark_H]

Reading comprehension.

Chainring was loose when tightened to a reasonable amount. Fasteners must have been damaged in some way.

Matt

Well that proved to be incorrect did it not?
It was the thinner sprocket, not the fasteners, unless you refer the damage caused by over torquing them??

I am with Glitch on this one, my stock Sprocket Bolts have enough thread to compensate for a 1mm thinner sprocket and more.
Something must be wrong if yours are tight up on threads and the sprocket is still loose.

The type of Nut used is a locking Stove nut which can be re-used but not continually.
How many of us change sprockets on a continuous basis anyway?

Now we have a long old argumentative thread when all that was needed was 6 washers of at least 1 mm thickness, maybe.

 

[Matt Crawley]

??
Whatever type of self-securing nut is used has got nothing to do with the length of the bolt...at all.
As long at the locking mechanism sits on the thread, that's it.
Which part of the thread it sits on is entirely irrelevant.
If the replacement sprocket is thinner than the OEM and only the bolt thread is visible/ available to use the nut on, of course the stock nuts can be used!
My OEM bolts have enough thread windings showing to tighten a nut even if no sprocket is present at all!!
So what's the issue?

If my sprocket hardware worked the same way as yours then I would have had no problem.

My stock nuts and bolts would not hold the new (thinner) chainring tight. There was .5mm of free space between the torqued bolt and the chain ring. There were plenty of available bolt threads but the NUTS would not thread any further without applying torque in excess of 100lbft.

To me that indicates either the bolt threads were damaged or that the stock locking nuts can't be tightened past a certain point.

It appears the nuts in question are "Stover" or "Prevailing Torque" nuts. And are defined as follows:

Stover lock nuts are one piece, all-metal prevailing torque hex nuts with a conical top and a flat bottom bearing surface with chamfered corners. The locking action, created by distortion of their top threads, is said to be capable of withstanding severe vibration and shock loads.

By definition, "Prevailing-torque locking fasteners have a self-contained feature which creates frictional interference between the threads of the mating components." Consequently, unlike free spinning lock nuts, there is a resistance to rotation during both assembly and disassembly requiring them to be wrenched; that resistance is called prevailing torque. The advantage is that disassembly is unlikely even if preload diminishes completely because of the remaining rotational resistance.

The nuts spin freely until their distorted top threads engage the threads of the mating part. For the locking action to be effective, the locking element must contact fully formed threads so several threads of a standard bolt/screw should extend beyond the top of the nut.

Stover lock nuts are reusable a limited number of times because the prevailing torque declines each time the nut is used. Always follow the manufacturer's recommendations regarding nut reuse, thread lubricants and torque values. Do not apply standard torque values to prevailing torque lock nuts because the joint may not be tightened to the correct clamping force due to the additional friction of the locking element.


Generally, prevailing torque lock nuts are not considered suitable for long threaded assemblies because extended nut travel along the threads could damage the nut's locking feature or the mating threads. Therefore, the length of the bolt/screw should not be much longer than that needed to ensure full thread engagement with the nut.

Reading the above makes me think it should only take a max of 17-18Nm to thread the nut down the bolt. Unfortunately it required a lot more force than that to tighten past the stock location. If my replacement chainring was the same thickness I don't believe I would have had any of these problems.


Matt

 

[Matt Crawley]

Well that proved to be incorrect did it not?
It was the thinner sprocket, not the fasteners, unless you refer the damage caused by over torquing them??

Yes... er no. See my reply to Glitch above. Looks like thinner sprocket might have brought some damaged threads into play.

I am with Glitch on this one, my stock Sprocket Bolts have enough thread to compensate for a 1mm thinner sprocket and more.
Something must be wrong if yours are tight up on threads and the sprocket is still loose.

Plenty of threads and it appears that "Stove" nuts should be able to run down the whole thread length. Technically mine threaded down tight but it took 200lbft to get there.

The type of Nut used is a locking Stove nut which can be re-used but not continually.

Thanks for the name. I think I've seen that style of locker on turbo housings, headers, etc.

How many of us change sprockets on a continuous basis anyway? Now we have a long old argumentative thread when all that was needed was 6 washers of at least 1 mm thickness, maybe.

Nah. We have a vigorous discourse exploring the intricacies of Italian motorcycle design and how that relates to backyard maintenance.

Thanks for the feedback.


Matt

 

[robertaccio]

These Austrian machines are somewhat notorious for sprocket nuts coming loose. They are worth checking on a pre ride/race inspection regular basis.
Also although they are using self locking nuts, high strength type 271 red is a great additional insurance against them coming loose. Its about bullet proofing the machine.
In the Aero world we are held to the spec that no less tan 3 threads should protrude from nuts of any type, we use alot of prevailing torque lock nuts, along with many other types.