Torque specs backwards?

[Rabbit]

The shop manual calls out for 40 ft-lbs on the front sprocket and 80 on the rear. That seems backwards. Is anyone aware if this is correct or was there a change needed? I do know that there was a correction issued on the valve clearance section after the first iteration was published.

 

[670cc]

I have noted this and even commented on it in a recent thread. 80 pounds-foot for the rear sprocket nuts clearly must be in error.

 

[Rabbit]

Is there anyway to contact Honda regarding this? Seems like they could be liable and would want to correct it.

 

[Rabbit]

I have a torque wrench. I guess I could see how much force it takes to remove the old one and go from there.

 

[670cc]

I have a torque wrench. I guess I could see how much force it takes to remove the old one and go from there.

The torque required to overcome the static friction while the nut is loosened will not likely be accurately indicative of the torque that was applied when the fastener was installed.

As for the torque for the rear sprocket nut, instead of using the 80 lb-ft spec, I sought the standard spec based on fastener size, which I think was listed in the general information part of the manual.

 

[INTHEWIND]

40 ft-lbs on the front sprocket bolt and 80 on the rear sprocket nut is what my manual says.
12 mm sprocket nut on the rear, should handle 80 ft pounds.
80 on the front bolt sounds excessive.

 

[670cc]

40 ft-lbs on the front sprocket bolt and 80 on the rear sprocket nut is what my manual says.
12 mm sprocket nut on the rear, should handle 80 ft pounds.
80 on the front bolt sounds excessive.

My 2012 Honda NC700X service manual Standard Torque Values tables shows a spec of 40 lb-ft for the 12 mm nut/bolt. The table does not agree with the text in the rear sprocket section; one is likely incorrect, or else the rear sprocket stud/nut are specially hardened metals. I used the 40 lb-ft spec, as from my experience, the 80 lb-ft value seems innapropriate for the sizing and for the application. I may be wrong, but I do not want to risk damaging the nuts and studs for the rear sprocket from over tightening.

The driving force at the rear sprocket is being applied to the studs on the carrier. It seems very odd to me that 5 nuts, that are mainly dealing with lateral forces on the rear sprocket, would have a greater torque specification than the single larger rear axle nut. But, that’s just my way of looking at it.

 

[INTHEWIND]

My 2018 Goldwing wheel nuts were 80 ft pounds of torque.
They were 12mm.
So I dont have any idea what the value should be.
I agree with your post.

 

[670cc]

My 2018 Goldwing wheel nuts were 80 ft pounds of torque.
They were 12mm.
So I dont have any idea what the value should be.
I agree with your post.

Good point about the Goldwing wheel studs. Next time I have the rear wheel off my ’02, I’ll check the stud diameter, but the parts listing does say 12 mm. In any event, the sprocket nuts are self locking, whereas wheel nuts are not. The risk of that NC sprocket coming loose at even 40 lb-ft is nil. The wheel, in my opinion, should experience far more lateral forces than a chain sprocket, and you certainly wouldn’t want a wheel coming loose. That’s all from just my armchair engineering gut feel.

 

[mzflorida]

This is a project that I need to do but have no experience in doing…that’s the predicate to my question. I googled the torque specifications for various Honda motorcycles. Some of the more current models have specs for the sprocket nuts at 80 foot pounds. Would that fact change any of your opinions (who are more knowledgeable than me) on this subject? I don’t know enough about all of the forces in play to arrive at any kind of a credible conclusion. That said, though possible, it is hard to imagine that the 80 value is repeatedly misprinted across many manuals.

 

[670cc]

This is a project that I need to do but have no experience in doing…that’s the predicate to my question. I googled the torque specifications for various Honda motorcycles. Some of the more current models have specs for the sprocket nuts at 80 foot pounds. Would that fact change any of your opinions (who are more knowledgeable than me) on this subject? I don’t know enough about all of the forces in play to arrive at any kind of a credible conclusion. That said, though possible, it is hard to imagine that the 80 value is repeatedly misprinted across many manuals.

For comparison, I checked my CRF250 manual. For what it’s worth, the 10 mm sprocket nuts are spec’d at 37 lb-ft torque. This compares to the Honda standard 10 mm bolt/nut torque value of 25 lb-ft. The 250’s rear sprocket torque seems to be 50% over standard, unlike the NC’s which is 100% over standard. Again, a curiosity, for what it’s worth.

As a matter of interest, I looked through all the other torque values on the NC700X. Only two bolts/ nuts were higher specified torque than the rear sprocket nuts, the 12 mm flywheel mounting bolt at 116 lb-ft, and the 18 mm clutch center lock nut at 94 lb-ft.

Does that all matter? Perhaps not.

 

[lootzyan]

I haven't changed the chain or sprockets on my bikes and I don't expect to have the opportunity to do so.
Many years ago (maybe 10 years) and I already forgot why, I put a note in the service manual next to the spec for driven sprocket nut torque - 80 lbf-ft - "Careful. It may be too high". Today this topic came back so out of curiosity I checked my copies of service manuals.
A trivial problem for me. I figured if I was going to do it today I would use the standard torque values recommendations as previously suggested by Greg.
But by chance I noticed in my garage the wheels of my Honda car have a very similar spacing between wheel studs as my CTX700 rear chain sprocket. They have the same diameter and M12 thread. Also the outer diameter of the rear wheel is similar. I checked the recommended wheel nut torque in the car manual. It is also 80 lbf-ft.
Without speculating why these values are the same, today I would follow the given recommendation for the NC/CTX - 80 lbf-ft.

 

[MZ5]

I think it's important to recall how different the sprockets are, and to recall how a bolted joint works.

The front sprocket is mounted on a splined shaft. That means the ONLY thing the bolt does is prevent the sprocket from sliding off the shaft sideways.

The rear sprocket isn't on a splined shaft, it's on a cylindrical hub and mashed against a smooth, flat 'plate' or surface. The threaded studs aren't there to be the things which transmit drive force to the rear hub (from the sprocket). They're there to work in combination with the 'lug nuts' to squeeze the sprocket against the hub (and center things, since the holes through the sprocket are tapered). The force from the sprocket and chain is transmitted to the hub (wheel) primarily by the friction between the flat planes of the sprocket and hub which are squeezed together very tightly by the 'lug nuts.' This is how joints of this sort work. The bolts themselves are NOT supposed to carry the shear force of the sprocket trying to rotate relative to the hub.

Because of this, the rear sprocket MUST have significant clamping force from the 'lug nuts.' The front sprocket needs nothing of that sort. It is thus sensible and expected that the rear sprocket lugs would need to be tightened more than that for the front sprocket. The fact that there are multiple 'lug nuts' at the rear makes it a more complicated comparison. I don't claim the specific numbers listed in the service manual are strictly accurate, but in principle the rear sprocket nuts SHOULD be much tighter than the front sprocket retaining bolt.

 

[Deleted member 1183]

Looked up my 2017 X-Adv manual. It also is 80Ft lb for the driven sprocket nuts. 40 for the drive sprocket. I have changed the chain and sprockets on my bike and I would have used these settings. No issue.

 

[Rabbit]

Sounds like 40 front and 80 rear is the winner

 

[INTHEWIND]

Thats what I would do too.

 

[670cc]

Sounds like 40 front and 80 rear is the winner

Sounds like a good plan.

 

[Rabbit]

I don’t think the specs are mis typed. 18-8 in the service manual covers rear wheel bearing replacement and also notes 80 ft lbs for torque on those nuts

 

[670cc]

I don’t think the specs are mis typed. 18-8 in the service manual covers rear wheel bearing replacement and also notes 80 ft lbs for torque on those nuts

I think you’re right. Plenty of evidence does point to Honda‘s intentions being 80 lb-ft, and owner’s should be advised to follow it.

I know next time I’m pulling hard on that torque wrench against those sprocket nuts, I’m not going to have the guts to put 80 on them. I will chose a lower value, but that’s just me, perhaps me alone. If I caused an unnecessary alarm over that torque value, I apologize (but I still don‘t like it).