Torque Spec for Rear Sprocket Bolts?

[Matt Crawley]

Hey Everybody.

I'm putting in a new sprocket and the stock nuts/bolts proved quite difficult to tighten.

I have an electric impact wrench that drives at roughly 50/100/200 lbft and it could not tighten the bolts enough to eliminate play at the 100 lbft setting. It drove them tight with the 200 lbft setting but then the last bolt I tightened snapped.

I couldn't find a torque spec in the Workshop Manual. Any thoughts from the group on this?



Thanks,
Matt

 

[Trenchcoat85]

17lb/ft IIRC? Something is wrong.

Clean both surfaces.

 

[CarstenB]

19Nm is listed in the workshop manual which converts to 14 ft lb.

 

[Trenchcoat85]

do you have the sprocket so the countersunk heads fit into the countersunk holes? (clean these out also).

I would never tighten a bolt, in a situation like this, so tight that it snapped. Look for warpage or distortion on the sprocket now. These shoulder bolts typically are not supposed to be re-used but I do- especially on my italian husky where they're about 3mm longer then every other dirt bike in the world. Maybe on your Terra also; but I kinda doubt it. Usually sold in sets for about $10-15. If you need the longer ones, just use stock japanese bike ones and leave the washer out. The locking tabs on the nuts will just get to the first threads.

and as always: any pics?

 

[glitch_oz]

Hey Everybody.

I'm putting in a new sprocket and the stock nuts/bolts proved quite difficult to tighten.

I have an electric impact wrench that drives at roughly 50/100/200 lbft and it could not tighten the bolts enough to eliminate play at the 100 lbft setting. It drove them tight with the 200 lbft setting but then the last bolt I tightened snapped.

I couldn't find a torque spec in the Workshop Manual. Any thoughts from the group on this?



Thanks,
Matt

100lbft on a little 8mm bolt? With an impact wrench?
No wonder at least one of them snapped at 200....they all should've popped.
There's a good chance that they're now stretched (those that still held), I'd also check for cracks in the alloy cast of the sprocket carrier, starting at the bolt-holes and radiating out via the eyelets of the cast.

Those are Nyloc nuts (self-securing) and should go on easy until the plastic ring at the back grabs, then have some consistent resistance until they bind and seat.

After that it's about 1/4 - 1/2 of a turn.
Only ever do them up by hand-tools (preferably 6-point sockets to prevent slips/ rounding off etc)...which also goes for anything involving alum in one way or another.

I'd suggest to remove all bolts and replace them.
They're pretty common M8x40mm length / 13mm hexhead and Nyloc nut with an S/S washer.
They are not a stretch-bolt (single use variety) AFAIK
No countersunk on either the sprocket (OEM) nor the carrier.

 

[Mark_H]

Impact Wrench Madness - Mine go hand tight with normal wrench and a bit of Loctite Torqseal, never had a problem.

 

[Big Timmy]

For those who have no idea how much to tighten a particular fastener and can't seem to find a torque spec for common size metric fasteners in the manual.

It might be a good idea to just look up a standard Metric Torque specification chart off the internet, print it and hang it up in your workshop to be a source of reference.

You may find some variation between some of these charts and the others but it's a good idea to have this information handy instead of just guessing and it beats snapping off bolts and stripping threads.

Here's just 1 of those charts. You can find them printed with specifications in Newton Meters of course right alongside its equivalent setting in Ft. lbs. and inch lbs. depending on what kind of torque wrench you happen to have.

 

[Matt Crawley]

I would never tighten a bolt, in a situation like this, so tight that it snapped.

NEVER broken a bolt? Congrats on your superior skill.

Look for warpage or distortion on the sprocket now.

Doubtful. The parts were spotless clean and torqued down the bolts in a star pattern.

These shoulder bolts typically are not supposed to be re-used but I do- especially on my italian husky where they're about 3mm longer then every other dirt bike in the world.

That was probably the real question. Can I re-use the sprocket bolts? I have used single use locking nuts on exhaust headers before and to me that is what these nuts look like. Terra's bolt ends are NOT conical.

Maybe on your Terra also; but I kinda doubt it. Usually sold in sets for about $10-15.

I looked for stock replacements but the price in the parts catalogue scared me away. Over $5 EACH!
Matt

 

[Matt Crawley]

Impact Wrench Madness - Mine go hand tight with normal wrench and a bit of Loctite Torqseal, never had a problem.

Reading comprehension.

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



Matt

 

[Matt Crawley]

100lbft on a little 8mm bolt? With an impact wrench?
No wonder at least one of them snapped at 200....they all should've popped.

My electric impact wrenches generally DON'T break the bolt, even on high torque settings. This was the first one in a long time.

There's a good chance that they're now stretched (those that still held),

I would guess that they definitely did stretch. I can see more threads than with the stock sprocket. Perhaps the new sprocket is thinner...

What's up with the weird insinuations? "At least one of them snapped..." "Those that still held..."? Do you doubt the information I am providing?

I'd also check for cracks in the alloy cast of the sprocket carrier, starting at the bolt-holes and radiating out via the eyelets of the cast.

You think the hub and sprocket could be damaged by squishing? Interesting... I'll take a look.

Those are Nyloc nuts (self-securing) and should go on easy until the plastic ring at the back grabs, then have some consistent resistance until they bind and seat.

Mine are not Nyloc or at least not traditional Nyloc. No ring on the end of the nut. I thought they were assembled as bolt/lockwasher/nut.

Only ever do them up by hand-tools (preferably 6-point sockets to prevent slips/ rounding off etc)...which also goes for anything involving alum in one way or another.

That's how I started. It was easy to get the nut torqued. It's just that the sprocket was still rattling around loose.

I'd suggest to remove all bolts and replace them. They're pretty common M8x40mm length / 13mm hexhead and Nyloc nut with an S/S washer. They are not a stretch-bolt (single use variety) AFAIK No countersunk on either the sprocket (OEM) nor the carrier.

I was thinking that would be the end solution. I'll post up some photos tonight.

Final question - Where did you guys find the torque spec for the sprocket? I could not find that in the workshop manual.




Matt

 

[Matt Crawley]

Turns out the new sprocket is roughly 1mm thinner in the clamping area. That means the stock nuts are engaging threads that were previously unthreaded.



Comparison of stock sprocket bolt threads to sprocketcenter, Superlite sprocket bolt threads.



No visible damage from over-torquing the bolts.




I'll check on the nuts in a little bit. I'm thinking they are locking nuts and not nyloc.




Matt

 

[Matt Crawley]

It might be a good idea to just look up a standard Metric Torque specification chart off the internet, print it and hang it up in your workshop to be a source of reference.

Here's just 1 of those charts.

View attachment 89157

Thanks Timmy.

I understand the torque values and the bolt spec but what is the torque spec referring to? Max recommended tightening?



Matt

 

[glitch_oz]

What's up with the weird insinuations? "At least one of them snapped..." "Those that still held..."? Do you doubt the information I am providing?

Not at all.
Just very surprised that not more/ all of them popped with that torque applied. 200 lbft is around 270nm.....a 32/40mm countershaft sprocket nut typically torques at less than half that.

You think the hub and sprocket could be damaged by squishing? Interesting... I'll take a look.
Mine are not Nyloc or at least not traditional Nyloc. No ring on the end of the nut. I thought they were assembled as bolt/lockwasher/nut.
Final question - Where did you guys find the torque spec for the sprocket? I could not find that in the workshop manual.
Matt

"Squishing" of hub/ sprocket not so much.... but bursting or cracking of the sprocket carrier lugs, being an alum cast, is a possibility with
sufficient pressures involved.
I used "Nyloc" as a generic term...they should be self-securing nuts of some name/ description.
https://goo.gl/u7tg1V for the torque values....it's 19nm= 14lbft
so it matches the posted torque table above for an 8G/ 8mm bolt pretty much perfectly.

 

[CarstenB]

Final question - Where did you guys find the torque spec for the sprocket? I could not find that in the workshop manual.
Matt

http://www.endurofactory.nl/pdfs/2013/2012_WSM_TR_650_Terra-Strada.pdf

page 137

 

[Matt Crawley]

http://www.endurofactory.nl/pdfs/2013/2012_WSM_TR_650_Terra-Strada.pdf

page 137View attachment 89176

I saw that but I thought that was for the front sprocket. Everywhere else it says "rear" when there are two.



Matt

 

[Matt Crawley]

Update:

The stock nuts are "oval" at the top and "lock" due to being forced round as they are torqued down. I imagine this provides similar locking security to Nyloc but will not wear out after repeated install/removal. This also requires the bolt to be exactly the correct length or it is IMPOSSIBLE to obtain the correct torque AND correct tightness.

Moral of the story: If you use a sprocket that is thinner than stock – the stock nuts can't be used.



Matt

 

[Trenchcoat85]

Update:

The stock nuts are "oval" at the top and "lock" due to being forced round as they are torqued down....

are you talking about stover nuts?

if so, you can feel them when you remove them by hand (not, of course, with an impact wrench- another reason not to use one... especially on a through-bolt with a nut). They have a somewhat limited use life, but usually more than nylocs.

 

[CarstenB]

i'd probably use additional washers to compensate for a thinner sprocket.

 

[robertaccio]

tight with locktite 271 red......

 

[glitch_oz]

This also requires the bolt to be exactly the correct length or it is IMPOSSIBLE to obtain the correct torque AND correct tightness.
Moral of the story: If you use a sprocket that is thinner than stock – the stock nuts can't be used.

??
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?

NO Loctite needed on a self-securing nut either (which is the whole idea of the thing, right?)

Anyone doing their own maintenance and spannering on their metric bikes should have a box of M4/5/6/8/10mm Nyloc-nuts floating around the garage shelves (or whatever other name/ brand floats your boat)