Rail (625Wh) Rail 7, chain ring nut came loose

[andrewgc]

No big deal, but after owning it for 1.5 years, 850 miles, I'd thought it prob wouldnt come loose on its own.
Hopefully the blue Loctite will help. Rode it 25 miles yesterday, and still tight.

 

[Zed. (Justin is short)]

all of the locktite

on my rail I'd check that nut every ride as its a common issue

Rich.

 

[Mikerb]

all of the locktite

on my rail I'd check that nut every ride as its a common issue

Rich.

probably far more common if the chainring is ally rather than steel since that is the only agent likely to loosen the locknut assuming it was torqued correctly in the first place and an ally chainring will have more flex especially after when well used.............it has been fine for 1.5 years in the post a bove so looks like it was properly torqued initially.
The ISIS crank thread is steel whilst the lock nut is ally.......... and it has very few threads yet is torqued to 25 to 30nm. It means the locknut is torqued very close to its sheer point with the thread pitch stretched to achieve maximum friction. That in turn means once it has come loose it is scrap. Its only c £10 for a new one. Blue Locktite might work for a while but it is not a permanent fix.

 

[andrewgc]

probably far more common if the chainring is ally rather than steel since that is the only agent likely to loosen the locknut assuming it was torqued correctly in the first place and an ally chainring will have more flex especially after when well used.............it has been fine for 1.5 years in the post a bove so looks like it was properly torqued initially.
The ISIS crank thread is steel whilst the lock nut is ally.......... and it has very few threads yet is torqued to 25 to 30nm. It means the locknut is torqued very close to its sheer point with the thread pitch stretched to achieve maximum friction. That in turn means once it has come loose it is scrap. Its only c £10 for a new one. Blue Locktite might work for a while but it is not a permanent fix.

Thanks, good info. In addition to alloy nut and steel crank threads, the crank is splined thereby eliminating half the threads. So yes, at 25+nm torque that prob right at the shear strength of the threads.
I will order a couple of new nuts, one for a spare.
When I do install the new one, would you suggest red Loctite (272/3), or none at all?
I do appreciate your input.
Thanks, Andrew

 

[andrewgc]

all of the locktite

on my rail I'd check that nut every ride as its a common issue

Rich.

Thank you. I marked the nut postion with a white paint marker when new, and checked it every ride. I guess after a year or so, I kinda quit checking it. My bad.
Thanks, Andrew

 

[Mikerb]

Thanks, good info. In addition to alloy nut and steel crank threads, the crank is splined thereby eliminating half the threads. So yes, at 25+nm torque that prob right at the shear strength of the threads.
I will order a couple of new nuts, one for a spare.
When I do install the new one, would you suggest red Loctite (272/3), or none at all?
I do appreciate your input.
Thanks, Andrew

Just make sure all threads are clean. I have never seen a spec but i suspect the torque setting is for a dry thread.....locktite or grease will cause over torqueing in that case. As you could probably tell it was not locktited originally.

 

[irie]

Plenty of info in the below thread:

Bosch Gen 4 Chainring Nut printed Torque of 25 to 30 NM is likely wrong

After following Bosch instructions (grease don't loctite) the chain ring lockring nut to 25 to 30 NM and having it fall off 3 times I was pretty annoyed and about to start looking into drilling it out and using safety wire. I even went to the local Trek Dealer and had them torque it down in case...

www.emtbforums.com

 

[andrewgc]

As you could probably tell it was not locktited originally.

Oh Duh, very good point.
ac

 

[Stihldog]

There was bulletin from Bosch to increase the initial torque for a new castle nut…from 25nm to 35nm. Lock tight may not be necessary when installing a new castle nut…but if you plan on using that nut a second time …then yes. A small swipe of blue loc-tight on the female threads only.

You might get away with using a castle nut once or twice …but you still risk the chance of it coming loose.

I keep two spares ($6-10 each). And the new increased torque, on a new nut, can help.

 

[Mikerb]

blue locktite really only acts as a type of glue. It is mainly effective for nuts/bolts fixed with low torque or higher torque nuts/bolts subject to vibration. Higher strength threadlocks need a pre treatment on non ferrous nuts/bolts ( eg ally) to bond properly and invariably requires heat treatment to break that bond when a nut/bolt needs to be removed.
The likelihood with the chainwheel lockring, is that very small deformations of the chainwheel levers it off. Seems to happen far less with a spider and BCD chainwheel than a DM chainwheel.