Should I use Thread-Loc on my crank arm nuts or not, I ask this because I went out on a ride in late August and my bike developed a creaking sound, it turned out my non drive side crank arm had started to come loose, I tightened it up to the specified 50Nm, I went out last Wednesday and the same happened again, what I’m wanting to know is, is it safe to use Thread-Loc on the crank arm or will it cause issues later down the line please
To Thread-Loc or not to Thread-Loc, that is the question
- Thread starter EMTBSEAN
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Paulquattro
Meet & Greet Elite
Hi
A little blue loctite wont do any harm at all
A little blue loctite wont do any harm at all
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- #3
Is that the medium strength or high strength please mateHi
A little blue loctite wont do any harm at all
I've said it before, I'll say it again. Assembling aluminum or stainless fasteners dry is sloppy workmanship. Using oil or grease exhibits the knowledge that something needs to be done, but it's amateurish and not effective over the long run.
To answer your question more directly, yes, it's appropriate to use Loctite or a similar product on your crank arm fasteners. Medium strength will be your best choice. Proper cleaning, application, and cure time are important.
Personally, I'm more likely to use anti seize. It inhibits galling and corrosion better than a thread locker, and it allows for more precise tightening. Unless the project is disposable junk, I'll use anti seize on nearly everything.
Although there's a lot of fancy science surrounding threaded fasteners, they're not all that complicated for folks at our level. Properly tightened, fasteners don't just magically loosen. The problem with your cranks was more than likely improper fit, dirt, or galling. Address that, and live happily ever after.
The entire purpose of a torque setting is to maximise the friction between bolt thread and the female thread but to stay below the bolt's shear point. Properly installed there is a bsolutely no reason for that bolt to come loose. If it does you need to find the reason. Thread lock and/or anti seize are designed to combat specific scenarios such as high frequency vibration, heat or chemical influence, mix of different metallic materials. Thread lock is more typically used where torque values are relatively low either because the fixing screw/bolt is small, the material(s) being fixed are relatively weak ( e.g ally panel or plastic, or where a higher torque would impede the operation of a bearing or bush. Crank arm bolts are typically torqued to 50nm so should not need thread lock. The main criterea for fixing a crank arm is cleanliness. There is a case for using a little grease on mating surfaces such as the underside of the bolt head and the extractor surface on self extracting cranks.
The other thing to ensure is that the correct torque is applied. What may prevent that is a hopelessly inaccurate torque wrench or not using the correct technique with the torque wrench. The correct torque is achieved when the torque wrench "clicks" as the torque wrench is in motion.
If your crank has already worked loose a couple of times I would bin the crank bolt and get a new one since the existing one is likely to have some thread damage.
The other thing to ensure is that the correct torque is applied. What may prevent that is a hopelessly inaccurate torque wrench or not using the correct technique with the torque wrench. The correct torque is achieved when the torque wrench "clicks" as the torque wrench is in motion.
If your crank has already worked loose a couple of times I would bin the crank bolt and get a new one since the existing one is likely to have some thread damage.
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- #7
Many thanks for your all your responses guys, it’s given me plenty to look at and think about too, if I’m well enough I’m going to get my bike in my workshop tomorrow and have a look at it, not so good today so tomorrow 
I’ll be well enough 
I’ll be well enough 
Hattori-Hanzo
Well-known member
I had a crank arm that kept coming loose, turns out the Isis lugs inside the arm had worn slightly, (probably from riding the bike unknowing the crank was slightly loose) no matter how tight the bolt was, and even using thread lock it would work loose again.
Only way to fix it was to replace the crank arm.
Only way to fix it was to replace the crank arm.
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- Thread starter
- #9
Thanks for letting me know mate, I’ll check that too while I’ve got the crank arm off, I need to check the drive side too just to double check my chain ring is tight after reading some peoples posts about them coming loose as well, I’m covering all bases to make sure it’s not my motor that’s not at fault or at the end of it’s life
Hattori-Hanzo
Well-known member
What bike is it? Have you checked your motor mounting bolts? If they are loose it can cause a creaking.
Use Loctite 243 thread locker. Also paint tell tales - I use one of wife's nail varnish/polishes.
The left crank arm just fell off
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- #13
I’ve been in my workshop today checking my bike and the non drive side crank seems fine after I torque’d it to 50Nm, after checking the drive side I discovered that the crank arm bolt cap was not very tight at all, I checked the crank arm was set at 50Nm, tightened both caps and went for a spin and so far all seems fine, I didn’t use any Thread-Loc this time but if it does come loose again I will buy some new Hope crank arms and use a little Thread-Loc, thanks for all the help and advice I’ve received from everyone, much appreciated guys
Buy them books, send them to school, and all they do is eat the covers.
Dunabunk
Member
don't know if it'll work on crank arms, but on all other nuts and bolts, I use plumbers tape and wrap it around a few times, never had a issue with anything coming loose, however if you do loosen them, it can be a bit of pain removing old tape to put new on, but I've don't this for years and never had a problem
I'd never use thread lock on any part of a bike .
Light parts PTFE tape .( small bolts )
Heavy parts gas fitters PTFE tape ( crank bolts )
Put copper slip on is all i do if i bother with anything. . I can't say I've ever used loctight on the 15 bikes I've had and can't remember a crank ever coming loose. Saying that I never had a chain measuring tool or torque wrench etc etc till I got a Ebike. I do put some on the bolts that had it on on Levo. Maintenance has changed a lot since ebikes appeared.
darwink1
Well-known member
Locktite or no locktite, if you ride your ebike frequently and or aggressively you should be checking your bolts often. Just throwing a wrench on em quick, I do it before every ride, can make all the difference.
D
D
bsquared
Active member
Yes - but check often. I have a Yamaha YDX and I have lost bolts mid ride. So now I check before and after each and every ride. It is always the motor mounts... I have loctited them... but still!
E-MAD MALC
Well-known member
If your talking ptfe it's mainly used for sealing threaded joints not really to try and keep nuts or bolts tighten up
Dunabunk
Member
I know what ptfe is for but it does the job and like I say, I've never had a problem with it
Amber Valley Guy
Well-known member
Agreed, unless it specifically says assemble and torque dry then a drop of lubricant is the correct way to torque a fastener. The OP should also check the threads aren't damaged as 50NM is quite a high torque value.
- Thread starter
- #24
I know that’s what I thought too but it’s specified at 50Nm by Hope, I checked the threads and they’re all fine, I’ll find out if everything is ok when I go for my next ride
I fitted hope cranks 3 months ago no issues coming loose . I borrowed a torque wrench that goes to 50 as mine doesn't. Saying that I changed chainring last week and took crank off as I couldn't get pedal off . It was just put on tight without wrench this time. I get loads of pedal strikes I often wonder if that would loosen a crank but never has up to now. I don't check bolts that often and I'm heavy an̈d out loads. Someone quoted on here if it's got loctight on it and you keep checking it you are effectively changed it , plenty differing opinions on here for sure .I know that’s what I thought too but it’s specified at 50Nm by Hope, I checked the threads and they’re all fine, I’ll find out if everything is ok when I go for my next ride
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- #27
Yep you’re not wrong about the differing opinions mate but there’s a lot of people in here that know a lot more than I do about bikes so I’m grateful for the help, I checked all the mating surfaces, made sure there’s no galling, used some marine grease as it’s known for it’s anti seizing properties, checked all the threads, checked the crank arms for torqued the bolts to 50Nm and didn’t use Loctite, I’ve done just about everything I’ve been advised to do so if the crank arm comes loose again I don’t know what to do
Like you I'm no expert strange one that , I have heard of it before though. Hope are pretty good to deal with they have a technical department you can email or talk to direct. I broke a freehub a year ago my fault ,they replaced and rebuilt on warranty. Worth a phone call.Yep you’re not wrong about the differing opinions mate but there’s a lot of people in here that know a lot more than I do about bikes so I’m grateful for the help, I checked all the mating surfaces, made sure there’s no galling, used some marine grease as it’s known for it’s anti seizing properties, checked all the threads, checked the crank arms for torqued the bolts to 50Nm and didn’t use Loctite, I’ve done just about everything I’ve been advised to do so if the crank arm comes loose again I don’t know what to do
Just to add more!
You cannot tell if a thread is damaged just by looking at it. Over torque and a bolt rattling loose can spread the thread.
Checking thread locked bolts is fine but if the bolt is disturbed the thread lock seal will no longer be effective.
You cannot tell if a thread is damaged just by looking at it. Over torque and a bolt rattling loose can spread the thread.
Checking thread locked bolts is fine but if the bolt is disturbed the thread lock seal will no longer be effective.
darwink1
Well-known member
Putting a wrench on a bolt to see if it's still tight is not the same as retorquing it with a torque wrench. You're not disturbing any locktite if you don't turn the bolt.
If said bolt was found loose you'd be pulling it, cleaning the old thread lock off, reapplying and torquing to spec again.
D
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