No matter what I do, the bicycle euro crank arms keep coming loose on my unicycle.com hub.
I’ve lubed the cranks, hammered them on and used loctite blue on the bolt.
Anybody have some advice? Is it time for loctite red?
Mike
Hit the gym and invest in a looong socket spanner!
Definitely not. This is the way to ruin your hub and wheel.
Check the cranks to see if they are mushing or rounding out. Try other cranks. When in doubt, get new cranks. They cost much less than a new wheel.
Hammering on cranks is dangerous because of the consequences of a miss, and it is completely uncalibrated. Grease the tapers and torque the nut on to 40 ft-lbs. This will draw on the crank as squarely as it is possible to do so. Blue loctite on the nut as you have been doing. If this does not work for you, change cranks, not the procedure.
I noticed that the UDC hub tapers are not as smooth as the Suzue hub tapers. Could this have something to do with it?
After installing new cranks, I re-tighten them a lot just to make sure they are seated. while I’ve never had a crank come loose on a UDC hub, they do seem to take more repeated tightenings before they are seated completely. I thought that it was from the ridges on the tapers.
Joe in Iowa
Thanks for the reply. After speaking to one of the guys at myLBS, I think maybe I already ruined my cranks 
I have some cheepies laying around. I’ll give them a shot. Maybe time for a torque wrench too.
I noticed that too.
The UDC hub and BE cranks will probably be my new Coker set up. Just wondering- did you have to tweak the frame to accept the UDC hub? I currently have a Suzue which I think is slightly narrower.
This hub is actually on a sem XL(W?), which coincidentally previously had a Suzue hub. I had the pull the forks apart very little. I have a reconditioned coker with a stock frame that came with a schwinn hub which is significatly wider than the UDC which is wider than the Suzue. In other words, you’ll be just fine.
…Still losing the battle.
I have new cranks and two colors of loctite on order, but I got anxious and wanted to be able to ride this unicycle in the meantime.
I installed a pair of these el-cheapo crank arms using some anti-seize on the tapers with no hammering and no loctite (i’m out). I figured I’d just keep tighening the bolts each time they came loose hoping they’d eventually settle into place.
The right-crank got loose right away, so I pulled my socket-wrench out of my rear pocket and tightened it. This happened a few more times, until I bent the left crank arm hopping up a curb!!! ARRRRGGGHHHH!!!
The cranks were brand new and lasted less than 15 minutes.
i know you’ve heard the whine on splined, and i won’t bore you too much with it, however, since going splined i have only had to tighten a couple of times. no more loosseneing during rides, no more expanding holes, no more bending… and i was running BU’s on a suzue before.
john
Oh yes I have. I have a KH and a summit as well. I’d love to put profiles on this thing…its only a matter of $300.
when i was still riding square tapered i had to always take a wrench because the crank arms came loose usually several times during a muni ride. not a problem though, i would just dismount, give a half turn, and be on my way.
Those who have not used a torque wrench likely do not realize how tight this is. It is TIGHT
I was surprised how tight it was. First time I used a torque wrench I had just tightened the nuts down hard with a socket wrench, and thought, “I’ll get out my torque wrench and see just how tight 40 ft-lbs is”. Using the torque wrench I immediately discovered how untight the nut was; and I had just tightened it. Using the torque wrench, I turned the nut about 2 more full revolutions before reaching 40 ft-lbs.
IMHO: If you use a typical 3/8" drive socket wrench, and are a medium sized guy, and you tighten it down hard, you are likely only tightening it to 25 or 30 ft-lbs; the handle on the wrench is just too short to provide the leverage needed to tighten the nut completely. Use a torque wrench; they are not expensive (they cheaper than one pair of BE cranks). They are less expensive than one set of cranks; examples:Sears beam style for $20US, HarborFreight clicker style for $16US
Thanks for the comment duaner. Strictly speaking, you should have loosened the nut before using the torque wrench on it. Here is a comment from the User’s Manual for my Sears Craftsman Digitork:
- Never torque a fastener that is already tightened. Loosen it first, then re-torque to the desired value.
The typical Craftsman lifetime warrantee does not hold for this wrench, though; it’s only 3 months for replacement and 1 year for repair.
Before I started riding a splined MUni, I took to carrying a Park 14mm crank wrench on all rides. Tighten at beginning of ride, and maybe check tightness at mid-ride. Wrench was handy if someone else needed it too.
I did this because I was usually riding on a pair of 20 year old cranks off and old Miyata (150mm IDOLs). The more times you put them and on and take them off, the more they’ll wear. Not to mention the more you ride them when loose. If you’re riding cotterless, keep the wrench handy at all times!
For best results if you’re doing lots of hopping and dropping, save up for something splined. That’s why the top unis have them. You’ll eventually pay for them in not having to replace parts. But long befor that, you’ll repay them in reduced frustration!
My current method, since I’ve been too cheap to buy a torque wrench, is to screw them on nice and tight, then do a few minutes of riding and tighten again. Repeat this until they stay tight. Only then should you take the cycle on a “real” ride, but bring the wrench along. Tighten occasionally during the ride, again until the nut stops tightening. This is not as effective as the torque wrench being used as directed, but keeps you close to your wrench, and mindful to make sure they’re tight. Especially if your cranks are old!
Those old cranks will next go onto my new 29er for the 24 Hours of Adrenaline this weekend. Someday I’ll get some newer ones, but those alloy IDOLs are holding up great!
I have had the same problem with Euro cranks, I think they are machined too tight for my stock coker hub; they dont slide on all the way. I have the nuts tightened as much as I dare and they have been staying snug, but I know that someday they will come loose a few miles out on a trail.
Has anyone tried filing some metal off of the cranks or the tapers?
carjug
I had the same problem on my Norco cheapie, sorry uni and found the taper was too steep on the hub, so making it easy to work loose. I took a file to each of the faces to reduce the angle slightly and this seemed to work (no loctite either). It takes a little time but it’s worth it if you’re looking at potentially buying anew hub. Good luck.
I never seem to have a problem with cranks coming off once they’ve been on a while. If they come loose, they come loose within a few miles of me installing them. I normally put them on, ride a bit (a mile or 2) then tighten them, repeat a few times until it doesn’t seem possible to tighten any more without doing damange, then leave them. I generally take a spanner with me, but haven’t had to use it much. That’s with BE’s on a standard hub, and a pedal spanner so it’s a bit longer than a normal 15mm spanner.
Am I right in thinking it’s more of a problem with alloy cranks? Might invest in a set when the current BE’s get a bit more twisted, but if I’d have to tighten them all the time that’d put me off.
John
As mentioned earlier in John’s post, riding on loose cranks ruins them. It’s absolutely amazing how much pressure the corners of the spindle exert on the inside faces of the crank taper when they are not pulled tight. One or two pedal strokes while even a little bit loose is enough to permanently deform the faces. After that the only way to make things right is to re-machine the faces.
A little math:
50 kg (about 110 lbs) on a pedal it is about 500 Newtons of force. That 500 Newtons, on the end of a 150 mm crank, makes 75 Newton-meters of torque.
The corners of the spindle are about centimeter away from the center of the spindle, so that 75 N-m torque puts a reaction force on each spindle corner of places a reaction force of 1875 Newtons on each corner (75N-m / 0.1 m = 7500 Newtons, then divide by 4).
Since the corners aren’t facing in the direction of rotation there is a “wedging” factor to consider. When the face is 45 degrees off from the desired force direction it takes 2640 Newtons of contact pressure to make the 1875 Newton torque reaction force.
When the crank is a little bit loose the contact area is perhaps 1mm wide and part of the length of the taper, let’s call it 1 cm, or about 0.00001 square meters. This contact area increases as the spindle digs into the crank, but by then the damage is done. For pristine cranks it’s really small.
Pressure is force divided by area, so 2640 Newtons of contact pressure divided by 0.00001 square meters is about 264 megaPascals (38,000 psi).
The strength of aluminum parts depends on the alloy composition and how the metals are formed. Cast aluminum deform permanently around 80 to 350 MPa, depending on the alloy and the casting and heat treatment processes. Forged aluminum tends to be stronger, yielding at from 150 to 450 MPa.
When the pressure from pedaling, which is going to be around 200 to 300 MPa for normal pedaling on a loose crank, exceeds the yeild strength of the material, which for cheap cranks is going to be at most 150 to 200 MPa, the edges of the taper dig into the crank and create pockets. Your crank is now damaged. Digging these pockets increases the surface area of the contact patch, so the force is distributed over a larger area and the pressure reduces. When the pressure falls below the yeild point for the material the denting process stops.
When you figure in the fact that the torque reactions won’t be evenly distributed, then one or two taper corners could easily create 400 to 600 MPa of pressure under normal pedaling. Do any extreme riding, like a big drop, and the corners of the spindle could dig in with pressures over 2,000 MPa. Even hardened steel would have problems at those pressures. In aluminum it makes some pretty substantial dents.
Now if the cranks are in good shape (flat to the taper) and installed properly the reaction surface is much larger. When cranked down tight there is perhaps 20-30 times more surface area in useful contact. This reduces the pressure by a similar amount, so that potentally crank-killing 2000 MPa is reduced to only 60 -100 MPa, which is within the yield limits for even cheap crank material.
This is why good quality cranks, machined to match the tapers and properly installed, tend to last.
And it’s also why damaged cranks won’t ever stay on no mater what you do. Once the faces inside the crank are deformed it becomes impossible to get that nice, broad contact between the tapers and the cranks. Go ahead and pound them on with lock-tite. You’ve got nothing to lose. They’re already junk.
Hope it helps,
Tim
Re: Me against the unicycle.com hub and bicycle euro cranks
On Fri, 14 May 2004 08:38:36 -0500, “carjug” wrote:
>Has anyone tried filing some metal off of the cranks or the tapers?
Someone has probably tried this, but I would think that I can’t file
flat enough. Obviously, you don’t want to round the tapers’ faces.
Cranks: maybe easier. Also, these are really hard materials by design
so I think they will be difficult to file (flat or not).
Klaas Bil - Newsgroup Addict
be sure to remove the saddle and simply sit on the seat post. this is far more comfortable - tennisgh22 on the comfort of Savage unis