I was on my 8th trail ride on a Nimbus I got barely a month ago when I noticed some loose movement in the left crankarm. Not wanting to damage my hub I walked back to my truck and tightened the bolt as much as I dared and tried again. Not 20 yards from my truck it came loose again. Do I keep cranking down on the bolt risking a stripped hub? Locktite? Worst part is there is rain in the forecast for the rest of the week and here I sit…
Make sure you have grease on the axle before you install the crank. The grease will allow you to tighten the crank more then if the axel was dry. You were smart not to ride after the crank became loose. If you ride with a loose crank, you run a very high risk of rounding the square taper on the hub and cranks.
I would suggest riding with a socket wrench to tighten the cranks whenever they come loose. The problem will probably stop after a few more rides.
Daniel
I had this same problem with the same uni when i changed cranks to 170’s. I would have to tighten the bolts every 30 minutes. I pulled the cranks and put some “permanent” lock tite on the square part of the hub and haven’t had a problem since. I was afraid to put it on the bolt threads and do find that I have to tighten these periodically. But the cranks have remained tight. Should I put some on the threads as well?
Thanks, never even thought of trying to grease it down, but that makes sense. I can see the line where the crank was orginally and I haven’t made it back to that yet. I was just too worried about overtightening it. Looks like the sun is coming out so I might have to take the wrench and go ride again.
Grease is the magic cure then?
It’s always worked for me; I use vasaline cos I don’t know what kind of proper grease is appropriate.
Also, I use a few taps with a hammer (protecting the cranks etc with wooden blocks) to get the crank fully on.
The advice to carry a wrench for first few rides is good.
Just returned from 8 miles of trails, and the first 3 miles was a constant battle. At first it came loose easily and often, but as time went by I’d just check after a UPD. Did the final 4 with no adjustment needed.
Re: Help! Loose crankarm
In addition to grease on the crank arm, you can also use grease on the
threads. That makes sure that as much as possible of the force you’re
applying goes into tightening the cranks.
Tapping with a hammer? WARNING!! Only very light taps are OK. But as
soon as the nut engages enough of the thread, don’t use the hammer any
more. The sudden force of a hammer blow is likely to cause haircracks
to arise near the four corners of the crank hole, and once this
begins, the cracks tend to grow due to the forces of riding and even
of tightening. It is the beginning of the end for your crank!
The crank nut is not easily overtightened. For most systems, the best
tightening torque is around 40 lbs.ft. If you don’t have a torque
wrench, you can use a normal wrench of 1 foot long and lean on the end
with a weight of 40 lbs. Or a half foot long wrench and lean with 80
lbs, etc. This is probably not easy to do exactly, but it gives an
idea about how tight the nut should be.
Now that I think of it, maybe you can put the uni on a bathroom scale.
Use a non-digital one, because most digital scales need a stable
weight to display a value at all. Then orient the wheel such that you
push down vertically on the wrench. Don’t push or pull on the uni
while tightening. Subtract the weight of the uni + half the weight of
the wrench for extra precision…
Klaas Bil - Newsgroup Addict
“I (…) made it without dying, which means mere mortals can do it. - John Foss”
So then, is the locktite not a good idea?
Here is a past thread on installing crank arms: Cranks (yet more)
The main trick is to use a torque wrench. It is very hard to estimate what 40 foot-pounds of torque is. The only way to know is to use a torque wrench. If you are only using a standard socket wrench you are probably not getting the cranks on tight enough. The torque wrench takes away the guesswork.
Grease, Loctite, Torque Wrench.
Grease or Loctite works fine on the taper (the flat square area). Both grease and Loctite will act as a lubricant while installing the cranks. And that’s what is needed.
Loctite on the threads is a good idea. That keeps the bolt or nut from backing off and loosening up on its own. If the nut stays tight then the cranks will stay tight.
I would have to say the main answer to my problem was lack of torque. It wasn’t that I couldn’t do it just that I was fearful of overdoing it. But using a 7" ratchet I doubt if I was getting 40 ft/lbs on it, and I am trying to find a friend with a torque wrench to check it. Thanks for the help guys since knowledgeable unicycle repairmen are hard to find…