Ben purchased the new Monty aluminum alloy cranks at UNICON for his trials uni. After UNICON, I wanted to make sure the cranks were on securely and used my crank installation method; lightly lube the axle taper, indirectly pound (using pieces of wood for protection) the cranks using a 3 lb. brass mallet, tighten the axle nuts, pound the cranks again, tighten the nuts again. Repeat for other side.
Last night at a performance after Ben jumped off the stage a couple times, approximately 3 feet, he noticed some familiar movement in the cranks, similiar to the feeling when he rounded out the Lasco’s square holes. Tonight we pulled the cranks off and, sure enough, we noticed the slight dimples in the metal around the square hole of the right crank where the hole was starting to twist around the axle taper. Ben weighs approximately 80 lbs. and hops right foot back. Don’t have the camera with me otherwise I’d post some pictures. There was once since UNICON that I found another quarter turn of the axle nuts so I pounded them and cranked on the nuts again.
Could be a number of reasons why this happened:
Ben has incorrect technique in dropping. He pretty much hits bottom and bounces out of it. I suppose 80 lbs. is enough when combined with acceleration due to gravity. He’s done several drops of up to three feet during performances and parades.
Cranks could have not been installed securely, but I doubt it because they were pretty tight before. I work on them pretty heavily following installation to ensure there is no play.
Monty cranks are not what they’re cracked up to be. Dustin K. had problems with Monty cranks at UNICON in that the crank’s square holes weren’t sufficient in size to fit the axle square taper correctly. Ours seemed to have a hard time being started onto the square taper but after some convincing, they relented.
We’re pretty bummed…no, actually more heartbroken. Ben used his own money to buy the cranks and $70 is a lot of money for a 12 year old. I think we’re going to find a multi-ton press, press them on and hope for the best. I worry though about pressing into the aluminum hole too much. What can happen? How much is too much? Why?
Now what? Where do we turn to next? Here we go again, victims of the “there just isn’t a good trials uni crank” syndrome.
My next attempt at cranks for 20" trials might be to cut down and re-tap some Kooka DH cranks. It’s either that or Profile. With the Kooka’s I could probably make them into 135’s which would be pleasing to me.
Ben, sounds like you’d better preserve the equipment and start learning to roll them thar’ drops. You’s a growin’ boy who ain’t done growin’ yet. (sorry about the drawl, I’m practicing for my trip to Georgia later this year.)
I am interested in this if you have it done. Perhaps others are also. If you’re going to have it done please post and if there is enough interest maybe we can get a batch modified all at once.
[QUOTE] Originally posted by yoopers
[B] I think we’re going to find a multi-ton press, press them on and hope for the best. I worry though about pressing into the aluminum hole too much. What can happen? How much is too much? Why?
Bruce,
That multi-ton press may split the crank as it is forced onto the taper (which is okay if you have reached the point of trashing them anyway). Just make sure it is supported by the other end of the axle instead of a hub or bearing surface. Don’t wanna trash the hub in the process!
Have you verified (with a torque wrench and thread specs) that you have the maximum torque that the threads can handle during your tapping and tightening process? It sometimes takes 5 or 6 repeats before the nut remains at max torque after I tap/pound on the crank.
Sounds like Ben might be close to the point of twisting the cranks even if you get them to stay tight. Maybe you ought to build him a uni with an ATV tire for suspension!
ok - don’t press them on whatever you do.
The chances are that the alu cranks are not heat treated in any way so you may be able to rescue them and infact improve them by CAREFULLY filing out the square hole in them. by doing this you can make them engage perfectly.
It’s worth noting that you shouldn’t file the hubs as they are likely to be case-hardened and you’ll blunt the file.
once you’ve done that just put them on as you do normally.
To press them on harder than you can drive them on using the screw thread in the nut will probably require a BIG press
With aluminum cranks you have to be careful that they don’t get loose. If you ride them while they’re loose, you’ll damage the taper on the crank.
The best solution is to make sure that they never get loose in the first place. You don’t need to press them on with a heavy press. Firm pressure with hand tools will be enough. Lightly grease the taper. A 12" c-clamp will generate enough force. A mallet and a block of wood will also do the trick and probably generate more force than the c-clamp. Keep grease off the threads of the retaining bolt. The retaining bolt will get Loctited on and grease on the threads will keep the Loctite from doing its job. Put red permanent strength Loctite on the retaining bolt threads and tighten it down.
The theory here is that as long as the retaining bolt does not back off the crank is going to stay tight. I’ve been Loctiting my retaining bolts and the Loctited bolts have not come loose on me. Keep those retaining bolts tight. Check them regularly. There is no need to re-Loctite the bolts when checking them for tightness.
I’ve fixed damaged tapers with Loctite sleeve retainer. Before you try filing the taper on the crank, try the Loctite fix first. Check the Loctite and Permatex web pages to find the flavor of sleeve retainer that would best fill the gap in the taper. You’ll want the permanent high strength stuff. You’ll still be able to pull off the crank with a crank remover even with the high strength stuff. When using the sleeve retainer on the taper do not use any grease on the taper. The sleeve retainer will take the place of the grease.
I fixed a poorly fitting crank with Loctite. Worked OK and kept the crank tight. The bad crank was on a street uni and not a trials uni. I think the Loctite fix will hold up on a trials uni, but I’m not sure. And remember to check the retaining bolts regularly, especially when using spendy aluminum cranks.
If the Loctite or Permatex doesn’t work then you can try JoeRowing’s solution and file the taper to a better fit. But it’s probably best to have a machinist do that kind of work.
I was reading Scott Bridgman’s site last night in his empirical muni page http://www.muniac.com/emuni.htm and under the “crank installation” info. Scott indicated that, even after torquing the retaining nut or bolt into place, with use the crank will still walk up the spindle some which says to me that, when that happens, the retaining hardware would not be tight anymore. Interesting info. I may be missing something here. If that’s the case, perhaps Loctite on the spindle will keep the crank from walking and thus keep the retaining nut tight. Reverse thinking it seems.
I like the Loctite sleeve retainer idea if it really works. Sort of like a Bondo idea? Sure hate to continue to ruin Ben’s hard earned new Monty cranks.
I still think I’m going to try installing the Montys with a press, only doing it very cautiously. I’ll try the Loctite sleeve retainer first.
Well, this past weekend, I took Ben’s wheel down to the maintenance shop at my place of employment and used the hydraulic 30T press to install his Monty cranks. I lubed the tapers with dry graphite, supported the opposite end on the axle and not the hub flange, and pressed the cranks in place. The press did not have a pressure gauge so once again, it was gut feel. I did press them on the spindle quite a ways with a LOT of pressure and then that twinge more. Often times, its the twinge more that gets me and blows things apart. This time, caution and gut feel won and the hub is fine. I wonder how much lateral force a hub can withstand before it buckles?
Then I tried to use the same method to install the cranks on my newly built Coker wheel but the wheel wouldn’t fit into the press. The nerve of the company to purchase a press that won’t fit a Coker wheel!!!
The nuts were installed with blue thread-lock and torqued to over 50 ft-lbs. John Drummond stated in an email to me that Unicycle.com torques the axle nuts to 700 in-lbs (or 58 ft-lbs). Once again the gut feel came into play and I “felt” that the thread stretch had reached it’s limit before I hit the 700 in-lb mark.
Ben has yet to test it because first, I have to repair a couple of loose seams in the Miyata seat cover, and secondly, he’s laid up with a soccer injury for this week.
More later after the Monty cranks get a road test.
That is very good info on Muniac’s site about crank installation. I think the big gottcha about installing cotterless cranks is that when the crank walks up the spindle it unloads the retaining nut a bit and then the retaining nut is free to loosen itself due to pedaling forces and vibration. Red Loctite on the retaining nut will keep the retaining nut in place even when the crank walks up the taper. As long as the retaining nut stays in place the cranks should stay tight.
That info jumped out at me too. If that’s the case, all axle nuts should be installed with some sort of thread-lock. I will use it from now on.
I do quite a bit of maintenance on the kid’s unis in our club (and on our own for that matter). The thread-lock, Permatex, Loc-tite, etc., is quite expensive when purchased at local hardware stores or even the local Wal-Mart for that matter…$3 - $4 for a .2 oz. bottle. I wonder if there’s a better deal out there somewhere? I can see going through quite a bit in a year.
The stuff may be like $3 for a .2 oz bottle. But when you only use a drop at a time that goes along way. And its tons cheaper than buying new crank arms all the time.
If you really do need more loctite than the little bottle supplies. Try going to an auto parts store and asking for it there. My auto parts sells 1 oz bottles, I forget how much for. But thats alot of loctite. I think the .2 oz would be fine for doing repairs even to lotts of unis.
