Crank issues

[jifdave]

I've had a giant Yukon mountain nkie for a few years now and I've managed to mangle several left crack arms. I think this is because the bolt comes loose and the movement makes a round hole from what was once square.
Also I'm 6'8 and just around 15 stone and 75lbs. (20 stone)
My

question is why does it keep coming loose and how can I solve it?
A: buy new bolts
B: buy a new bottom bracket(spindle)
C: I'm too heavy and it will keep breaking.
D: buy a new road bike.

 

[TheDoctor]

Bad luck.
The thing about square taper is, you tighten the crank on, and then after a few weeks you need tighten it again. If you don't, it eventually goes slack and then the hole goes round...
So, what I'd do once you fit a new one is this :-
Tighten it. No, tighter than that. Really tight.
Ride it for a fortnight. Tighten it again
Ride it for a fortnight and try and tighten it again.

 

[guitarpete247]

+1 for that. Keep checking it for coming loose. I have a neighbour with a similar crank problem. I tried to swap it the other day for an old one I've got. The problem is he's also horlicksed the threads in the crank arm so couldn't get my crank removal tool in. I didn't have enough time to work on it and he seemed willing to live with it as he only uses it to go 1/2 mile .

 

[rusty bearing]

Loctite on the bolt thread when assembling.

 

[I like Skol]

Loctite on the bolt thread when assembling.

Loctite on the spindle/crank interface. I was shown this by an LBS I used to frequent. The guy was a proper old-school engineer type and seemed to really know his stuff. Also, as mentioned above, tighten then tighten again and tighten one more time over the first few weeks.

 

[jifdave]

Thanks for advice. I've tried glue and tightening every day. Neither worked.

Would I be better to swap it for something like this http://m.evanscycles.com/products/truvativ/power-spline-bottom-bracket-ec008464

Is there another option to square/diamond?

 

[02GF74]

Thanks for advice. I've tried glue and tightening every day. Neither worked. ​

​

ETF happened to my post?​

glue ????
loctite is the stuff - studlocker is stronger than threadlocker.

I doubt weight is the problem as I reckon the top cyclists can put more force through the pedals than you.

​

​

 

[jifdave]

Loctite is a superglue.

Decided to buy a much better bottom bracket/crank set.

Probably hollowtech.

Thanks for the help.

 

[02GF74]

Loctite is a brand - they make syperglue and the tread/studlocker stuff + no doubt many other glueing and locking compounds. The loctite is this isnstance is referring to the product, much like hoover is used when referring to a vacuuuuuuuuuuuuuuuum cleaner.

The thread/stud locker stuff is not the same as super glue.

 

[Amanda P]

Just to clarify, once the square hole in the end of the crank is rounded (even a tiny bit), it will never stay tight on the bottom bracket axle again - no matter how much you tighten it. Jifdave will need to replace the cranks (not the bottom bracket axle - that's so much harder than the alloy cranks that it won't have deformed).

When coming to fit new cranks, the Doctor's advice is sound - they need to be seriously tight. They should also be checked periodically so that they never become loose.

 

[byegad]

Yes once it has any slack in it you need to re-tighten it and maybe, just maybe it'll be OK. But ride it a mile with any kind of movement and it's banjaxed.