Keeping crank bolts tight.

DrGooGoo

Dirt Disciple
I have a vintage Cannondale (1986 SM600).
The bolts that hold the cranks tight come loose after hard pedaling.
Any suggestions for keeping them tight?
Should I install new crank bolts or maybe some lock tight?
Has anyone else had this problem and fixed it?
 

Osella

Senior Retro Guru
Re:

Loctite can be a solution. Another might be a slight incompatibility between tapers.
JIS and ISO aren't quite the same, and older machinery can be more susceptible to the difference in tolerances.

Have you changed the BB recently, for example?
 

2manyoranges

Senior Retro Guru
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that's absolutely right about tapers. But a few other things should be ruled out too.

1 never grease the tapers - degrease them with isopropyl alchohol/brake cleaner
2 check there's no rounding caused by the cranks having been used whilst loose.
3 check there's no lip on the bb caused by over tightening
4 check that the washers are the right type and aren't made of cheese or the wrong size
5 check that the bb or the crankset isn't made of cheese and that the bolts are tightening against the end of the axle rather than against the body of the crank

Note that in the early 90's I had one of the most expensive cranksets available the Mavic MTB triple. This was made of ridiculously soft alloy and came loose all the time, each tightening saw it climb higher and higher up the BB axle until you were tightening against the axle. Rubbish QC.
 

DrGooGoo

Dirt Disciple
Thanks Osella and 2manyoranges. The crankset and BB are the same (both Suntour XC) and are compatable.
I will take the cranks off and inspect (there may be some ware). Hopefully just needs a good cleaning and some locktite.
 

Captain Stupido

Senior Retro Guru
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Re:

Usually it's because they have been ridden loose and the square taper within the cranks has become rounded/misshapen. Once that happens they'll always work loose.

When installing bolts need to be done up very tight, and (although opinion varies) I always put a smear of anti-seize on the interface.
 

Graham_hkr

Senior Retro Guru
Re: Re:

Captain Stupido":3hk4ujxx said:
(although opinion varies) I always put a smear of anti-seize on the interface.
Same, a small smear of Copaslip on mine, never had a problem yet!
 
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