Square tapers and BB compatibility question

[mcrocker]

This might make some people go "Durrrrr" but I am prepared for the abuse.

Having built up a Pace F2 I was on the BB/drivetrain and bought some oldish raceface cranks from a now ex-member. I needed a BB to go with them and got sold a nice Dura-ace square taper BB which was narrower than a usual MTB bracket (I think its a 103mm) but the Q-factor was fine in my opinion and so on we went. The non-drive crank however loosened and the taper has obviously been damaged but I don't know if this is because the road square taper is different from the MTB square taper or not. The new cranks (red/pink cromagnon) are needing regular tightening but are not loosening the way they would if the tapers were going. But I am about to put on some T-gear ones and do NOT want to destroy these.

Have I got myself a crap BB and do I need to change it or should I put some more threadlock on it all and relax a bit?

Cheers for advice

Matt

 

[one-eyed_jim]

Some older Dura Ace axles used Campag (ISO) tapers, but the short (103mm) 7410 unit is JIS, and should be interchangeable with a standard JIS mtb bottom bracket (UN72, etc). I've used the 7410 with Ritchey and Sugino JIS cranks without any problems.

Cranks that loosen in use normally haven't been installed to correct torque, and once they start to loosen, damage to the tapers means they'll keep doing it. It's hard to get enough torque with an allen key: they need to be pretty tight. I always grease the tapers. That's controversial, but ungreased tapers require higher installation torque:

http://sheldonbrown.com/brandt/installing-cranks.html

 

[Anthony]

Cranks that loosen in use normally haven't been installed to correct torque, and once they start to loosen, damage to the tapers means they'll keep doing it. It's hard to get enough torque with an allen key: they need to be pretty tight. I always grease the tapers. That's controversial, but ungreased tapers require higher installation torque

I have neither a torque wrench nor a skilled hand, but I always grease the tapers (well anti-sieze actually), and I add torque by using a handlebar over the Allen key. I lay off before I reach the maximum point I could reach though - but still well past were I could get to with just the key. Does that sound ok? I must say I've never had a crank loosen off, but maybe I don't pedal hard enough.

 

[one-eyed_jim]

I have neither a torque wrench nor a skilled hand, but I always grease the tapers (well anti-sieze actually), and I add torque by using a handlebar over the Allen key. I lay off before I reach the maximum point I could reach though - but still well past were I could get to with just the key. Does that sound ok?

Sounds not unlike my own method. I don't own a torque wrench, but I've borrowed one from time to time to "calibrate my arm". Torque recommendations for different cranks can vary quite widely, but the only crank I've had come loose wasn't one that I'd fitted. We must be doing something right.

I must say I've never had a crank loosen off, but maybe I don't pedal hard enough.

Being light certainly helps. I don't have that advantage!

 

[Woz]

Tighten well with a good long allen key (approx 25cm). Do a short ride. Tighten again. Leave it. Works every time.