[schwinnstr8]

Okay..here is the situation. I bought profile cranks for my straight 8 and installed them. My problem is...when i screw in the bolts that hold in the arms to the spindle; if i tighten them too much the arms wont spin, but if i don't tighten them enough they come loose while i ride. I tried to use lock-tight but that also didn't work. Has anyone ran into this problem??? Help!!! i want it ready for big bear this weekend. Thanks in advance!

 

[s1ngletrack]

Sounds like you are missing the internal spacer on your BB

 

[WestCoastHucker]

they are supposed to be snug, but not so much they sideload the bearings. i find it strange you have problems with them loosening up on you. i could run mine with no crankbolts and they wouldn't come loose. that is a serious pressfitting going on there...

 

[s1ngletrack]

What happens is that the bearings want (if bearings can actually want anything) to collapse into your BB shell because there is not a spacer between them and the horizontal load on them is too great - this causes them to bind when you tighten them enough to encounter resistance on the spindle bolt.

 

[profro]

I think your problem might be that the spacers outside of the bearings are too big. What happens is that when you tighten the arms down they press against the bearings instead of the inside race (smaller) of the cartridge. Make sure that you spacers, or at least the inside most spacer, are the same diameter as the inside bearing race. Most spacers provided are too big.

 

[SKYWAYBUZZ]

Those first spacers outside the cups sometimes need filed down a bit. They are slightly too big in diameter and rub into the cups. Slows the spin of the cranks.

 

[zane]

The spacer inside the BB is either MISSING or TOO SMALL. If it's too narrow put one of the super-thin crank arm spacers in the BB with the stock spacer. I had to do this on a couple of my BMX bikes. The bolts that hold on the arms should be as tight as possible, the bearing tension has nothing to do with the side bolts if the inside spacer is correct.

Edit- an easy way to tell if your BB spacer is too narrow is to install the BB correctly, making sure the cups are tight. Then, put your finger in the hole where the spindle would go and see if the spacer wiggles around. If the spacer can move around, it's too narrow. It should be held between the bearings snugly (eg.- unable to wiggle around) when the cups are tight into the frame.

 

[buildyourown]

What happens is that the bearings want (if bearings can actually want anything) to collapse into your BB shell because there is not a spacer between them and the horizontal load on them is too great - this causes them to bind when you tighten them enough to encounter resistance on the spindle bolt.

There should be a spacer in there. If you bought your cranks new, there should be 2 spacers. One for 68mm and one for 73mm. Make sure you are using the right one. When I bought a set used, the yahoo who had them before put one of the small external spacers in between the cartridge bearing and the cup. Same thing happened, when I tightened down on them, they wouldn't spin.

If they are set up right, you should be able to crank on the bolts without them getting hard to turn.

As for press fit, my older set just slide on and off without a problem.

 

[schwinnstr8]

Thanks for all the advice! Im going to work on it right now. Thanks again!

 

[BMXman]

The spacer inside the BB is either MISSING or TOO SMALL. If it's too narrow put one of the super-thin crank arm spacers in the BB with the stock spacer. I had to do this on a couple of my BMX bikes. The bolts that hold on the arms should be as tight as possible, the bearing tension has nothing to do with the side bolts if the inside spacer is correct.

Edit- an easy way to tell if your BB spacer is too narrow is to install the BB correctly, making sure the cups are tight. Then, put your finger in the hole where the spindle would go and see if the spacer wiggles around. If the spacer can move around, it's too narrow. It should be held between the bearings snugly (eg.- unable to wiggle around) when the cups are tight into the frame.

ah the correct answer

 

[SKYWAYBUZZ]

Ya but when you add a chain guide ISCG mount flange between the cup and frame those 68 or 73mm. spacers will need a additional spacer.