Bottom bracket works loose every ride...

big_southern_jesse

Morning folks, hoping for some suggestions here...

I ride a SS with a hollow tech bottom bracket. By the end of every ride I find that the cranks have worked loose through the bottom bracket.

Last ride, I had pinched them up nice and tight with the crank bolt, tightened until just before the point where I started to get extra friction against turning the cranks. I then pinched the crank as tight as I could around the shaft and the crank bolt. By the end of 18 miles, I had about 3mm of play in the system, allowing the cranks to wobble all over the place.

Now I know there is a lot of force going through here. There is one climb I can't get all the way up yet, and it's not that I get tired, it's that it's simply too big a gear. I stop when I physically can't push the pedals round. As I'm 90kgs, and relatively fit, I'd guess that's a good 150-200 kgs going through as I pedal.

Anyway, is this a common fault? Is it something that might be cured by upgrading the bottom bracket? Or changing from the hollow tech to a different system? Current BB is a Token ext unit, only £20-something quids worth, but thought it should be up to normal use.

I'm worried that every time it happens, I will be doing damage to the bearings of the bottom bracket.

Any thoughts? Or just use more thread lock and tighten the cranks more?

Cheers,

Jess.

Chunkers1980

What are the cranks?

Sounds odd - shouldn't happen.

njee20

You're talking Hollowtech 2 I assume?

In what plane is the play? Left to right? Or the cranks in relation to each other? If the latter then it could be you've damaged the splines by riding it loose.

big_southern_jesse

The cranks are FSA something or others...

The looseness is the two cranks pulling apart from each other, along the line of the axle through the BB.

Putting it together, one crank with the shaft attached pushes right through the BB, and the other crank slides over this, tightened up against the bearing faces on the outside of the external BB by the crank bolt. It is this tightness that suffers.

cooldad

So it's actually the cranks coming loose and nothing to do with the BB?

big_southern_jesse

Yeah, I guess so. I'm still stuck with the idea that the axle is part of the bottom bracket.

But yes... Cranks

Chunkers1980

which are exactly. rather than something or others. Could be crucial.

benpinnick

Not what you want to here but in my experience FSA cranks are only good for the bin. Every set we've tested on a HT2 type BB do that. You cranks them down and they come loose.

big_southern_jesse

Chunkers1980 wrote:

which are exactly. rather than something or others. Could be crucial.

Pretty certain they are FSA V-drives, but now 4/5 years old.

The Rookie

FSA external BB (not HT2) were never the best anyway, now they've worked loose the spline pattern will be damaged, time to replace I'm afraid.

njee20

Big Southern Jesse wrote:

The cranks are FSA something or others...

The looseness is the two cranks pulling apart from each other, along the line of the axle through the BB.

Putting it together, one crank with the shaft attached pushes right through the BB, and the other crank slides over this, tightened up against the bearing faces on the outside of the external BB by the crank bolt. It is this tightness that suffers.

That bolts needs to be somewhere between hugely and fooking tight. There's every chance you're not doing it tight enough, but now they've come loose your splines are probably mullered.

aidso

Are you greasing them?
I have lost umteen pre-load caps over the last 2 years as a result of censored grease causing the crank arms to rattle loose and eventually fall off.
Also as suggested above, make sure you haven't knackered the threads..

cooldad

You're doing something very wrong, somehow.^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

steelo

You say you weigh 90kgs?
How on earth do you figure that you can put 150-200kgs through the pedals? Even if you stood up you'd only be able to put your full weight onto the pedals, unless you have 50-100kgs in your rucksack!
Or is there some sort of 'increased force due to pedalling muscles' calculation that I'm missing out on?

Ouija

Used to have this happen on the first HT2 Shimanos i had. Turns out it was the way i was tightening the pinch bolts. Cranking one bolt tight and then doing the opposing bolt on the other side meant the two halfs of the pinch prongs weren't meating properly in the center so i wasn't getting even pressure applied all the way round the axle. These days i snug both bolts up and then flip back and forth between the two (see note), doing quarter turns on each one until they are both tight as it's the only way to guarantee both pinch prongs have moved together by the same amount.

Note
Has you tighten one bolt, the other goes loose which can lead you to overcompensate on one side so that both pinch prongs don't move by the same amount. Ignore tightening by pressure/feel and keep to the quarter turn each side, no matter how loose one side or the other feels.

big_southern_jesse

steelo wrote:

You say you weigh 90kgs?
How on earth do you figure that you can put 150-200kgs through the pedals? Even if you stood up you'd only be able to put your full weight onto the pedals, unless you have 50-100kgs in your rucksack!
Or is there some sort of 'increased force due to pedalling muscles' calculation that I'm missing out on?

I do indeed weigh about 90 kgs.. And I can deadlift another 100 or so.. When pedalling uphill, to put more pressure on the pedals, you stand up, engage your core, and use the pull against the handlebars to push against with your legs. On the basis I have bent handlebars before, and occasionally really fear for these ones, I think it's reasonable to assume the force I add simply beyond gravity acting on my body equates to at least 60 kgs... Fair enough? Maybe 110 extra is a bit much, but a short sharp climb is often attack at speed, use the run up to get most of the way up, and then 5-10 reps over the top. I can easily put that much force down for that many reps.

steviecapt

i have an fsa crankset and bottom bracket on my boardman, the problem ive found is that the preload bolt on the left hand crank arm ,comes loose, and after a few times it will never hold again, so before wasting money on a new crankset, just buy a new left arm crank bolt, make sure when you tighten it you dont put too much load on the bearings, as this is why when halfords staff do them up, they prematurely wear the bottom bracket, and make sure there is threadlock on the bolt, ive had my boardman over two years, and its done well over 2500 miles, and its still on the original cranks and bottom bracket, theres nothing wrong with fsa, its the way their fitted that matters

The Rookie

Big Southern Jesse wrote:

steelo wrote:

You say you weigh 90kgs?
How on earth do you figure that you can put 150-200kgs through the pedals? Even if you stood up you'd only be able to put your full weight onto the pedals, unless you have 50-100kgs in your rucksack!
Or is there some sort of 'increased force due to pedalling muscles' calculation that I'm missing out on?

I do indeed weigh about 90 kgs.. And I can deadlift another 100 or so.. When pedalling uphill, to put more pressure on the pedals, you stand up, engage your core, and use the pull against the handlebars to push against with your legs. On the basis I have bent handlebars before, and occasionally really fear for these ones, I think it's reasonable to assume the force I add simply beyond gravity acting on my body equates to at least 60 kgs... Fair enough? Maybe 110 extra is a bit much, but a short sharp climb is often attack at speed, use the run up to get most of the way up, and then 5-10 reps over the top. I can easily put that much force down for that many reps.

Your pulling up the bars is not inline with your pushing down on the pedals and would just twist you over the bars, you won't be adding anywhere near 60kg by doing that, probably 20-30 for a brief period at most, most of that is used to offset the tilting force of the bike by standing on one pedal anyway.

Monty Dog

Cranks have been ridden loose which has distorted the splines - time to replace the cranks.