Bottom bracket / crankset movement.

big_southern_jesse

To start with I'll say I've searched the forum, and had a look around the web, but found no real help for this.
I sem to get a lot of flex in the BB/crankset.
When pedalling hard uphill, there is enough movement from side to side, especially on the largest chainring, that the chain grinds on the derailleur guides on each side.
There is no noticeable play in the bottom bracket, certainly it's not loose. Is this just down to the metalwork flexing under load? I'm 16 ish stone and trained for many years as a 2nd row forward when playing rugby and then at my local rowing club! There's a fair amount of force in them there legs!
The bike is a 98/99 Giant 840, kinda entry level groupset. Is this a common problem with cheaper BB or cranksets that could be solved by getting better quality? Or is it a problem that is likely to happen anyway until I smooth out my pedalling and maybe go clipless to help balance the forces?

Anyone else had this problem?

P.S. apologies if there was an equivlent post fairly recently, I didn't find it if there was!

nicklouse

you will just be flexing it.

if it gets to you upgrade to some better cranks.

clanton

One thing to check is that you are not missing any chainring bolts - when I lost mine the first thing I noticed was the rings wobbling and rattling.

supersonic

Could be that: my guess its a square taper BB and flexy crank. Upgrading to external bearing crank or Octalink will reduce it.

big_southern_jesse

Nothing missing, I had a good check around to see if there was any loose play earlier. Guess I just need to get off the big chainring a little earlier and ride a little smoother.

Thanks.

dennisn

I would say that something is loose, out of adjustment, busted, or your frame is broke.
Even the cheapest bikes don't have problems like that unless it's one of the above.

Dennis Noward

supersonic

I have (had) an 97 LX crank and square taper bottom bracket. At 11 stone I could easily flex it causing front mech rub. With an Altus crank, my god!

nicklouse

dennisn wrote:

I would say that something is loose, out of adjustment, busted, or your frame is broke.
Even the cheapest bikes don't have problems like that unless it's one of the above.

Dennis Noward

Nope most cranks flex.

mr mangos

I'm about 12-13 stone and had exactly that problem with cheap suntour cranks and square bb. As super says, going with an external bb will reduce/eliminate it. I went with LX HT2 cranks and the rubbing/flexing disappeared.

ride_whenever

I couldn't flex my 07" HTII cranks on my scott. But on my singlespeed I flex the entire frame!

dennisn

nicklouse wrote:

dennisn wrote:

I would say that something is loose, out of adjustment, busted, or your frame is broke.
Even the cheapest bikes don't have problems like that unless it's one of the above.

Dennis Noward

Nope most cranks flex.

I know they flex but this guy sounds like he has other issues.

Dennis Noward

big_southern_jesse

Thanks to everyone for your help and suggestions.

I've had another really good look around the BB and rechecked everything. There really doesn't seem to be anything loose, busted or broke, and it all runs perfectly the other 98% of the time.

Something I'll live with for now, want to upgrade to clipless pedals and maybe new forks first. I guess with a large frame (23.5) I'm more likely to get a little flex anyway. Gives more leverage to work with.

Thanks again.

Now I've just got to try to get out in this blooming cold! :shock: