Bicycle Mechanics - Knocking noise from BB
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05-19-03, 05:31 AM
Here's an odd one (at least for me). The bike in question is my '03 K2 Mach 2.0 with just over 1000 miles on it. The crankset is a TruVativ Elita triple.
While riding this past weekend I would notice a prounounced knocking noise while riding. It didn't happen every revolution of the cranks but would make the noise when under a heavier than normal load such as when climbing or hammering on the big ring on the flats.
The knocking sound only seemed to happen when the right crank was between the 12 and 3 o'clock positions. After we finished the ride I checked to see if either of the crankarms were loose and neither appeared to be.
What really makes this odd is I heard the noise on rides on Saturday and yesterday but did not hear the noise this morning on my commute to work.
Anyone ever have to deal with a knocking BB before?
If the crankarms aren't loose, then I'd say bad bearing.
Here's what I do when I have a BB that knocks..
A) Check the crankarms..if that isn't it I go to B
B) Make sure the BB isn't loose..if that isn't it, I go to C
C) New BB
One other thing, my friend was having BB problems, and we tried A, B, and C. It turned out to be a loose rear quick release, it made me feel stupid!!
05-19-03, 08:04 AM
well, i was going to post a simliar question...
my BB creaks REALLY loud under heaver load (i scared a pedestrian today when i got out of the saddle to sprint away from a light).
so i'm pretty sure i need a new BB. the question is: how bad is it to ride a few hundred km before i replace it?
and if it completely fails could it damage the frame or cranks or anything?
lastly, i know how to pull the cranks (i've replace chainrings quite often). how much more work is it to replace the BB? and do you need any special tools (other than a crank-puller which i already have)?
05-19-03, 05:08 PM
Thanks for the replies folks. I sent an email to TruVativ explaining the problem and they suggested I pull the crankarms and spin the bottom bracket with my hand to see if is smooth or not.
Armed with this information I rushed home on the afternoon commute so I could take the bike to the LBS. I knew I was in trouble when I was explaining the problem to the owner of the LBS and he gave me that RCA Dog look :( He wanted me to leave the bike with him until Friday. I told him thanks but no thanks. I'm going to call a shop in a near by town and see if I can schedule an appt to have the bike looked at as soon as I bring it in.
He did suggest I remove the chainring bolts one at a time, regrease them and reinstall them. He said sometimes folks confuse noisy chainring bolts for bottom bracket problems. Althogh I think he's nuts I'm heading out to the garage and give his suggestion a try.
I'll post an update after I get a 2nd opinion.
05-19-03, 05:20 PM
Couldn't hurt to grease the chainring bolts, but I doubt that is it. Really sounds like the BB. Have you tried rocking the cranks? Line an arm up with a frame tube and squeeze like a hand exerciser then pull back with your other hand. Also if you drop the chain onto the BB shell you can get a better feel for if the BB is crunchy.
You're only about 8 hours away, drive up and I will take a look at it.
05-21-03, 03:50 PM
Just thought I'd post a quick followup. I took the bike to a shop where I trust the mechanic and he told me that the bottom bracket was fine and adjusted properly but that both crankarms were loose :(.
$5.00 later I'm out the door with no more knocking. He did say that the bottom bracket was a pretty low-end bottom bracket and I'm going to let him replace it with a better one, probably Ultegra, after I get the Lemond.
Hehe, cranks arms once again..I think it's safe to say 9 times out of 10 knocking is because of the arms being loose..I've only had one instance where the BB was a problem.
Well fubar in my case it was both loose crankarms AND a bad BB. I knew I should have checked it sooner......oh well live and learn. At least I didn't have to pay labor this time. :D
01-27-12, 11:24 PM
I prefer to search and resurrect an old thread than start a new one for the same thing....
I have this problem now, and Ive brought it to my LBS 3 times, and the knocking keeps coming back. Right now it's so bad, it knocks almost every time I pedal.
I thought it might have been a ball bearing, I highly doubt it's a crank arm in my case as I know that the mechanic has pulled apart the whole drive train and I've seen how careful he is to tighten things properly.
If it is a bad BB I am a bit disappointed that this old and obviously experienced mechanic hasn't offered to check or change them.
I even mentioned BB's as even in my limited knowledge, my feet "told" me I was feeling a bad BB.
He cited that I am heavy and that I ride very hard and seemed to have the attitude that he has done all he could.
I think I will go in and ask that the BB's be checked/replaced.
I want this knocking between feet gone!!!
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