Bottom bracket overhaul

[mjmcguire]

Good evening, Recently my left crank arm bolt has taken to working itself loose after only five miles of riding. Should I use Locktite to keep it tight or could there be a wear problem in the bottom bracket. The bottom bracket has gone 18,000 miles. Thanks, Mike

[Bill]

Hi Mike,

1st welcome to the forum . 18,000 miles wow, good health from that. I have always tried to stay away from locktite on important parts such as that. If you have a picture of the crank with the bolt it would help. If you tighten back up with the proper tool does it come back loose? If it does, after that many miles maybe you could invest in a new Bottom Bracket assembly? I'm just guessing in the dark.

[Joe_W]

Hard to say what is wrong. From the context I'd say it is a tapered square type bottom bracket. The described problems could come from a worn crank arm or bottom bracket axle (well, the tapered part). Is there any play between crank arm and bottom bracket? Do the square hole in the crank arm and the tapered square spindle still look ok? If no, you will have to replace that part. You could be able to get a used crank arm for not much money from the local bike shop, might be an option. I also don't think locktite will work in the described situation...

[mjmcguire]

Thanks for the reply Bill. I wondered about Loktite as being too "permanent". I tighten the crank bolt with a #8 allen wrench and snug it up pretty well. At the end of a ride yesterday, it wobbled loose and then had to be tightened again about every 5 miles and after 2 miles, going up a steep hill. The problem may mean a trip to the LBS, but I will do some more inspecting before taking it in for "I think you need a new. . ." Mike

(12-30-2009, 09:50 AM)Bill Wrote:  Hi Mike,

1st welcome to the forum . 18,000 miles wow, good health from that. I have always tried to stay away from locktite on important parts such as that. If you have a picture of the crank with the bolt it would help. If you tighten back up with the proper tool does it come back loose? If it does, after that many miles maybe you could invest in a new Bottom Bracket assembly? I'm just guessing in the dark.

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TYhanks Joe. I'll do some more investigating. Since I have done nothing with the bottom bracket and crank arms since I had the bike put together, it could be time for a replacement of something or another.

Mike

(12-30-2009, 11:55 AM)Joe_W Wrote:  Hard to say what is wrong. From the context I'd say it is a tapered square type bottom bracket. The described problems could come from a worn crank arm or bottom bracket axle (well, the tapered part). Is there any play between crank arm and bottom bracket? Do the square hole in the crank arm and the tapered square spindle still look ok? If no, you will have to replace that part. You could be able to get a used crank arm for not much money from the local bike shop, might be an option. I also don't think locktite will work in the described situation...

[bighornz]

18,000 is pretty good out of BB. Work it out per mile and you end up with a pretty good economy case for buying a new one.

[mjmcguire]

(02-26-2010, 11:35 PM)bighornz Wrote:  18,000 is pretty good out of BB. Work it out per mile and you end up with a pretty good economy case for buying a new one.

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Thanks for the note. I thought I would wear out before the bottom bracket. Now I'll try to out-last the headset! Mike

[jr14]

I'll go along with everyone else and say 18,000 miles from a bottom bracket is above and beyond what one would expect.

I concur with the worn axle. Small price to to pay after 18K.

[Bill]

I only have one thing to say, Where do I buy some of those parts? lol

[DaveM]

18K is a lot on a BB. But loosening crank bolts are almost always caused by a worn crank arm and not by the BB spindle. The spindle is steel and the crank is (usually) aluminum.

If the crank arm keeps getting loose after the bolt has been tightened correctly, you'll probably need a new crank. This assumes that you don't have stripped threads on the bolt or BB spindle.

[JonB]

Another possible cause is an unwell crank bolt.

You said you would just have to tighten it and it would be fine, but work loose later until it's tightened up again, which sounds like the crank bolt is loose rather than the crank. If the crank/spindle was worn out you'd have play even when it was tight.

Try getting a new crank bolt (should be pretty cheap, and even if it doesn't work it's always good to have a spare), put a small amount of copper grease on and tighten it. If it works itself loose again continually then I think the bottom bracket spindle threads may be unwell.

[buzz]

I had this problem a while back. One thing to do when you tighten the crank bolt, see how much space is between the crank arm and the rest of the bottom bracket assembly and compare to the other side. The mechanic showed me and there was a noticeable difference in the spacing and wound up getting a new left crank arm and have not had any problems since.

[mjmcguire]

(03-01-2010, 08:46 PM)buzz Wrote:  I had this problem a while back. One thing to do when you tighten the crank bolt, see how much space is between the crank arm and the rest of the bottom bracket assembly and compare to the other side. The mechanic showed me and there was a noticeable difference in the spacing and wound up getting a new left crank arm and have not had any problems since.

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Thanks Buzz. I'll check out your suggestion. A bottom bracket is kind of like subflooring - not very sexy or a part that is worth showing off but important for other parts to do their job! Mike