Bicycle Mechanics - Loud popping sound coming from crank?

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Bodeco
09-19-05, 05:08 PM
Hi all, I have a really disturbing popping sound coming from my crank (or so it appears). I would love to drop my bike off at my LBS, but they are days behind and I hate to be without my bike for that long. I am hoping to get some ideas from you all on how to fix this.

When I am sitting and pedaling on level ground, the crank is pretty quiet. However, when I am pedaling hard or going up a hill, this terrible popping sound starts and it feels like it's coming from the crank. At first, it only happened when the right pedal was about 2:00 as you face the bikes right side. Now it seems to be happening on both sides, more often, and much louder. My friends and I did a 31 mile greenway/street ride yesterday and it got progressively worse as the day went on. At the end, it was downright embarrassing it was so loud. Nothing seems loose, and the bike doesn't seem to be malfunctioning at all. Shifting is smooth.

Any ideas? I haven't really tinkered with it closely, but I plan to tonight. Will be glad to post pictures or clarify anything.

General info:
Bike: Trek 4500 (hardtail mtb)
Me: 6'0'', 260lbs <- likely a huge factor

Thanks for any ideas you may have.

HillRider
09-19-05, 05:18 PM
Again, there are three possible sources:

1. The bottom bracket cups are too loose or not properly lubricated.

2. The crank arms are loose on the spindle. (If this is it, get it fixed fast!)

3. The pedals are loose in the crank arms or the pedal bearings are defective.
puregsr
09-19-05, 09:35 PM
I have the same exact problem ... right after I rode into the sand.
I cleaned and lubed the chain completely, greased the hubs of both wheels, the bottom bracket (new bearing balls), and the pedals. The grinding noise is still there.
=( I think it's the chain.

mtbikerinpa
09-20-05, 09:03 PM
That sound, at least in my experience is almost always your crankarm/spindle bolt. BEFORE RIDING FARTHER, tighen it. The wear that takes place when the bolts are loose can be fatal to the arm if let go too long. The best way to know you are tightening it propperly is to invest in a Torque-wrench. 35-45 ft-lbs is the typical range.