Bicycle Mechanics - newbie problem

I a Trek 800 sport and just recently it has started to give a popping sound when I am peddaling hard (ie climbing a hill or pulling a trailer) it sounds like it is coming from the ?crankcase? anybody know what the problem is? I have "frankinsteined" lots of old bikes and I am pretty good at tuning up, but this is my first new bike:o so I am a bit nervous about it. thanks for any help.

Sounds like the crank bearing/axle unit (called the "bottom bracket") is not fully snug in the frame. Since your bike is new, you can expect your bike shop to handle that for you.

Fixing it wouldn't be too hard though, if you wanted to tackle it yourself. You would remove the crank bolts, then use a crank extractor to take the cranks off the spindle, back off the side of the bottom bracket that doesn't have a flange, then snug the flanged side very firmly against the frame, snug the other side fairly firmly, and reinstall your cranks.

For most of today's bottom brackets, a tool like this one is used: http://www.parktool.com/tools/BBT_2BIG.shtml

Welcome to BikeForums, by the way! :)

I guess I should add that the instructions I gave above are based on the assumption that the bottom bracket is a cartridge style. With entry-level bikes, there are some that still use a conventional cup-&-cone bearing arrangement, although some of them even use the cartridge-style tool like I linked to.

If the non-driveside bearing cup has a notched lockring up against the frame, then it's most likely one of these fully-adjustable types, even if a cartridge tool happens to fit... I worked on one of these for a co-worker today, matter of fact. You may already be up to speed on that type of bottom bracket, but here's Park Tool's rundown on it, just for completeness:

http://www.parktool.com/repair_help/FAQadjbb.shtml

The cause of the problem would still be the same, however... the driveside cup needs to be very firmly snugged against the frame.

The sound may be loose spokes as well.

If you're very close to Spokane, bring it over and I'll look at and
( probably) fix it for you!!!!!

Ride Quieter
Pat

Yeah it could be a spoke but it should be possible to work out whether the noise is coming from a wheel or the BB area. (Preferably before you ride into a tree) Another thing to check is that one of the cranks arms hasn't got some slight play on the axle shaft. Try checking/tightening both crank nuts/bolts and see if the noise goes away.

If it is a loose crank arm you need to see to it soon before the arm hole gets worn and ovaled You'll have to chuck the crank then.

It could also depend on the quality of the BB cartridge assuming one is fitted. I am not familiar with the spec of this bike, but I have some of the new cartridges I've used tend to make a bit of noise until they wear in, quite possibly more common with the lower-quality ones. I had a mid-level Shimano BB that did this within the first 200km. It wore in after 1,000km and has been silent since.