Bicycle Mechanics - annoying rattle from crank -help

When I apply pressure - uphill, high gear - the cranks makes a low-volume rattle almost as if the bearings needed grease. But the bike is new and i had them greased and still. It's a Giant Boulder. I can see that the chainring does not run through the front derailleur cleanly. It learches back and forth. At first I thought the chain was rubbing but this also has been checked by the mechanic, who now probably thinks I am hearing things. As I said it is only heard when applying extra pressure. Is is just not a strong bike> I dount that as m old Huffy did not make that noise though I must say the crank did not run flush under pressure. I am about 190 and usually drive in the highest two or three gears - I love the grind. Do I just need a higher quality bike? :confused


man has always wanted to fly

i had a similar noise coming from my crank and it turned out to be that my chain just needed some lube. can't say that is what the case is here but it's always easy to lube a chain

Frequently, cranks will flex under high amounts of load and torque. Are you sure that you are not flexing the crank and rings enough to make them rub slightly on the front derailleur? I work at a Giant dealership and I am familiar with the boulder and while it is a great entry level mountain bike it is by no means the best bike under the sun. The stock crank on those bikes has been pretty good so far but if you are a 190 lb gear grinder I can imagine that the crank is yielding under your pressure a little, just enough to make it rub. Have your mechanic set the front derailleur outer limit a little farther out - not so far as to cause overshifting - but just a little farther than it is now, that should fix your problem. If it doesn't then it is too hard to diagnose by words and I would need to see the bike. By the way have you thought of maybe using a lower gear and "spinning"? It is more efficient and most of the time it is faster not to mention much better for the knees.

-Ryan

I agree with Ryan, more likely flexing under pressure.

If not, could be the cups need greased where they screw in to the frame?

I just had an ultegra left crank arm replaced under warrenty, It cracked aat the splined hole, it started as a normal creak that we've all heard, when I tore the bike down for service I checked everything and could not find the cause of the creak, as I was putting everything back together, I was cleaning the left arm and noticed the crack, I contacted shimano and they replaced it under warrenty. Think about the disaster if the arm would have separated while under load, on a steep climb while clipped into campy record pro fit pedals. The lewels would not have been happy. The strange thing is that the creak was on the down stroke of the right pedal.

Thanks for the responses. This forum is great. Now I have to get busy implementing advise. I will grease the chain and look at the crank arms and try to pinpoint exactly when I hear the noise - it does definitely sound louder on one downstroke more than the other - maybe because one leg is stronger? I hesitate to take it apart as i am a newbie and hate it when I'm grounded for repair. The mechanic has also adjusted the derailleur already more than once and fear the evil eye if I return. On the rack at the shop it's quiet. And yes he did test drive it more than once.
I tend to no think it's rubbing as the sound does not correspond with its lerching to the side when I look down, but I am not ruling it out. Also it sounds like my old undermaintained bike, that had no front derailleur, before I scrapped it. I will follow through on all of the above in order of least hassle. Thank you all.

How many miles on the chain? Chaniring? It could be that the chain and/or chainrings are worn enough that, with the great force you are applying, you are just hearing the sound of the chain on the chain rings.

Check for chain "stretch". Check the leading side of the chainring teeth for wear.

Chain lube would help dampen this sound, but the fix may be either or both a new chain and chainring.

Chain problems as you indicate has the ring of truth. Somehow I think that the chain and the ring are not compatible. I recall once reading that they have to match exactly. The ring is fine as it's about a month old. I tried lubing chain and that does nothing. I honestly feel I need to try another mechanic though the one I am using is the one who sold me the bike. Under warranty I am sure I shouldn't have this problem - in a perfect world. I know it's not the most expensive bike but that shouldn't matter when it's new. However I am prepared to eat crow and go to some other more reputable shop in NYC.
Thanks for the insight.

you might have the mechanic ride alongside you will you test ride the bike and make the noise for him. He may not ride in the same manner you do which could make all the difference in the world. I ride alongside many customers on group rides to check up on problems and make sure things are smooth. Sometimes the mechanic knows too much about how a bike works and subconsciously makes up for the bikes shortcomings in how they ride and shift the bike. It is worth a shot. I know that I have been proved wrong in the past after an alongside testride.

-Ryan

i bought a new chain and the rain got to work on it and after two days of rain it was orange with rust, my bike was making the noises you talk about, and i cleaned the chain and lubed it (not too over the top with the lube/grease),

And your response seems to confirm my suspicion that it's a chain anomaly. Been Busy last few days so haven't has time to re-lube and/or go to the shop.
Will post if there's an interesting turn.