Bicycle Mechanics - torqued off

i get a new specialized 415 for my birthday, but it pedals like crap, it's noisy, the crank spins 1/2 turn at most when flicked with the wrist, so it goes back to the bikeshop, mechanic adjusts the brakes, loosens the crank a little, does some minor alignment of the sprockets, wife brings it to me, same thing, on further examination i flipped it upside down and turned the cranks in the freewheel direction, the chain gets real tight top and bottom then 1/3 turn gets real loose, so it's going back today again, is the sprocket warped or the whole bb hosed, it feels like pedaling an xmart bike.

First off, you need to take the bike to the shop yourself - not have your wife do it. She likely does not understand the situation as well as you do and since the mechanic needs to know what is going on you need to explain it to him. Second, all chainrings have a little offset to them. Even with all the technology the world possesses today manufacturers still cannot drill the hole exactly in the middle of the chainwheel. This is going to cause a tight spot and a loose spot in the pedal revolution. A little is normal and I have only had a few extreme cases where the chainwheel had to be replaced. Since it is a new bike if the chainwheel is bad the shop will replace it free o' charge do dont worry too much about it. The reason your bottom bracket doesn't spin freely is because the chain is probably too tight and the tension on the freewheel bearings is adding extra friction in the drivetrain. Try letting that chain tensioner out a little bit and check with the shop about your chainwheel. Good luck.

-Ryan

"Even with all the technology the world possesses today manufacturers still cannot drill the hole exactly in the middle of the chainwheel"


What is this about?

i've been working 13+ hour days continually and have no time to visit a bike shop thats closed anyway when i get off, i've talked to the guy and i'm trading it for a redline thats much smoother but not as good looking. i fail to see why a $300 bike should pedal rougher and more like sandpaper than an $80 bike. The chain is plenty loose-tight-loose-tight-loose-tight(pedaling), that was one of the adjustments when we brought it back the next day. this is a black eye for specialized in my book and not a good mark for the lbs.

Try shifting to the small-small chainring/cog combo and see if it still does the "tight/loose" thingy. What combo are you in when it acts up? I'm thinking that maybe your chain is too short.

a specialized 415 is a bmx bike, i tried shifting but the levers were gone (just kidding).

BMX????.....oops! Possibly the chain is stretched in one area giving you that tight/loose syndrome as you pedal.

yeah, but the bike is like two days old, more likely an out of round or warped sprocket or BB. too bad cause i always liked specialized. everythings made in china now which makes me really question the quality difference on name brands and other brands as far as frame components go

I think they make them in Tiawan. The loose tight thing does happen on bmx bikes sometimes. It really is not Specialized fault (I have seen profile cranks and ring do this and they cost about what that whole bike does. It really does fall back on the dealer, they should set the bike up correctly when new and if it has a problem then fix it. If they don't catch it (Happens, I have worked in a shop for 10 years) then, when you bring it back they need to fix it or other wise make you happy Which it sounds like they tried to do by getting you another bike.
Mistakes happen everywhere, In my previous field I have seen a brand new $2000 pump fail and spew its innards all thru a $10000 transmision. Now that is a warranty claim.
Remember to your one experience was bad, Specialized builds thousands of bikes. There success rate is far higher than the average persons ability to stick the correct key in their own front door on the first try.

The chainring is bent, causeing the cahin to tighten up when it reaches the bent section. Being a new bike, I'd have the chainring replaced. This can happen in shipping or even transporting the bike from the shop to the your house.

Originally posted by sunsetnkc
"Even with all the technology the world possesses today manufacturers still cannot drill the hole exactly in the middle of the chainwheel"


What is this about?

I am not talking like it is massively out of center but instead we are talking about mere millimeters or sometimes less. It is always slightly off causing the chainring to have a place in its revolution where it causes a tight spot on the drivetrain. Here is what Mr. Brown says about the situation.

"If the chain is too tight, the drive train will bind, perhaps only at one angle of the pedals (chainwheels are not usually perfectly concentric). It should be tight as it can be without binding. If the chain is too loose, it can fall off, usually at the most inconvenient possible time." -Sheldon Brown


-Ryan

it's been traded in on a redline double x se, i'm very happy with it, not as good looking as the specialized but more solid, sealed bb, 48 spoke wheels, both have three piece cranks but the redline doesn't make creaking sound, the bike shop did good, i think they need to open the bb one the old one and regrease and adjust and put on a new chainwheel before they sell it.

I suspect that your chainring isn't perfectly concentric with the bottom bracket. There are two ways to address this problem.

1. Quick and dirty. Adjust your chain tension by making minute front-to-back adjustments of your rear wheel in the drop outs. After each adjustment, spin your cranks by hand. If they always stop in the same place, your chain is too tight. If several spins of the crank results in different stopping places, check to see if your chain is too loose. Work at it until you find the "sweet spot."

2. Harder to do, but more precise if you have a separate chainring spider. Start with your chain on the tight side. Now loosen your chainring bolts just a touch- you want the chainring to be able to move under pressure, but not slide all over the place. Now spin your crank a few times. The chain should pull the chainring in the tight areas and center it on your crank spider.