Crank sprocket-rear gears alignment

Nitrohorse · #1 08-15-2008, 07:00 AM

I purchased a 4 cycle engine kit which came with the wider three piece crank set. After removing the original one piece bottom bracket and replacing it with the three piece, I noticed that the front crank sprocket is directly in alignment with the outermost gear (7th) on the rear hub. I failed to notice where the original front sprocket lined up with the rear gears prior to removal. My "guess" is that the front sprocket would be aligned somewhere in the middle of the seven rear gears on the back hub, but that's just my guess. Does anyone have a seven speed Schwinn Jaguar that can confirm the alignment of the original one piece front crank sprocket to the relationship of the rear seven gears?
I could kick myself in the butt for not checking this out prior to removel, but I guess it won't the first or last time I do something stupid...
The three piece repalcement crankset is a tapered square drive arrangement and I have it on the BB crank as far as it will go. The only remedy I can see if it has to be moved inward would be to file the crank taper wider until it fits further in on the BB crank?
I'm hoping this isn't necessary, but with my luck, it's most likely the solution.
I enjoy working through this build, but the chinese certianly leave alot to be desired when it comes to tolerances and fit.
Thanks,
Larry

Venice Motor Bikes · #2 08-15-2008, 07:25 AM

Try riding the bike with the sprocket offset the way it is... (you might not even have a problem!)

**Bikeguy Joe** · #3 08-15-2008, 07:36 AM

That's what I was thinking...the derailuer aligns the chain to the rear casstte.

datz510 · #4 08-15-2008, 04:44 PM

If you have problems with the chain jumping off the front chain ring in low gear, pick up a Jump Stop or similar device. Cheap and prevents the chain from coming off the front chain ring.

N-Gear Jump Stop Reviews

You can pick one up for $10 here:
N GEAR JUMP START CHAIN DEFLECTOR at JensonUSA.com

Nitrohorse · #5 08-15-2008, 07:11 PM

I took the bike out of a short ride tonight and I definitely have to move the front pedal sprocket inwards more towards the bike frame. I shift into first gear and the chain sounds like a Rockwell milling machine grinding away on the rear derailer gears. I have to get a little better alignment with the gears and front sprocket if I ever hope to have a chain last.

I did check out the jump stop and I'm going to order one. I also ordered a locking fuel cap today to discourage someone from adding sugar and turning my engine into a cotton candy machine.

Nitrohorse · #6 08-15-2008, 07:15 PM

Quote:

Originally Posted by Bikeguy Joe

That's what I was thinking...the derailuer aligns the chain to the rear casstte.

I agree that the derailer aligns the chain to the gears, but there's an acceptable working range that the derailer was built for and I'm well outside that range. The chain comes off the front sprocket at too much of an angle for the derailer to compensate and see any kind of longevity. At the angle I' currently at, the chain will begin to grind away at the sides of the derailer.

Lightfoot · #7 08-16-2008, 12:04 AM

This article explains chainline adjustment, it deals mostly with high end road bikes but might help.

Bicycle Chainline

sheldonbrown.com is a great resource for working on your own bikes.

Nitrohorse · #8 08-20-2008, 06:46 AM

Well, at this point, the alignment is what it is. I tried to adjust the front pedal sprocket to no avail. The alignment is great for the smaller gears (5-6-7) but is less than favorable for the lower gears.

My next issue is that the chain nearly rubs the rear tire. The easiest fix would be to shim the right side of the rear axle to move the entire tire/hub assembly to the left.
Has anyone had success doing this?