Hello all,

I ride a singlespeed freewheel vintage fuji convert and I recently upgraded my whole drivetrain. When I tried turning the cranks, the chain started wobbling around a bunch and making an odd sort of rattling noise. What's wrong with it?

Let me guess.

Did you properly tension the chain?

If so that may be your problem, since single speed chain drives must be "tensioned" so there's some slack at all times. Poperly set there'll be roughly 1/4" vertical play in the center of the slack loop. Note also that chainrings and sprockets are usually slightly eccentric (like bike riders) so the amount of slack will vary. You want to be sure there's still some vestigial slack at the tightest point tin the cycle.

Yes I have tried that. The weird thing is, (I don't know how this is possible) but the top part of the chain is tighter than the bottom... again, I have no idea how this is possible. Any other ideas?

Not possible unless you push the crank or move the wheel. While riding the upper loop will always have the tension because hat's how it pulls the sprocket around.

If you hold a fixed wheel bike stationary, you can transfer tension between the upper and lower loop by pushing the pedal back and forth. Usually the pedal will have about 1/4-1/2" of this "backlash" movement. On a freewheel bike it's impossible to tension the lower loop because the freewheel will always feed chain into it.

Is your chain line correct, that is, are the chainwheel and cog correctly aligned with each other and with the chain? Do they rotate without wobble or excess eccentricity on their own? Is the chain the correct width for the other components and closed correctly without any tight links? Is the chainwheel correctly and securely attached to the crank, and the cog and freewheel to the rear hub? Bottom bracket and freewheel turning freely without excess play or binding?

In troubleshooting one generally looks first at the last thing changed. Since you have upgraded the whole system you should probably take a step back end ensure that each individual component is suitable for the system and correctly installed.