Bicycle Mechanics - Roughness

I have a single speed bicycle I'm working on at the moment. It works fine under light pedaling and coasting, but becomes rough to pedal under load. I get a general "vibrating" kind of feeling in the bicycle when pedaling under load, as if something isn't meshing quite smoothly.

The problem began in earnest when I changed to a new crank set and put on a new chain. I went through and made sure there were no tight links. I opened the rear hub up today and found no problems there-- it appears brand new and has plenty of grease.

Would a wacky chainline cause this kind of a reaction or would that run rough all of the time? The roughness under load is driving me nuts. It runs fine on a flat or downhill, but the minute I have to tackle a hill and I apply force to it I get the problem.

overly tight chain and a tight spot on the chain ring?

It would take an obviously out of whack chain line to cause that feeling so it probably isn't that.

Worn BB?

Some interesting ideas here-- I'll have a look at the chainring I put on. It's brand new, but I wonder if it could have been mis-manufactured.

I've got a different chain on order too, just in case it's a chain-related issue.

I'll also take a look at the bottom bracket again. I've taken it apart a couple times, but found no obvious wear or damage taking place there. I will say the old crank set and the new crank set as slightly different in a couple of regards, but besides the spacing appear the same (though I used spacers to try and set the new one up like the old one and the chain line looked okay).

The next step I'll try is to put the old cranks back on and test it again to see if anything triggers the problem. After that I'll try a different chainring.

Any other advice from the locals here is much appreciated.

Certainly could be a funky chainline.

Also, the fg crowd is well-aware that cogs/rings/chains sometimes take a bit to wear in together. With a spring-loaded rear derailleur or tensioner, this grittiness seems to be soaked up by the spring. Without the spring, you feel every little bump down there.

jim

worn bb--- clunky freewheel or broken axel--- bent, axel, wrong size bearings in either bb or axel--- freewheel shifts under load--- back to my coffee

it sound like a broken (crack) axle to me , when you pit tension on it by riding up hill or hard pedaling the crack spread and gives you your problems. when you ride on level ground or easy on the pedals it goes away . you will have to remove the axle and flex it to see it, or wait until it break.

Hmm I suppose that's possible, though I don't know what I would have done to damage the axle. It's a solid axle and not a quick release and I don't beat on the thing. I'll have another look at it though. How hard is it to bend or crack a solid axle? I've babied this thing since I got it a few weeks ago.

loose races--- sometime a flex will push something to the stays-- a solid axle does bend--- and if the races are sloppy or looose-- they will creep into the bearings and score the hub racesf etc. . . check one item at a tiime
bb; front rings, tension, line, rear wheel--- assemblys .......chain combatability--- ramped teeth?