John Redcorn

This started the last few days but not all the time. New rider, new bike 2013 Diamondback outlook entry-model mtb maybe 200-300 miles on it. I ride paved trails, the bike was what fit my budget at the time was a slight step up from a walmart one.

It's only under load, never when coasting, never when being in too low gear and uselessly spinning the pedals. I can feel it in my feet, I can hear it if I tilt an ear toward the ground, I can't tell if it's coming from front or back. When I say every pedal revolution I really really think that's true but not completely sure. When I concentrate on it I'm 90% sure it happens when the left pedal when viewed from the right is at 7 oclock and right pedal at 1 oclock.

Happens any gear front or back.

It doesn't happen at all if I turn the bike upside down and turn pedals by hand, even when braking the wheel some for a little load.

I first thought about the rear derailer, read about how to adjust those and messed with my barrel adjuster through a range of being in 1 gear too high than supposed to be, to being in 1 gear to low, thunk still happens anywhere in that range.

What else should I look at/try?

Retro Grouch 

Check your kickstand's clearance to the left pedal.

no1mad 

Does it happen when you pedal backwards while coasting?

Edit: You might want to be stationary when you try that in case it is the kickstand...

Jeff Wills

Verify that every bolt, nut, and threaded part in the cranks is torqued to spec:
Park Tool Co. » ParkTool Blog » Torque Specifications and Concepts

Northwestrider

It could be as simple as a loose pedal, and that is where I'd start. Possibly your bottom bracket needs adjustment.

StephenH

It could be bad pedals or bottom bearing. I've also had an adjustment nut on the BB that holds it in place work loose, a stop by the bike shop took care of that.

John Redcorn

I've got no kickstand and it doesn't happen pedalling backwards coasting (this is something I thought of and tried) As for making sure everything's torqued right id have to go by feel there, I have a $10 HF beam torque wrench that did ok for hub nuts at like 150 lb/ft on my truck but it's not going to do anything accurate-like. I'll check the pedals too.

Northwestrider

I don't use a torque wrench, I just use a pedal wrench, or you may be lucky and get away using a 15mm open end. Just make sure you turn it in the correct direction. Each pedal tightens or loosens in a different direction.

umazuki

Add another vote for the bottom bracket. Probably needs to be tightened. I suppose it wouldn't be unheard of for it to be defective - check the bike shop you bought it from. They may just replace it.

wphamilton

Is there a thunk when you're standing up pedaling?

BlazingPedals

Another possibility is the front derailleur cage hitting the pedal arm due to the high limit adjustment being off. Or, I suppose, if the cage isn't parallel with the chainring. This can happen even if it's still shifting OK. Don't ask how I know this.

John Redcorn

bahh got stuck at work, mpls dropping packets, going to have to wait until tomorrow to check this stuff out, thanks of the replies you all.

I don't know if it does it standing up or not. Would that indicate something vs. when seated?

It's not the front derailleur hitting pedals, new rider here and spending almost all my time in the middle chainring riding flat trails along a river. (it does it in any of the 3) It's not hitting the chain either, it does sometimes if I twist the shifter too much/not enough so I know that sound.

J.C. Koto

+1, my first thought as well.

I'd start by *carefully* and correctly removing the pedals so as not to strip the threads, clean, inspect and re-lube the threads (and pedal bearings, with some light oil if you can get to them), then *carefully* reinstall the pedals. The reason I wouldn't just tighten the pedals is because if they were initially installed poorly, the threads may have been partially stripped and torquing down will just exacerbate the problem. If you carefully remove the pedals first, the threads will have a tendency to line up right again. Plus, it doesn't hurt to re-grease the threads every once in a while and you have to remove the pedals first to do that

If this doesn't fix it the BB would be a smart thing to check next but that requires special tools so it might be cheaper to have a shop do it.

Homebrew01

Try posting in the mechanics forum if you don't solve it here.

slorollin

Could be a spoke on the rear wheel flexing under load. I had one that only pinged when I was mashing it going uphill.

fietsbob

<wild guess> crank is loose.. bring it by and i'll have a look ..

wphamilton

If there was no thunk standing up you'd look at the saddle, seat post area or frame. This kind of noise can be maddening to track down. I had a cable end sticking out once that I hit every pedal cycle - that really felt stupid when I realized what it was.

Dudelsack 

Hooda thunk it?