ph0rk

Ok, so this is probably the worst sort of thing to diagnose via text, but bear with me.

Bike is a Trek Crossrip elite. Had a few hundred hard gravel miles, now is a relaxed commuter. Chain is new, chainrings and cassette are original (FSA and an SRAM 9-speed). Wheels are not original (WTB SX19's on x7 hubs), but the cassette is on nice and tight and the skewers

Pedals are tight, no play in BB. Headset is adjusted well, bars, levers, and interrupter levers are tight. Seat collar is tight (possibly the seatpost needs grease, it is on my list).

When I apply power, most usually from a stop, and more typically the left pedal but also at times the right (I usually go through a half spin with my right leg and then stand on my left), there is a slight "clunk" sound - as if something mechanical slips. Sort of like the sound you'd expect if something that spins is not tight (cassette lockring, crank arm bolt, etc) As far as I can tell, it all is, and I've had another pair of eyes go over and check bolts. There is a rack on the bike, and it could be some weirdness there if the seat stays are flexing, but I don't really think the seat stays are made to flex much on this frame.

Once I'm moving and applying only moderate power I don't hear it - it is only a stand and climb or grab the bars and mash sort of thing, and not on every stroke or even every fifth stroke.

What might cause something like this? Does the BB need to be lubed?

fietsbob

Your right , Find a shop to see it. which cannot be done ,Here.

<guess> Freehub Pawls may just be engaging Late, because the grease is cold its delayed a little.

Andrew R Stewart 

It is possible for a bearing or press fit to feel tight with hand pressure but show "looseness" under the far greater pressures of pedaling. Andy.

ph0rk

Yeah, this was what I was worried about. I followed some of the steps from Sheldon Brown's website, and I think it is the BB. Following these steps:

I can feel a pulse or ever so slight movement of the crank arm when I align it with the seat tube and squeeze hard, that alternates from side to side. Crud.

Oh well, an excuse to buy a few more tools is never a bad thing!

Plimogz

New chain skipping on the most worn cassette sprocket when under heavy load (i.e standing start after a stop, mashing out of saddle, etc.) ?

bradtx

This is my guess also. If you still have the old chain, install it and see if the problem clears. If anything the diagnosing starts at the least expensive items.

Brad

Shimagnolo

I've had clunks from:
- Cheap plastic platform pedals. Wear had ovaled out the plastic around the bearing, letting the bearing move around.
- New chain skipping on worn cassette.
- Loose cassette lockring.

CafeVelo

Cleats maybe? It could also be somewhere else on the bike but related to torque from the pedals. A good mechanic could tell you what it's not at least.

ph0rk

So, the noise existed before the chain replacement. Cassette lockring is tight (rechecked). Pedals are shimano a-530's, used with sneakers (not clipless, and on the platform side obviously). Cassette isn't looking terribly worn (about what you'd expect in 1500 miles with regular cleaning), and the noise sounds like something slipping, maybe, but I don't feel the pedal or chain slip - the noise is more subtle than that, too.

I can make it make something like the noise if I squeeze the crank against the seattube then spin the cranks and squeeze the other against the seattube. I don't have the tools to pull apart the BB, so I'm going to visit my LBS today or tomorrow. I don't mind throwing a few dollars at it, I guess. I hate undiagnosed noises.

I'm sure Trek just put the cheapest BB they could find in this bike, and it probably wasn't properly tightened, to boot.

CafeVelo

Id start with a regrease and tightening of the bottom bracket. IIRC it's threaded on that bike. I have to loctite the cups of external bottom brackets or they walk out over time, but a lot of people have no trouble.

rm -rf

It's a "clunk", not a click, or a creak?

Are those FSA cranks, with the two bolts on the non-drive arm? I used to get a clicking noise on my old bike. I had to remove the crank arm, wipe the splines clean, grease the splines, and reassemble.

I used teflon tape on the Mega Exo external bottom bracket threads.

On my new bike, I was sure that the bottom bracket PF30 was creaking. It was intermittent, usually happening when standing or starting off fast. But it's the rear skewer. I had to clean and lube the skewer pivots, and clamp it a little tighter. That fixed it. (But it comes back occasionally if I'm not careful about clamping it.)

ph0rk

That looks like it took care of it - full regrease and retighten.

No, one bolt per arm.

I have actually tried a second wheelset in this bike(!), pretty certain that wasn't it. I could localize the 'pulse' with my feet, it alternated sides of the BB - hard to put into words. Post grease and tighten was a pretty big difference - the bike felt stiffer and more responsive when standing and mashing in a way I didn't even notice I was missing.

I figure the grease and retighten should do for a while, with any luck long enough for me to be antsy to try a different groupset (ditching the FSA components in the process - Tiagra 4700 most likely). AFAIK I'd need a new BB as the current BB is square taper.

Monkey Face

I had something like this happen once and it was diagnosed as being something to do with the rear hub. I wasn't mechanically minded at the time, so I left it to the mechanic and didn't pay much attention to the details. My advice is take it to a bike mechanic... there's no point driving yourself nuts over it.

pdlamb

I've had it from a crank that wasn't tightened quite enough. Make sure they're torqued correctly (that is, really tight!).