Clank every pedal rotation?

[toontra]

Trying to narrow down an annoyance.  Once every pedal rotation there is quite a loud clanking noise, BUT only when in the small ring (compact 50-34).  Louder the heavier the load.

It's a BBright pressfit bottom bracket (Cervelo S2) with Sram Force 22 crankset.  As it's synced to the pedal rotation I assume that it's the bottom bracket bearings or the crankset, but can't understand why it only happens in the small ring (irrespective of load on either ring).

Nothing as simple as components hitting each other unfortunately

Any suggestions much appreciated.

[hellymedic]

Loose chainring bolts?

[nuttycyclist]

I had that on a traditional square taper BB, and nipping the crank bolts up sorted it.

[toontra]

Thanks both.  Have taken the crankset off & tightened up the chainring bolts.  Will test tomorrow!

[Canardly]

Same issue ta.

[nuttycyclist]

It's been mentioned in other threads recently, and I was embarassed to have forgotten it.    Pedal bearings?

Other items that have cropped in the recent threads are zips knocking on the top tube/cable end clipping the chain/etc

[andyoxon]

Chain catcher outta whack  - I've had this (in small ring).  I've also had loose chainring bolts, but that was creaking - under power.

[Gattopardo]

Had play/slight in a rear cog that caused a clank.

[DaveReading]

Had play/slight in a rear cog that caused a clank.

But not one clank for every pedal rotation, presumably?

[toontra]

As an update - tightening all bolts on the chainset (including chainring bolts) hasn't improved matters.
The clunk is every time the left crank is at about 2 o'clock - I. e.  most applied force, but only when the chain is on the small ring. The clunk is louder the greater the power being exerted.

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[SpaceBadger]

The small ring aspect might be a red herring, reflecting somewhat different cadence or power between the rings. Pedal bearings (already mentioned) is a good shout, play in the rear hub. At a push, perhaps a creaky QR. The clunk points to BB bearings, though. You’re going to have to replace them at some point, so won’t be a wasted investment if swapping bearings doesn’t fix it.

[toontra]

The small ring aspect might be a red herring, reflecting somewhat different cadence or power between the rings. Pedal bearings (already mentioned) is a good shout, play in the rear hub. At a push, perhaps a creaky QR. The clunk points to BB bearings, though. You’re going to have to replace them at some point, so won’t be a wasted investment if swapping bearings doesn’t fix it.

Indeed, that's the next step. Being a pressfit that means a visit to the lbs - not something I have the tools for.

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[robgul]

The small ring aspect might be a red herring, reflecting somewhat different cadence or power between the rings. Pedal bearings (already mentioned) is a good shout, play in the rear hub. At a push, perhaps a creaky QR. The clunk points to BB bearings, though. You’re going to have to replace them at some point, so won’t be a wasted investment if swapping bearings doesn’t fix it.

Indeed, that's the next step. Being a pressfit that means a visit to the lbs - not something I have the tools for.

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IME when I ran an LBS any press-fit BBs were potentially problematic - usually a regular click - some (like Praxis) include Loctite 641 in the fitting process. 

[Milkfloat]

Does it also do it out of the saddle, I once changed a BB30 to no avail to finally work out that the saddle bolt needed tightening. I have also experienced creaks/clunks due to a dry seatpost (fixed with carbon paste). Finally, if it is occurring just on one ring, check to make sure that you are not clipping the end of the  front derailleur cable, the angle of which changes depending on which gear you are in.

[zigzag]

a worn chain can move on the chainrings making a tick/clank noise. if it is worn in better with a large chainring, it may not mesh so well with less frequently used small ring.

[Gattopardo]

Had play/slight in a rear cog that caused a clank.

But not one clank for every pedal rotation, presumably?

Yes, I thought it was odd too.  But on the doing one thing and waiting to see if the clonk remained, the rear cassette and hub were cleaned and the cassette bolts were tightened and that caused the pedal rotation clunk go away.

[toontra]

Just back from the (very good) LBS.  They installed a new pressfit BB.  Loctite was applied

Still *** clonking in exactly the same place - every pedal rotation when pressing hard on the left crank when it's at at 10 o'clock (downward), but only when in the small chainring.

The very last thing to try is replacing the chainring, but I really can't think a worn or damaged chainring would cause that kind of noise - a deep banging which reverberates through the frame.

[hatler]

I had a pedal rotation clank recently and it was simply dry threads in the pedal/crank interface.

[toontra]

I had a pedal rotation clank recently and it was simply dry threads in the pedal/crank interface.

Ah OK.  Don't think I've tried that 

[LittleWheelsandBig]

Try different pedals and/or shoes too. Movement at the cleat can be amplified by the crank and frame and sound quite different. None of that applies to a ‘small chainring only’ noise though.

Does it make the same noise when you apply pressure when you are stationary or only when you are moving? Standing or seated or both?

[toontra]

Try different pedals and/or shoes too. Movement at the cleat can be amplified by the crank and frame and sound quite different. None of that applies to a ‘small chainring only’ noise though.

Does it make the same noise when you apply pressure when you are stationary or only when you are moving? Standing or seated or both?

Not the shoes (happens with several pairs) but yes - pedals are the next thing to try.

[Canardly]

Have you nipped up the arms?

[toontra]

Have you nipped up the arms?

Yep.  Everything checked, cleaned, greased and torqued appropriately.

[LittleWheelsandBig]

Does the noise alter when using different cogs across the cassette?

[toontra]

Does the noise alter when using different cogs across the cassette?

Yes.  The bigger the cog (lower gear) the louder the clonk.  On the biggestl cog it's by far the loudest, but barely noticeable 3 cogs up. As mentioned absolutely no noise on the large chainring no matter what cog (even if pushing hard on the biggest cog).

Thanks for taking an interest LWAB.  This is starting to do my head in    It makes going up steep hills a noisy business (and embarrassing if in a group) when you really want to be concentrating on getting to the top in a timely manner.