Weird noise from down below.

[slowmotion]

I wonder if anybody can help. I was out riding my daily lockdown ten miles this evening when a noise developed somewhere near the pedals. It doesn't have anything to do with the front derailleur because it only occurs once per revolution of the cranks and gear shifting doesn't alter it in any way. It sounds like a slight "graunching" noise for about 45 degrees per revolution and it happens at the same position in each revolution. If I unclip my right foot and only pedal with my left, it stays the same, but only pedalling with my right foot makes the noise go away. I would be very grateful for your awesome advice.

Thank you.

 

[I like Skol]

Try oiling your left knee?

 

[I like Skol]

On a serious note.....
What pedals and what bottom bracket?
Hollow tech II tends to eat through LH bearings in my experience. Any play detectable if you waggle the cranks sideways?

 

[slowmotion]

Try oiling your left knee?

I drilled a hole in sideways with my Ryobi and squirted in some Finish Line Green, but no luck.

 

[slowmotion]

On a serious note.....
What pedals and what bottom bracket?
Hollow tech II tends to eat through LH bearings in my experience. Any play detectable if you waggle the cranks sideways?

The bike's a Specialized Secteur Elite (2010) with triple Shimano 105 gearing. It's been pretty lightly used because I've ridden another bike as well since then, and I'm a pretty crap cyclist anyway. The cranks are Shimano. The pedals are Shimano A520s. There's no slack if I put a lateral force on the pedal end of the cranks, and there's no lateral side-to-side movement. It feels pretty good whichever way I tug or push.
Odd business.

BTW, the bottom bracket has BC1.37 x 24 Road written on the housing on left and right sides. It's the non-drive side that seems to make a noise.

 

[I like Skol]

Yep, Hollowtech.

My guess will be the left cup has got some moisture in and killed the bearing. They are not very waterproof and I think the RH one is more protected because the chainring spider covers it so it outlasts the left. I have a drawer full of good used RH cups, kept just in case a freak reversal of reality occurs and I find a left one out-survives the right!
Distance covered won't be a major factor in the lifespan of these bearings as it is the moisture ingress that kills them prematurely. Washing a bike then putting it away is not good for them either..... I don't wash my bikes for this very reason

 

[I like Skol]

Pop the cranks out and you can check how the bearings feel when turning them by hand.

 

[slowmotion]

Pop the cranks out and you can check how the bearings feel when turning them by hand.

Why take off the cranks? I can take the chain off the drive side, spin the axle and listen without faffing about with the cranks.

 

[Yellow Saddle]

Why take off the cranks? I can take the chain off the drive side, spin the axle and listen without faffing about with the cranks.

Do exactly that. Use a stick as a stethoscope. A good bearing whooshes. A bad bearing rumbles.

 

[I like Skol]

Why take off the cranks? I can take the chain off the drive side, spin the axle and listen without faffing about with the cranks.

Because Hollowtech is so easy to remove/refit and any noises can be quite subtle so actually checking how each cup feels when turned with your fingers can give a much more positive diagnosis than just listening.

 

[Yellow Saddle]

Yep, Hollowtech.

My guess will be the left cup has got some moisture in and killed the bearing. They are not very waterproof and I think the RH one is more protected because the chainring spider covers it so it outlasts the left. I have a drawer full of good used RH cups, kept just in case a freak reversal of reality occurs and I find a left one out-survives the right!
Distance covered won't be a major factor in the lifespan of these bearings as it is the moisture ingress that kills them prematurely. Washing a bike then putting it away is not good for them either..... I don't wash my bikes for this very reason

Drill a hole in your BB at the lowest point, to drain water. It really extends BB life. Further, Shimano does provide individual left or right side cups. Not many shops like to sell only one cup though. In our shop we sold about double left to right.

 

[Ajax Bay]

https://www.cyclechat.net/threads/thoughts-on-bottom-brackets.243977/#post-5484979

 

[slowmotion]

Due to impressive sloth, I didn't quite get round to investigating the problem further. I took the bike out as usual at 7:45pm and the graunching noise had mysteriously gone. Very odd. I'm sure it will return, at which point I'll take your kind advice. Thank you.