creak from left crank / bb?

Before I take everything off and refit, does anyone know what this is likely to be?

When I push down hard on the left crank I get a creak just after it passes horizontal. If I pedal gently or with just my right foot it's nice and quiet. It's a fixed gear bike, square tapered cartridge bb which is around 5 years old.

Could be the pedal, worth checking

Pedal is the easiest possible culprit to test. If it is a cartridge BB, I'd then be wondering if it has a cracked plastic cup on the NDS.

hmm ok, i'll try tightening the pedal first. It's a shimano BB, into an old (90's maybe, I don't know) steel frame.

I remember the bb didn't want to go in square when I installed it, I don't know if there'd been some cross threading previously. It's been fine for years though...

If the pedal is the problem, you will need to replace it or service its bearing. Unlikely to be unwinding itself from the crank, but who knows?

Is it a square taper?? If so take both cranks off and rotate 90 degrees. This can help if the axle is worn slightly.

Sorry have just seen that it is square taper. Worth giving that a try.

I had simillar issue. The very familiar creek when you put a harder stroke on one of the sides. Turned out to be the BB for me.
It just gave up on me one day.

the pedals are new. I replaced my old set when one pedal developed some play. I wanted to service them but they're shimano so a special tool is required, maybe one day I'll service them but I just replaced for now with an identical set, can't fault the m520s

I did ride for a few miles with the left crank a bit loose about a month ago so maybe that's worn something as you say Ben'sbb. I can try rotating the cranks thanks.

I did ride for a few miles with the left crank a bit loose about a month ago

you have fucked your cranks and the left hand side one needs replacing

Does it cause any other problems if you just carry on and ride it into the ground?

it was only a tiny bit loose! My wallet is averse to replacement

You have fucked it and it needs replacing

And the answer was.....

the bottom bracket on the drive side. It was the last thing I tried, I tightened it and everything is quiet now.

Thanks for your help