Ggrhh. Why does my chain keep breaking?

{quote]Why to people keeping banging on about chainline on multigeared dérailleur bikes?[/quote]

Imagine your chain working at the limits of its flexibility. Now imagine it working but extended another 2.5mm the wrong way because the installer got the wrong amount of spacers on the BB. Do you think the extra stress will cause the chain to snap more often or less often? Can we do one on greasing brake pads to reduce noise now?

I would second the new chain and cassette. You won’t of had 2 faulty chains but may accumulate damage to a chain tht’s been running with problems. The cassette may have worn to the old chain and be trying to stretch the new chain. My stumpy is prone to wearing the small chainstay pivot bearing, allowing movement and occasional gear skipping under load.

Good luck with your diagnostics.

Imagine your chain working at the limits of its flexibility. Now imagine it working but extended another 2.5mm the wrong way because the installer got the wrong amount of spacers on the BB. Do you think the extra stress will cause the chain to snap more often or less often? Can we do one on greasing brake pads to reduce noise now?

2.5mm get real –
chains can easily deal with that as they are more flexible than required. though despite that to be fair I moved a spacer from the drive side to the non-drive side on my 1×9 so the chainring was more in line with the big sprockets – because despite knowing my chain will not break it is better to get a straither run for the bigger sprockets

chainline is clearly not the cause of the OPs issues – and perhaps a bit of a red herring

greasing brakes – drum brakes – yep greasing needed

MrK 9 speed Shimano chains (which HG93 is) are not directional. It is 10 speed that are.

my directional shimano chain was 9 speed. at least, that’s what i asked for. if it had obviously been 10 speed i would have returned it…

Only thing to add is another recommendation for kmc, I used to regularly break shimano and sram chains, since moving to kmc I,ve broken one once, and entirely my fault for changing front down whilst sprinting uphill. It took a couple of chainring teeth with it to

KMC chains all the way for me.
Never had any issue with them and they tend to last far longer than the SRAM 991’s I used before.

2.5mm get real –

Thanks for your opinion but if you don’t mind I’ll be ignoring any further technical input from you.
At least some of the Shimano 9 speed chains are directional, the instructions supplied with them definitely show which way a newly joined chain should travel. The instructions are bound to be online somewhere.