Sprocket wear

That would depend on how much the chain has worn before it was replaced.
By replacing chains often, or keeping spares to use in rotation, you can make sprockets last much longer.
If you let the chain get worn out before replacing it, the sprocket will not work well with a new chain and the new chain will wear out very quickly.
Replace the sprocket when it doesn't seem to mesh perfectly with your new chain. Or

If you have just bought a new chain to replace a worn out one but you don't have the sprocket yet, then just keep using the worn chain.

10 full links of new chain measures 254mm
Replace the chain when it stretches (wears) to 255.5mm
Replace the chain and sprockets if you've let it stretch to 257mm (so keep using the worn out stuff, either until the new chain and sprockets arrive or until they stop working at all)
 
usually, one will be able to see a marked difference in the two sides of a tooth - when the side that pulls the chain looks more worn than the other side of that tooth, it will begin to damage the chain
 
I had one strip out on long s**t their disasters for shake downs, just look at it the chain will just rip across those teeth wearing down even more.
If your suspecious order right now a couple of them. Otherwise you may have a 2 week down time waiting for mail.

Just yesterday stop in a Best buy get new phone had my bike lock out front went back out of the store some big black ape hanging around my bike notice spark plugs wire had been severed never heard of that problem could of wrestle with the ape man but instead always carry a tool bag with spare CDI took 10 minutes to fix before the rest of Spankies gang to show up.
 
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