Sora groupset - new chain slipping

[cookie_monster72]

Hi all, new here so bear with me. Recently replaced my very worn chain, and middle chainring (bent) and now the new chain is slipping on the new middle chainring. I know this may be the old cassette but it seems odd it's on the new chainring only, and the cassette doesn't look THAT worn. Any advice before I take it to the LBS?

Thanks

 

[JtB]

If the old chain became very worn before getting replaced, then most likely it wore the cassette and that too will need replacing.

 

[Ajax Bay]

First, agree with @JtB - the cassette will need replacing in these circumstances (only replacing chain when very worn), even if the symptoms were not there.

the new chain is slipping on the new middle chainring.

Where exactly is the chain slipping? Not on the new chainring, surely, but maybe on one of several of the sprockets when you put a load on? Are you saying it never slips if you're in either of the other two chainrings and put a load on? Try that and if it slips (on the sprockets, as I expect it will) that confirms the need for a replacement cassette.

 

[JtB]

What Sheldon Brown didn't know about chains wasn't worth knowing.
http://www.sheldonbrown.com/chains.html#wear

Taken from the above Sheldon Brown website:

The standard way to measure chain wear is with a ruler or steel tape measure. This can be done without removing the chain from the bicycle. The normal technique is to measure a one-foot length, placing an inch mark of the ruler at the side of one link pin, then looking at the corresponding link pin 12 complete links away. On a new, unworn chain, this link pin will also line up exactly with an inch mark. With a worn chain, the link pin will be past the inch mark.

• If the link pin is less than 1/16" past the mark, all is well.
• If the link pin is 1/16" past the mark, you should replace the chain, but the sprockets are probably undamaged.
• If the link pin is 1/8" past the mark, you have left it too long, and the sprockets (at least the favorite ones) will be too badly worn. If you replace a chain at the 1/8" point, without replacing the sprockets, it may run OK and not skip, but the worn sprockets will cause the new chain to wear much faster than it should, until it catches up with the wear state of the sprockets.
• If the link pin is past the 1/8" mark, a new chain will almost certainly skip on the worn sprockets, especially the smaller ones.

I measured my chain tonight and the link pin is 1/16" past the mark, so time to replace the chain, but not the cassette.