Originally Posted by
madpogue
So in short, cleaning an already-way-too-elongated chain can make it skip, right. Alternate interpretation - enough gunk on an already-way-too-elongated chain can mask the fact that it's way too elongated. I can just imagine how hard that can be to explain to an "average" customer.
Still, that's a much better explanation than claiming that cleaning the chain MAKES it longer, as the OP was told. In short - if cleaning a chain makes it skip, it was probably shot in the first place. That would have been a more meaningful explanation than the "man-splanation" the OP got. Goes right back to why it's handy either to have a chain checker, or to measure it yourself, so you go into the shop already informed.
Yep, a too long chain that doesn't engage the teeth correctly will skip. Another thing is that a dirty chain will wear out freewheel/cassette teeth prematurely. This will also induce skipping, even with a brand new chain.
BITD of freewheels, when the skipping started, you knew it was time to replace the freewheel. The usual ROT was two chains per freewheel. This might be I dunno 10-12,000 miles or so. Keeping your chain clean helped extend the mileage. This skipping issue doesn't seem to come up anymore. Maybe improved materials, tooth geometry, chains and derailleurs all work to prevent it.