Originally Posted by
Leisesturm
Chainrings do not usually wear significantly. Most last for the lifetime of the bike. Cassettes and chains on the other hand do wear. "Everyday since 2016" sounds like worn chain and/or cassette, and the advice is usually to replace both together, if either one is found to be worn.
I'm replying to this post because I replaced chainrings on two bikes recently. Both 36T middle rings on old 110 BCD cranks. Both bikes exhibited "crunchy" feel in the middle ring with a new chain. A new ring resolved the problem. And oftentimes (and in one of my cases) chainring wear is invisible. "Looking" at a chainring is useless to diagnose a chainring wear issue. You have to test ride it (and know chain replacement history of the bike in question). And while working on the wife's single mountain bike, I realize her middle ring may need replacing as well. Chainring wear manifests itself two ways: simply worn teeth (pulling edge wear) and chain suck. Now the latter is not an issue with timing chains, but it's a good indicator of wear in triple-chainring scenarios where visual chainring wear is not obvious.
So, "Chainrings do not usually wear significantly" is not really true. Chainrings wear far more slowly than cassettes, but they do wear. And four years on a tandem could easily wear out chainrings on a tandem. And the ICS system uses much smaller rings:
"
ICS also allows a great range of gearing because the
chainrings are half the
size of those on conventional drives. The 12-, 18-, 24-, 30-tooth
chainrings are equal to conventional 24-, 36-, 48-, 60-tooth
chainrings."
Well, "half the size" translates to "twice the wear" since now half the chainring teeth are sharing chain loads. Additionally, a bike that hasn't had appropriate and regular chain replacement will wear out chainrings even faster. Timing chains can wear faster than main chains on tandems under many circumstances. (I spoke to a DuMond Tech rep at Interbike one year and he and I were discussing tandem timing chain wear. He said their tests indicated timing chain wear was THE issue with tandems.)
So the OP's symptoms point directly to chainring wear in my opinion. I'd at least inquire into what maintenance the bike has gotten over its four years, specifically chain replacement intervals. At the VERY least, I'd ask the OP to hold a ruler up to the chain and see how much "stretch" is observed. Since it's a timing chain, I'd suggest measuring 24" of chain to better reveal the amount of stretch. Just multiply the usual wear metrics by 2: So 1/8" wear (or more, obviously) in 24" means it's at "replace" stage. More than that means the rings have been suffering increased wear with every ride and skipping is a very real possibility if wear has gone off the charts and really affected chainring teeth.