Originally Posted by
RollCNY
This applies to roller chain, and should carry through to bike chain:
Link plate wear is uncommon as link plates are usually made out of 1040 or 1045, and through hardened. This means the hardness is full depth, and appreciable wear is very slow. Rollers are also full hard.
Pins and bushings are case hardened 1018 or 1020, with a fairly shallow case (.006-.008" on
#40 chain, which is closest to bicycle). This shallow case, with a soft under layer (think nuggat), wears quickly and shows developed wear more quickly. With bike chain having a combined roller/bushing, I would expect it to be case hardened.
My campy 10 chain with 6,000 miles on it had less than .15% elongation of about 1/16" over the full length. This figures out to be about .0006 inch of wear for each pin and pair of inner side plates. In contrast, each roller was about .005 inch smaller on the OD and about .010 larger on the ID. The side clearance between the inner and outer plates was a round .013 inch, which is about twice the clearance on a new chain. All of these amounts of wear are much greater than the pin/bushing wear. I also measured the space between the rollers and found that the original .200 inch reading had increased to about .240 inch, which is a huge increase, but it reflects the wear on two rollers - inside and outside.
What I discovered is that there is more to chain wear than just elongation. Despite the chain's low elongation, it was totally shot. It also wore one of the cogs on the cassette enough that it skipped with a new chain.
I had another bike in use at the time that had Ti cogs. After only 4,000 miles and even less chain wear, the 19 and 21T cogs wear both worn enough to cause new-chain skip.
After that, I began using the roller spacing as my most important gage of wear and also started using 3-4 chains in a fairly frequent rotation, so I never get new-chain skip and the cassette will last for the entire life of all the chain in the rotation.