Chain skipping under load
 

What causes chain to skip under high load.
Im troubleshooting a mongoose with cheap components. The chain skips when it is on the 3 smaller cogs of the 7 speed freewheel. The chain is not worn as the park tool indicator suggests(.50) and it shifts smooth and does not skip while on the other cogs.

The most common problem is that the teeth on the cogs (freewheel or cassette) get worn so that as the chain is pulled forward into the expanded pocket of one tooth there isn't enough room for the next link of the chain to settle into the next space. Therefore the next link remains up on the top of that tooth and skips forward. The problem usually shows up when the chain is replaced and you have a chain with the proper spacing (1/2") running on cogs that are excessively worn.

Chain wear leads to cog wear leads to skipping.
The chain was replaced.

Enjoy