I am working on cleaning up an older Klein with 7 speed freewheel 13-26, and Shimano 600 drive train. The existing chain was rusted and probably worn beyond use. I placed a new SRAM 870 6/7/8 speed chain after major clean up of components. Now I get a skipping in the 17, 19 and 21 sprockets. My indexing is spot on and I have aligned the hanger perfectly. As far as I can tell looking down at the FW is that the chain appears to be skipping forward when I apply pressure vigorously to the pedals (only when riding). It does not skip with soft pedaling. Note that I also replaced the 10 tooth jockey wheels with new ones. I can barely perceive the machining, but it is present in the high and lower sprockets, while the groove of the inner sprockets are smooth.

So after all that my guess is that the new chain on worn sprockets are causing my problem. The old chain wore with the sprockets and did not skip. Am I on the right path? Is there a quicker fix than ordering a new FW?

Thanks in advance,
Alan

You are exactly on the right path and you are experiencing the classic results of using a new chain on an old, worn cassette/freewheel. This is particularly noticable with the smaller, most used cogs as you have seen. At this point, a new freewheel is the only cure. Next time either replace the chain more frequently or plan on replacing the chain and freewheel together.

I happen to have a new (less than 100 miles) Shimano 13-28 on my Peugot Triathlon I restored. If the 600 series Derailuer can handle the 28 sprocket, then I can just order a replacement FW for myself and get my friend up and running without the skipping (I am doing this for a friend). Thanks for the reply. It reinforces what I thought I would have to do anyway.