cnskate

I have cobbled together a pretty nice Frankenbike with Campy Chorus 10 speed shifters, derailleur, cassette, and a Shimano Dura Ace standard crank and Shimano 105 10 speed chain. Everything works great except I cannot for the life of me get it to stop wanting to pop out of the fourth smallest gear in back when I stand on the pedals. Do I just need to drop the dough for a Campy 10 speed chain? thanks

tanguy frame

try it and see...then let us know.

Al1943

Were the cassette and chain new or worn? Does the chain act like it's trying to shift to another cog when it skips? If so the cable tension needs adjusting.
A good 10-speed Campy chain would be a good investment. It will last longer than a Shimano.

cnskate

New chain and a used cassette. I've messed around with the cable tension a bunch to no real effect. Maybe a trip to the friendly local mechanic is in order, although he might just tell me to buy the Campy chain too.

Steve530

Did you adjust the derailleur per Campy instructions?

Al1943

This often means that the old chain was run on the cassette too long and the most used cogs have worn to fit the old stretched chain. If so you will need to replace the worn cogs or probably the whole cassette. A chain needs to be replaced by the time any one foot interval has stretched to 12 1/16 inches.

DaveSSS 

If you have a used chain, with even a few hundred miles on it, it will probably work fine. If you buy a new cassette, you could use it for only a few hundred miles, then put the old one back on and probably get another 2-3,000 miles of use from it.

As others have suggested, that 4th cog is probably the most-used and will no longer mate with a new chain.

cnskate

Worn cog sounds plausible. When I bought the wheels and cassette second hand the PO said he had completely worn out the old chain. The 4th and 5th look maybe a tiny bit more worn than the others. Would it be very noticeable to the naked eye? Thanks for the help.

Al1943

In some cases worn cogs are obvious to the naked eye, the worn teeth may have more of an asymmetrical shape with excess wear where the chain roller engages the teeth. But, modern cassette cogs have various designed asymmetrical shapes to aid in shifting.