pitchpole

I tried to replace the chain on my 10 speed Nishiki road bike but now it skips like crazy on the cassette. The new chain is an sram pc850 which I assumed was ok for this application. I just took what the bike shop gave me really. The teeth on the cassette are not worn. The teeth on the cranks are only slightly worn, cranks are Sugino made from that soft alloy. The new chain seems to mesh well so Im not sure what the problem is.

This bike is a Nishiki competition I believe the year is 1979.The driveline has given me nothing but grief lately.

LarDasse74

Generally speaking, installing a new chain on a bike with old sprockets will lead to skipping. The reason is the old chain has 'stretched' and worn the cogs to match. This wear on the cogs is not visible to the naked eye.

For top performance, you should replace the cassette and chainrnigs (esp. if they are visibly worn) when you remove an old chain.

You can tell if your chain is worn by measuring the length of 24 links (12 sets of inner and outer plates). An unworn chain will be exactly 12 inches from centre of pin to centre of pin. A work chain is 12-1/16 or more.

HillRider

A new chains on an old, worn cassettes or freewheel is the classic cause of chain skipping. Despite the fact you think the cogs aren't worn, they really are, particularly the smaller ones. Insatall a new freewheel and your problems should be over.


Chainrings last a lot longer and usually don't skip with a new chain unless they are very badly worn. Despite being softer than cogs chainrings are larger and have more teeth to interface with the chain and, most importantly, the chain goes onto the chainrings under tension so it tends to do what it's told.

powers2b

The above posts are correct.
Also there are tools to measure chain and cog wear.
Measuring the chain (under tension) should be a regular part of maintenance.
12-1/16 = replace chain 12-1/8 = replace cogs.
Chains are much cheaper than cogsets so as a rule I replace all my chains every year (whether I rode the bike much or not)
If you must milk the life of a chain, keeping it clean and lubed will extend the life and prevent pin wear (sometimes called stretching).
See Sheldon Brown's site for details.
Enjoy

achoo

You can see the wear on the cogs if you have an unworn one to compare them to. An unworn cog will have almost perfectly circular "valleys" between the teeth. On a worn cog, the "valleys" will clearly look oval-shaped when next to a new, unworn cog.

I find it pretty hard to see without an unworn and preferable identical cog/cassette handy, but it jumps right out at me when I do have both the worn and unworn ones.

pitchpole

Thanks for the replies guys. On very close inspection of the freewheel cogs I could see the wear spots. Since this is an old freewheel with those very tall sprocket teeth I got to thinking maybe I could do something to them to fix this based on a vague reference that Sheldon Brown made to reconditioning such sprockets on his freewheels page. I could find no detailed information about how to proceed with such a repair online but I decided to go ahead and try anyway. I had nothing to lose since this freewheel needs replacing. I used the fine sanding drum on my dremel to go over each tooth and even out the spots where the old chain had been riding. I put the bike back together and rode it around for a few miles really mashing on the pedals. The skipping is completely gone. Now I can put in some more miles till I get those new sprockets.

FBinNY 

The advice above is spot on about chain and cassette wear and how new chains on worn cassettes cause skipping. If you still have the old chain, check it for stretch, which will give you a good indication of the condition of the cassette.

If you don't have the old chain you can check the cassette condition by one of these two ways.

1- shift into the problem gear, and use an ice pick or small screwdriver to gently lift the chain away from the sprocket at the mid point of the chain wrap.
with a new chain and cassette it'll barely lift, but with wear there's movement possible so it'll lift and the chain will shift over on the nearby teeth to allow it. If you can lift more than about 3/16" you're in bad shape.

2- requires a friend. Lean the bike in a corner with the front wheel against the other wall. Shift into problem gear, and have your friend stand on the pedal to load the chain while you carefully watch the cassette. New chains and sprockets will not move but with chain and/or sprocket wear, the chain will shift forward and climb higher on the sprocket teeth, if worn enough it'll climb out entirely causing the skip.

Note both tests will tell you that either the chain or sprocket is worn, but not which. In your case, since you know the chain is OK, you know it's the cassette.

pitchpole

Here is what my rear cassette looks like, it is a pro-compe. I have put about 1900 miles on these gears since I bought it. I do not know how much the previous owner rode the bike. I replaced the chain a few times already I do ride in the rain. https://www.flickr.com/photos/49331513@N05/

achoo

It's hard to tell without an unworn identical cassette to compare it to, but if you look at the shapes of the valleys on the larger cogs and compare them to the shapes of the valleys on the small cogs, it sure seems like the valleys on the larger cogs are ovalized.

HillRider

Older freewheels could have their life extended by "flipping" the cogs over so the unworn side of the teeth faced a new chain. This doesn't work with newer freewheels and cassettes intended for indexing since they have to be installed in one orientation.