New KMC 8-99 Chains Skipping

[IronMac]

Hi all,

Not sure if this topic is specific to the Rohloff but a mod can move it if necessary. After reading through a few threads/posts I purchased a couple of KMC 8-99s to replace the KMC Z-50 on my Bike Friday NWT.

BF says on the invoice that the Z-50 is an 8-speed chain and the US KMC site says that the 8-99 was both 8-speed and IGH compatible. The size of both chains are the same as are the number of links.

So put a 8-99 on and it skips intermittently. Checked for stiff links and did not find any. Put the other 8-99 on and same problem. Put the old Z-50 on and it works even better than before.

Can anyone tell me where I went wrong? Thanks!

[wheezy]

New chain, worn sprocket, perhaps?

[phopwood]

Hi welcome to the forum,  I suspect your chain and sprockets are all worn at the same rate so you most likely need some shiny new sockets as well.


How old are sockets
Have a look at the tooth profile and check them against some pictures on the internet.

Peter

[IronMac]

Oh sorry...should have pointed out that the sprocket is perfect...it has about 5k kms on it...maybe.

I only ride on dry roads every weekend. No need to ride in the rain or muck since I can't go touring. Also, clean the drivetrain about every couple of months with degreaser, brush, then oil again.

And switched out the Z-50 only because two rulers said it was stretched.

Edit: phopwood, thanks for the welcome!

[phopwood]

The next check should then be your chain tension, but I would expect the new chain to be tighter than the old one.

Post some pictures if you have any.

Peter

[il padrone]

Tooth no. of your sprocket? A small sprocket could wear at a much faster rate such that 5,000 kms may be enough to cause wear. Maybe....

The only way to really confirm is to get a new sprocket and fit it with the new chain. My guess is that they will then run fine.

[IronMac]

Tooth no. of your sprocket? A small sprocket could wear at a much faster rate such that 5,000 kms may be enough to cause wear. Maybe....

The only way to really confirm is to get a new sprocket and fit it with the new chain. My guess is that they will then run fine.

It's a "15-tooth cog" according to the invoice.

The teeth of the sprocket look fine and I've seen pics of worn down teeth. It should last for over 20,000 kms, right?

[il padrone]

Is it a double-sided sprocket, or is the 15t the single-sided one?

Meh...... well, I have swapped my sprocket around at 12,000kms I think (17t) and will replace everything at ~24,000kms. So that will be the sprocket worn out on two sides. Your sprocket *should* last more than 5,000kms, but it really depends on what the chain is like. Place the chains together and measure 12" (24 links). If the old chain has extended to 12 1/8" or more for 12" of original links, the sprocket will be worn to the point that a new chain will skip. Your old chain doesn't skip because it is worn to fit the sprocket.

Oh, yes, the original chain - KMC Z50. A quick search and glance at the pictures, this looks to be a fairly budget-oriented chain. I would not be surprisded that it wears out (and the sprockets) at a quicker rate.

My prediction, as I said, is that a new sprocket will run fine

[IronMac]

Is it a double-sided sprocket, or is the 15t the single-sided one?

Meh...... well, I have swapped my sprocket around at 12,000kms I think (17t) and will replace everything at ~24,000kms. So that will be the sprocket worn out on two sides. Your sprocket *should* last more than 5,000kms, but it really depends on what the chain is like. Place the chains together and measure 12" (24 links). If the old chain has extended to 12 1/8" or more for 12" of original links, the sprocket will be worn to the point that a new chain will skip. Your old chain doesn't skip because it is worn to fit the sprocket.

Oh, yes, what was the brand/model of the original chain? This can lead to varied wear.

My prediction, as I said, is that a new sprocket will run fine

The 13t is the non-reversible one.

The original chain is a KMC Z-50.

[Danneaux]

Hi Mac, and welcome to the Thorn Cycling Forum!

I was out riding today when I saw your post and so had some time to think on it before replying.

I live in Eugene, Oregon where Bike Fridays are made, and dropped by the shop again several weeks ago. I have seen several Rohloff-equipped New World Tourist BFs and noticed each of them used a chain tensioner.

By any chance, could the chain tensioner have been bumped or changed tension when you replaced the chain or when the bike was un/folded? If so, this could account for the occasional skipping, quite apart from the condition of the chain. This happened to a former listmate of mine on a different forum; he worked for BF at the time and built one of the early Rohloff versions for himself. He found without the tensioner or with it set slack, there was insufficient chain tension to prevent occasional skipping.

Though it seems an unlikely contributor, it might be worth checking your chainline. I recall reading reports indicating the KMC 8-99 is more picky about such things in fixed-gear and single-speed applications than the Z-50.

Hope this helps. Please let us know how you come out.

Best,

Dan.

[il padrone]

If the sprocket is double-sided your answer is easy - turn it around. Later, when the new chain has worn out a bit, you could even rotate it back to get the last bit of life out of it.

Dan's idea about your chain tensioner is worth double-checking too.

[IronMac]

Hi Dan!

Thanks for the welcome!

Yes, my first thought when I got off the bike by the side of the road was the tensioner but when I got home both the Park Tools BBB and Rohloff manual said stiff chain link so the chain (and sprocket) has been where I've been concentrating my efforts. The chain tensioner is the same as it has always been so far as I know since you have to take out that "tensioner spring" in order to de-tension it (fully?). It is a regular Chain Tensioner and not the DH Chain Tensioner.

I've been looking for ways to adjust it by small increments but so far no luck.

il padrone:

Hope this sprockets pic helps..

[IronMac]

Frankly, I would hate for it to be the chain tensioner because just by looking at the online pdf, you need to adjust it by shims and have to measure everything in millimeters. I mean, come on!   

[phopwood]

Check the jockey wheels are smooth they have a habit of locking up on the tensioner.  Also we have talked about the rear sprocket what about the chain ring how does that look.

Peter

[Andre Jute]

Doesn't appear from the photo that a worn sprocket is the problem here.