Hi all,
I just completed a winter stripdown and overhaul of my 9 month old bike. I split the chain with a Park Tool CT-5, pushed the 2 original pins out and after cleaning and relubing the chain (Prolink Gold) I rejoined it with a genuine KMC 9sp missing link. It all went smoothly, and all works perfectly except... on 9th rear sprocket the chain now jumps, rather like a worn chain, but twice. Once as the link goes onto the cog, and once as it comes off the other end.

Chain: Shimano HG50 9 speed. <0.75% stretch (way less)
Link: KMC 9sp missing link, bought from a reputable, large high street store
Cassette: Shimano HG 11-32 9sp

What appears to be happening is that the 2 pins on the missing link stick out a *tiny* amount from the plate, and stop that segment from sitting down into the sprocket. Why only on 9th I don't know.

Has anyone come across anything like this before? I'm 99% positive I've not missed out any spacers between 8&9 or suchlike, so I'm wondering whether to file to end of the pin down

Cheers
Jon

Never had a problem with that missing link. Are you sure both pins are engaged in the side plate?

There are very slight differences in pin/link width between the various chains of the same "speed" spec. But these differences are in the order of 0.1mm or so (about 4 thousandths of an inch).

You could try a different connection link. The same brand as the yet to be known chain. The chain and cog could be so worn that only an old worn link will run skip free. The connecting link might not be fully snapped closed (as mentioned already by Wanderer). You could have a bent tooth. You could have a missing cog spacer (both of these are doubtful though). Andy.

Hi Andrew,
I did say that the chain is a Shimano HG, in fact it's an HG53. So the KMC link really ought to work (the packet certainly claims so)
It definitely isn't worn either, I tested it with a chain stretch checker and it's easily passing the 0.75% test.

I have another KMC link in the same pack which I could easily try...

Best regards
Jon

Any chance that the high limit screw needs to be let out a skosh? If it were just a chain width issue, I'd expect it to skip on just about any sprocket, not just the smallest.

I use KMC links on 9spd Shimano chains, as well as KMC, and Nashbar chains. Never once had a problem

Maybe try measuring ---- link may be mismarked/mispackaged.

I think I would also notify KMC to see what they say.

Jon- Yes, now I read the chain details. If all else fails one starts replacing a part at a time. ThermionicScott also makes a good point. Andy.

That was my first thought too, but even with lots of adjusting of both the shift cable and the stop screw it didn't affect the problem. It is odd that it's just the 9th cog, which is why I will be hunting very carefully in case I dropped a spacer somewhere, for between the 8th and 9th cog, but I was very careful...
It doesn't *not* fit, it just doesn't sit into the slot as easily, so tends to ride up. I'll take a look tonight at why it's different on the other sprockets, and also whether the 9th sprocket offset is odd. Mind you, all the original links work perfectly/

I'll take a caliper to the pins and check them against the other pins, but I'm pretty sure they'll be longer, not least because the HG53 pin ends are flush with the plates, unlike say the HG73 which looks (from photos) to have sticky-out-bits, for want of a better term!

Cheers
Jon

...I know you measured your chain stretch at <.75 (you said so), but this sounds like exactly what would happen if the chain and that cog were a little worn.
i.e., the chain and cog are worn just enough that the new missing link, which is not worn, is catching and skipping a little because it's a bit off from the rest.

I think that if it were me, I'd try a new chain and cogset, and see if that fixed the problem, or at least remeasure the chain stretch using a different method like a straight edge.

I'm not sure what you mean by 9th sprocket. Do you mean the 11 or the 32? Clearly if the link works well on 8 of the 9 sprockets, the problem is not with the link. Since you have two links, however, you may as well demonstrate this for yourself.

Interestingly, when I measured the missing link pin width with a caliper it was 6.55mm, versus one of the original pins which is 6.0mm.
Looks a bit fishy to me. It also looks to be correctly seated in the plate. I'll check the other one in the pack.

If the 11t sprocket, could it be reversed by accident. I am not that familiar anymore with 9 speed cassettes, so please forgive me if my suggestion isn't sensible.

Maybe You didn't set them firmly and so the pin to pin distance is less than 0.5".

Link on the top Drive side of the chain and step on the Pedals ?

It looks well seated, and I've been on a 10 mile ride too. Also the problem doesn't seem to be the pin distance, but the fact that the pin is preventing the link from dropping into the sprocket.

I measured the 12 to 11 tooth sprocket distance against the others, and it is correct. Also because it's HG-C it's not possible to put on the wrong way round. Good call though!

Having rechecked the chain wear it's actually started to wear a little. I can *just* get the tool in on the 0.75% setting, and a ruler over 12 links shows a 1/16" stretch, so I make that 0.5%.
My worry is that even if I replace the chain, I'll still be using a link to join it!

So, maybe the link will be fine with a new chain......

KMC 9-speed links are listed as 6.6mm pin length. KMC 10-speed links are 5.90, so if all else fails I guess you could try one of these instead, as long as it closes properly. But maybe you just have to tweak the limit screw slightly to 'centre' the chain (or at least centre the quick link pins!) on the sprocket? You've done nothing else to change anything, provided you've re-assembled the cassette correctly, and you're sure you have.

Sounds like you just have to compensate somehow for the wider pins, if possible. Try adjusting the limit screw anyway. If it's the smallest sprocket / highest gear we're talking about, you may be as well to slacken the cable right off, then re-set the cable tension and the indexing after you've adjusted the limit screw. Failing that, try the 10-speed quick links - I'm fairly sure 10-speed chains run ok on 9-speed cassettes, but maybe not vice versa, although someone who knows more than me could confirm that (none of my bikes can count past 8 - they're like, 6,7,8... um... lots!).

You can check the specs on these links (no pun intended!):
Halfords | KMC 9X Chain-Links Card of 2
Halfords | KMC 10X Shim/Sram/KMC Bike Chain Links - Card Of 2

Is the reconnected link joint actually tight? I had an issue with a chain once where it was skipping teeth in the cassette which cause the chain to pop off the front chain ring. Turns out the link where i reconnected the chain wasn't freely moving -- just had to massage it a little bit to loosen it up and havent had a problem since.

Thanks everyone for your help, I think I have resolve the issue. I measured the original link-pin that the builder put in at it was the same length as the pin on the missing link, but more central to the chain.
So, I took my Park Tool CT-5 and tweeked the missing link pin less than 1/8 of a turn to push it in, and hey presto! The link is still firmly seated around the pin, but the pin no longer catches.

I also noticed that the second smallest sprocket (which is mounted individually on the hub) is not completely true, so at some points it gets nearer the chain running on the smallest cog.
I'll strip it down again and check for anything that may have caused it not to seat properly.

Anyway, on a test stand at least the chain no longer jumps.