Clem H Chain Suck Issue

[Bill S]

Hi all,

We recently purchased a used Clem H for my wife, and the previous owner said she had only ridden the bike about 100 miles. She was the second owner, and said that the first owner also did not ride the bike much, which I believe because there really wasn't a scratch on the bike. 

On the first ride, when my wife shifted the front derailleur the chain sucked up and got stuck in between the chainring and the frame. I was able to pull it out and we kept riding, but the same thing keeps happening. It doesn't happen every time she shifts in the front, but it has happened about 5 different times, and has happened every time she's ridden the bike.

The front is a double with a small 24 tooth chainring and a large 38 tooth with microshift thumb shifters. I can't recreate the issue when the bike is in the stand, but I did try putting a new chain on to see if that would make a difference. I also put in slightly smaller spacers between the chainrings and made sure that all the teeth were aligned on each chainring, but so far nothing has made any difference. This issue has happened when shifting from the small ring to the big ring and also from the big ring to the small ring.

I think the next step is to replace the chainrings, but I am wondering if anyone else has had this issue? Should I swap the 38 tooth with a 36 or a 34 to reduce the difference in size (although I know 38-24 is how it comes from Riv)? Maybe I can try putting some zip ties where the chain is sucking up into the frame? Is it possible that the wide (26x2.35) tires that came with it are causing an issue, since the chain is pretty close to it?  Any insight is appreciated. I've included some photos below.

thanks!

Bill

[Bill Lindsay]

I have three thoughts on the matter.  Maybe four...maybe 5.  Some, or all, maybe don't apply to your situation.  

1. The first photo has the chain sucked all the way around to the top of the cranks, and my brain goes to "why did they keep pedaling that long?".  It's like when you are driving on a mountain road, overshoot the corner and are now in the gravel, and you keep your foot on the accelerator for one second...two seconds, and keep driving off the cliff.  Try to hear and feel it happening and stop.  Don't drive through the gravel and off the cliff

2.  Chain suck is always much worse when you shift the front under load at low RPMs.  When I taught new riders how to shift the front, I told them the front shift should be dictated by the terrain, and should therefore be obvious and easy to see and easy to anticipate.  The rear is for "feel".  On a 24/38 in front, the 24 is for pedaling up steep inclines.  The 38 is for everything else.  The classic mistake that inexperienced riders make is they are cruising along at a good clip, get into a really high gear because they are cruising along fast, then they stop at a red light.  Then the light turns green and they are grunting with all their weight on the pedals going "darn, this gear is way too high!" and slam the front shifter while still pedaling with all their might.  The solution to that is shift to a good start-up gear before you come to a stop so there is no shifting under load.  The axiomatic truth of front shifting is that the lighter your pedaling force the better the front-shift will be.  

3.  What happens during chain-suck is that the chain moves over from the OLD ring to the NEW ring.  For a fraction of a second the chain is engaged with both.  Pedaling force kind of rams the chain into position on the NEW ring.  If the teeth are lined up just right that can make a pulling force on the part of the chain that is still on the OLD ring.  That can make the chain "stick" to the teeth of the OLD ring, and so instead of rolling off the ring, it stays stuck to the old ring and gets pulled up.  Hooked or otherwise damaged teeth can make a ring "stickier".  A chain that's a hair too narrow can make a chain more likely to stick to the ring and get pulled up.  The way the two rings are clocked to each other can influence the way the teeth line up.  I'd recommend you make a black mark on the 24, and on the crank arm.  Then remove the 25 and clock it by 1/5th a turn.  Many 24T rings have an arrow on them and that arrow is intended to line up with a similar feature on the 38.  Look for those features, see if they are lined up, and experiment with different orientations.  

4.  Big picture, it seems that a good mechanic who you trust should look at the bike, and a good rider who you trust should review front shifting techniques with your wife.  One way to think about it is that you should always shift the front before you need to.  The rear is for shifting right now because you are in the wrong gear right now.  

5.  These issues are one contributor to why so many bikes today are 1x.  Rear shifting and front shifting are entirely different actions, and rear shifting is close to fool proof.  The only truly fool proof front shifting is no shifting.  

Finally, never cross chain small-small, EVER, even as an intermediate step to get to another gear.  Small-small is hot lava.  Stay away from the hot lava.  Only use the 24 when using the bigger half of the cassette.  

Best of luck getting it sorted.  

Bill Lindsay

El Cerrito, CA

[John Robert Williams]

Hello Bill & Bill! 

YIKES! So sorry about the frame scrapage!  That hurts to look at! DARN!

I agree with Bill L on his well versed knowledge. 

May I add my two cents? 

I cannot tell from the bike photo what cassette ring count is on the Clem. Is it a 9 speed? 10? More?

A narrow chain for a 10 speed may not play well with the rings on the Silver crank.

Back in the 80's & 90's, triple MTB cranks with "granny" rings were popular and the dastardly chain suck was common.

Mistake #1 was shifting into it by accident. We had rigid forks and sometimes, overshifting happened on a sudden jarring bump. 

The tiny inner ring really didn't interface all that well and sure enough, the frame/chain jam would happen.

My simple suggestion is to turn the low limit screw on the front mech to not allow left hand shifting to the small ring. 

(Agreeing with Bill L., operator error) Have your spouse only shift with her right hand. 

I would change the chain to accommodate the rear cassette and the front rings, and learn for the time being to only shift in the rear.

If your uphill grades are steep, possibly a wider range rear cassette is in order. If the terrain is not steep, the 38 will get her everywhere.

Chalk up another win for 1x systems. Simplify, whenever possible. That bare steel will need some TLC.

Happy Trails, 

JohnRobertWilliams

Traverse City, MI

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John Robert Williams

[Bill S]

Bill and John,

Appreciate both of your thoughts and suggestions! We will of-course touch up the frame so it doesn't rust in the future, but yes- pretty gnarled.

Cassette is a 9 speed 11-34t. Converting to a one-by setup is certainly an option, and maybe I'll go that route if it comes to it. We're in Pennsylvania, so most rides end up with some steep hills where it is nice to have the wider range. I would put on a larger rear cassette if I went that route.

I do really like Bill's #3 suggestion above, regarding the alignment of each ring, and will give that a go to see if that helps.

It could definitely be operator error as well, which we did talk about. She's been riding a lot the last 4 years or so on a 98 bianchi volpe which we set up with bar end friction shifting - so she isn't new to shifting by any means. It has a triple up-front and she never had any issue with that, but the 2x could be a different animal which takes a bit more thought since its a larger jump between the rings. If we're out together on the weekend we'll typically end up doing around 40-50 miles on varied terrain. I will try and take the bike out myself later today, and see if I have any issue. The chain-suck was just happening so often that it seems like there might be something I was missing/figured it was worth asking to see if anyone else had the same happen with a 24/38 since I know that is an option Riv has on thier completes.

[iamkeith]

 I agree with everything Bill L. said, above.  Normally I'd add that this isn't a model-specific issue but, in this case, the fact that it's a Clem makes it a little more interesting.  But in the opposite way... in that I would have thought these problems more rare.

  

I have a 59cm Clem H, and it’s the only bike I've ever had that I will regularly and INTENTIONALLY cross-chain (big/big or small/small chainring/cog combinations).  The chainstays are so long that the chain is not angled or flexed very severely when I do.

I also have mine set up as 2×9, with 24/38 & 12-34 and friction shifters.  Simple chainrings with no ramps.  Long-cage rear derailleur to take up lots of chain slack.  Shimano CX-70 front derailleur, so the cage shape follows those smaller chainrings pretty well.  I don't have any trouble at all but, as Bill suggests, I rarely if ever shift the front under load  because of habits learned by cutting my teeth before indexing and shift aids existed.

Other things worth considering, based on my own satisfactory experience:  

Too much chain slack can sometimes precipitate chain drop because it bounces off.  This could be exacerbated by the long stays / extra-long chain.  Make sure you have as few links as you can get away with, measured in the big/big combo.

Chainline should be less critical than most bikes, but maybe I got lucky and found an ideal one.  I can measure if you want to experiment with bb spindle lengths.

Obviously, the limit screws need to be adjusted properly but, maybe try setting them by finding the position where you CAN'T shift to the next chainring, and then going just a nudge beyond that.

How far are the two chainrings separated laterally?  Sometimes too narrow of a spacer on the inner chainring can cause the chain to drop past it instead on onto it.  Conversely, too thick can cause the chain to get stuck between them.

[Tom L.]

I had the same aggravating problem and it turned out to be caused by burrs on the teeth of one of the chainrings. Feel each tooth for burrs and use a file to grind them off. I opt for steel chainrings when I can now because of this. 

[Nicolas H]

In that first pic it looks like your front derailleur is way too high. It should be max 3mm above the large chain ring but it looks like it's been spaced relative to the trouser guard. 

Thanks,

Nic

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[Bill Gibson]

Is that Shimano 105 ok for these chainrings? The profile of the guides should closely match the chainrings, outer for outer, inner for inner. 105 was for a certain range large to small. Not for triples. I think.

Bill Gibson
Tempe, Arizona, USA

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[Joe Bernard]

You are correct, Bill. That 105 is meant for bigger chainrings, and it's going to be narrow for a 10- or 11-speed chain. This bike probably has a 9-speed chain. 

[Bill S]

All,

Thanks for your replies. Brief update: On saturday I was able to get the bike in the stand and inspected both chainrings to make sure all teeth were in alignment with one another. I took the crank arm off, and filed any burrs off of the teeth. I then moved the smaller chainring by 1/5 turn as suggested by Bill L above. Put everything back together and took it for a test ride myself. Chain sucked right up on about the 3rd time I shifted from the larger chainring to the small. This was on not shifted under load, so I think that rules out operator error as the problem. 

I was at the local bike co-op and the head mechanic there (and friend), who has been helping me a bit with the diagnostics, suggested replacing the 38t chainring with a 40t they had lying around as it was pretty new. This minimizes the gap between the frame and the chainring itself, so less room for the chain to suck up from, even though there is now a bigger gap between the two rings. I rode the bike around a bit after that change, and the problem hasn't resurfaced again - but time will tell if it actually solved the issue.

Interesting comments about the front derailleur as well. I brought the bike over to my LBS last week and had the mechnic there throw it in the stand, and he had the same thought. He said everything looked good, but did mention that the 105 derailleur was a bit higher than he would like, but it can't actually go any lower because the bottom of the derailleur is right at frame height. This is because as you all mentioned, it is meant for larger chainrings. I haven't had time to track down a new front derailleur yet, but I will replace that as well.