New chain problem...

[John Saxby]

Julio,

I have a 36 x 17 chainring and sprocket on my Raven. The 36T ring is a Surly stainless-steel item. This past summer I had some chain noise for which I had difficulty finding the cause, and it was difficult to get rid of it. The chain was making a clickety-ripply metallic noise on the power stroke, especially on hills. (I'm not sure how much damage the noise would have caused, but I didn't like it.)

It appears that there was some incompatibility between the steel ring and my chain.

Currently, I am using an SRAM 971 chain on a new Surly 36T ring, and this appears to have solved the problem. 

The 971 chain is slightly thinner (11/128ths inch) than the SRAM 830 and 870 chains, and the KMC X8.93 chains (all 3/32nds inch), which I had been using.   (The difference is very slight, about .0008 -- eight thou -- of an inch.  Can this make a significant difference?  I guess it does.)

Here are the main points in what happened:

• My steel chainring had about 9500 kms on it, since I installed it in mid-2015.  The teeth showed some wear, and the ring as a whole had become more oval.  My local bike shop recommended changing the ring; I wanted to just reverse it, but agreed to replace it.
• The Canadian distributor had no Surly 36T rings in stock, so I used a 36T Sugino alloy ring for about 1,000 kms while we waited for the new Surly stainless ring. The chain noise was less, it but continued.
• When the Surly ring arrived, I changed the old chain (a KMC X8.93), which had about 4,500 kms on it.  But, the noise was worse with the new KMC chain (!! ??)
• So, I took off the new KMC chain & installed an SRAM 870 chain. I checked and re-tightened the chainring bolts at the same time -- one had been very loose.
• The SRAM 870 chain at first seemed to have solved the problem. After about 150 kms, however, the noise came back
• In emails with Dan about the mystery, he mentioned that he uses an SRAM 971 on his Nomad.  So, I bought one of those and installed it.  So far, it seems to work -- the noise has disappeared.

Hope that's helpful, Julio -- good luck!

John

[mickeg]

John, you mention your ring had oval wear.  Not exactly sure what you mean but I think you are saying that the part of the ring that is at the top and bottom when your crank arms are oriented fore and aft gets more wear, as that would make sense since that is when the tension on the chain would be greatest.  If you still have the ring, you could turn it 90 degrees if your crank spider has four arms, or 72 degrees if it has five arms.  That would spread the wear out a bit.

[John Saxby]

George, I think I condensed things a bit too much, and created confusion:  The guys at the shop said that the ring was "ovalized", and they thus thought that that was contributing to the problem.  I took that to mean that the tight spot was unusually large, and it's true that the old Surly ring produced a noticeable and extended tight spot in the chain.

I wasn't too fussed about the tight spot (long acquaintance with British motorcycles), and would have just reversed the ring, had I been doing the work.  Had I rotated the ring a fifth of a turn, though, would that have altered the tight spot? 

In the event, having a pretty good rapport with the crew at the shop, I said to go ahead & swap out the ring. (When all was said & done, they didn't charge me for any of their time, because they couldn't find the source of the problem.)

It turned out that the temporary Sugino ring (a nicely machined alloy item) improved the tight spot considerably, so that the chain tension was quite a bit more constant than it had been with the much older Surly ring.  But the chain noise, though reduced, was still present.

(I should have noted that the chainline was spot-on at 54 mm, except for being slightly off by .5 mm at one point of the circle.)

In the end, I'm still a bit puzzled by it all.  I first thought that the problem was due to the wear on the teeth of the old ring -- looking at the ring from the right side, the rear "flanks" of each tooth had been flattened slightly, the first stage of indentation.  But then, the rattly/clickety noise continued with the new Surly ring, and with different chains (SRAM 870 and KMC), disappearing only when I switched to the SRAM 971.  Even there, I haven't been able to put on enough mileage this autumn to be sure that the problem has been fixed. 

Cheers,  John

[mickeg]

I think it is rare if you do not have a tight spot somewhere considering how easy it is for manufacturing to get a crank slightly off of being exactly concentric with the bottom bracket spindle axis.  And there usually is a bit of slop in how well the chainrings fit on the chainring bolts, just as there is a bit of slop in how the chain ring bolts fit on the crank arms.

On my Nomad I have a very low budget crankset and low budget chainrings.   Thus, I probably have more slop than typical in how things line up.  I mentioned in a different recent thread (a Rohloff went for a swim) that:
When I put on a different chainring, I always backpedal the crank several times to see if the chain has a uniform amount of slack for the entire crank revolution.  Sometimes the chainring is not quite concentric with the crank, and then I loosen the chainring bolts a bit and try to shift the ring position a bit on the spider and retighten the bolts to try it again.  And when I have a reasonably consistent amount of slack, then I finish tightening the bolts.

Since I use a different chainring (44T) around home than when I am traveling (36T), I am changing chainrings much more frequently than I suspect most Rohloff owners are.  Thus, I am reasonably practiced at trying to get the chainring concentric with the bottom bracket spindle axis.

I guess the bottom line would be that when you do any crank or chainring work, it is a good idea to check it by turning the crank backwards for half a dozen revolutions to check to make sure that the amount of slack does not vary too much.

And even then, by hard pedaling you might be able to shift the chainring on the crank spider by a bit later which could cause a tight spot to return.

If you are working on a Rohloff bike, it is my experience (limited to only my one Rohloff) that the hub is of a high enough precision that the rear sprocket will be very close to concentric with the rest of the hub.  But on other IGH hubs that might have less precision, the hub might be slightly out of round and that could cause a tight spot too.  I recall having some difficulties in that regard decades ago with some Sturmey Archer 3 speed hubs.

[John Saxby]

Thanks for that useful tip, George.  I'll try it next time -- I expect that there will be a next time!

I recall reading suggestions in other forums, on how to reduce a tight spot/get more equal chain slack (or tension).  They were less gentle and elegant than yours--move the main tight-spot links close to the ring and give them a smart whack with a small hammer(!!) The intent was to move the ring ever so slightly on the square taper.  I did try that--not without some anxiety--when I was running a 38T ring at the front, and it actually seemed to ease the tight spot (which wasn't all that serious with that ring anyway.)

I'll probably ride my Raven only when spring comes in a few months' time (late April), and before I do, I'll follow your advice.

All this seems quite distant as I write:  we've had a dose of Saskatchewan weather the past couple of days, clear & cold and down to -10 or -12 C at night, -18 windchill. Tonight & tomorrow, we're due to have 20 cms of snow. Added to that, both of us have colds (now in retreat, thankfully) and I'm recovering from surgery on an arthritic left big toe--happily, that went well with an awkward bone spur removed and years and years of accumulated crud removed from the joint.  Reckon I'll be able to get back to gym bef Christmas, though--certainly by the new year--and I'll take a bike when we visit our family Down Unda in March.

Cheers,  John

[jul]

My crazy noise transmission has almost disapeared after to have ride 200-300 kms, only when i climb i can still hear it a little..
I think it's because my chainring is in stainless steel, that it was long to wait the noise disappears.

[John Saxby]

That sounds good, Julio -- c'est à dire, not much sound at all!