Chain downshifting to space between front chain rings...

[andyoxon]

On a brief test of the new 10spd upgrade I've noticed that the chain (KMC X10), under certain conditions, can downshift off the intermediate front chain ring onto the space between rings, and can become jammed if pressure is applied.  The chainset is a new Spa TD-2 ("9-10"spd), middle chain ring:stronglight, small ring non-strlght zicral, and should be fine.  I have to say this was a low speed fiddle with the gears, and I think the chain was on 4th smallest rear sprocket at the time (when one wouldn't normally be shifting to the small chainring), but it still concerns me a tad that this could happen at all.   

Any thoughts on diagnosis /remedies?

[PaulF]

Is it spontaneously downshifting or getting jammed when you shift to the small chainring?

Couple of things I'd look for:

 -   front mech positioning both vertically and radially. At the outer position how much higher than the large chainring is it? Is it sitting parallel to the chain.

- have you been too conservative with the inner limit screw? Perhaps let the front mech come closer to the frame?

[andyoxon]

Is it spontaneously downshifting or getting jammed when you shift to the small chainring?

Couple of things I'd look for:

 -   front mech positioning both vertically and radially. At the outer position how much higher than the large chainring is it? Is it sitting parallel to the chain.

- have you been too conservative with the inner limit screw? Perhaps let the front mech come closer to the frame?

Thanks Paul, happens during active downshfting - probably only under certain 'conditions', I need a proper ride/ bike test.
I spend quite a while aligning the FD: 1-2mm above large ring teeth, and seems nicely lined up along the ring.  Good point I can back the inner cage edge off a bit more, to reduce the chance of the chain landing in the 'gap'.

[Brucey]

it shouldn't be able to 'skate' like that.

Many middle chainrings have shoulders on them so that the chain can't fall straight down. However the small chainring could be

a)  fitted the wrong way round; if the ring has a shoulder on it, the shoulder should normally lie to the left on a 10s setup or it could be

b) fitted with the wrong spacers. If the spacers are meant for use with a skinny steel inside chainring, they may be slightly too fat for use with a (thicker) zicral ring.

cheers

[andyoxon]

Thanks.  Will investigate the spacers...

Here is a pic from earlier...  showing chain between chain rings.  I think the small ring is on right way, as etched info is on outwards surface.

...

edit. I think the small ring is direct onto the middle ring with no spacers...

[zigzag]

it looks that the chainset is designed for lower sprocket count setups and wider chains. i've checked mine* and it's not possible to jam the chain between two chainrings - the chain simply doesn't go in there as it's too wide for the gap. i think the issue is compounded by a fact that the middle chainring is a plain flat with a few rivets, rather than shaped like they come from shimano, sram etc.

* 5703 chainset with 10sp kmc chain

[Biggsy]

It may not be an ideal chainset for 10-speed after all (regardless of what it's marketted as).

Anyway, you don't necessarily have to make it impossible for the chain to jam for it not to happen.  I deliberately increase the spacing between my middle and inner rings*.  I have the front mech set to shift vigariously and technically a bit too far inwards, but with a dog fang to stop the chain actually going too far.

* With Campag triple to help a 26T (or even 24T) catch the chain as it's chucked off the 39T - a bigger jump than the mech and everything was designed for.

[andyoxon]

Zigzag, thanks.  I also have a black 5703 chainset 'on the shelf', which I checked and gaps are narrower as you say, and with ramps/variable distance between rings ~3-4mm at most.

I measured (metal ruler only) the distances of the '9-10 speed' TD2-Stronglight:
Inside surface of 48 ring to mid tooth of 36 ring = 5mm
Inside surface of 36 ring to mid tooth of 26 ring = 6mm
KMC X10 = ~5.5mm

Biggsy, cheers. I'll look at FD movement.  The fact that the chain can obviously jam, if only in certain less common sprocket-rings combos worries me a bit.
edit. Up and down the road with 'normal' shifting behaviour, it seems OK.  FD 5703 seems to be working reasonably well (ATM).

[Brucey]

if you compare the two photos on this page

http://www.spacycles.co.uk/m2b0s109p3051/SPA-CYCLES-TD-2-Touring-Cranks

you can clearly see the mounting pads on the black triple cranks for the small chainring. However I don't recall if there are also spacers there or not (I've seen with and without on various different chainsets). It is easy enough to find out though.

I would not ride a setup where the chain could drop down like that; sod's law says that it will be down there like a rat down a drainpipe and get jammed at the least convenient time.

Some options;

- thinner spacers (if you have spacers)
- machine the crank mounting pads down
- space the middle ring leftwards using thin washers (they are sold for this exact purpose) but only if this then doesn't increase the middle to big spacing too much....
- revise/replace the inner chainring

cheers

[Ian H]

Interesting.  I have the RD-2 triple.  Like yours the inner ring bolts directly to the spider.  Just looking I can't see any spacers.  10-speed works fine.

The TD-2 has a smaller BCD for the outer rings.  Can't see what the inner is.  But it should be made to the same basic spec.  Perhaps give Spa a ring.  They're generally helpful.

[mzjo]

This has been known to happen with my out of the box Spa triple running 8sp. I just make sure I don't change down at the last minute and that I am very positive with the lever. It can also happen with a second set of Spa triple cranks that are set up as double with the big ring position left empty (I think that the rings are Shimano on those).

[andyoxon]

Thanks for the replies.  Some more rough measurements:

1988-92 Campag Victory triple (zero pins/ramps) previously on this bike
'middle ring to mid tooth inner ring' gap:   = ~5.5mm    Old 8 spd chain = ~6mm

So the gap is a fraction narrower than the new TD-2's ~6mm mid-inner ring gap. 

I suppose then it's the size of the chain ring teeth that really make a X spd-compatible chain chainset?  But I wonder if technically a 'compatible' chainset should by definition have rings gaps smaller than the width of the chain; although it seems perhaps actually there's potential (?) even for a chain which is slightly wider than the ring gap to get jammed, on straight sided rings...

I could ask 'an available workshop' about taking, say, exactly 1.5mm off each 'pad' - and see if that's within their expertise.  Not sure I want to do this though.

It may be that the chain 'never jams again', though I need to weigh whether the 'rat up a drain pipe' scenario looms large enough.

I like the idea of using a square tapered BB set-up, rather than Shimano HT2, but perhaps I should rethink...

[Brucey]

if you look at some triple chainsets they have a large gap between the ring centres but they play tricks such as

- adding shoulders to the larger ring of a given pair
- adding offset chamfers to the tops of the teeth on the smaller ring

and so forth, in order to prevent the jamming issue.

BTW you say your chain is ~5.5mm. That seems a bit skinny for a 10s chain; IIRC they are usually ~5.85mm wide...? Is it perhaps an 11s chain?

Also if you do start to rework parts it might be easiest to machine/enlarge the counterbores in the small chainring so that the mounting pads can go into them. Or file the OD of the pads down so that they can fit into the existing/new chainring counterbores.

BTW the spacing of the chainring centres must usually exceed the chain width by a certain amount, simply because the chain has to run at an angle past the larger chainrings when using small-small gearing combinations. This means that it is possible to overdo it if you start machining stuff. Fortunately this can always be corrected by using shims if needs be.

cheers

[andyoxon]

OK thanks, 5.85mm - my measurement of the KMC X10 was not really accurate enough.

Had a bit of a test ride, and front / rear derailleurs are working nicely. However I have pinpointed one set of conditions which seems to reproducibly cause jamming.  With the chain on rear sprockets 5-10, and middle chain ring, shifting from mid to small ring seems OK.  Once the chain is on rear sprockets 4 or less and mid ring, shifting to the small chain ring - say by accident (going small ring instead of big), pushes the chain only as far as over the gap between the rings and is then pulled down into the gap.  The only way I could release the chain was to loosen the small ring.  I think probably the risk of jamming is too great.  I've ruled out 'machining' anything really.

[Smeth]

Been plagued with the same issue and same chainset with chair  slipping into both gaps especially with a bit of cross on the chain e.g. small sprocket changing down to middle ring. A friend has the same and considered placing a rivet strategically. In the end I found Campage Athena 11 speed triple chainset for a reasonable price with closer rings and vastly better shifting. The rings are closer but still a lot further apart than 10 speed Shimano sprockets so no probs.

Sent from my SM-J510FN using Tapatalk

[Brucey]

.....  I think probably the risk of jamming is too great. .....

I agree.

....I've ruled out 'machining' anything really.

don't shoot the messenger here, but it may boil down to a choice between that and a different chainset...?

cheers

[trekker12]

I had a similar problem with an Xd-2 triple and kmc 10 speed chain. I know it's a different chain set but there seems to be similarities. The chain dropped between the rings and didn't pick up on the next ring. In my case this was when shifting from middle to top.

I could kind of make it work but didn't want to rely on it on tour so gave up and bought a tiagra chainset which has much more detail in the way of ramps and pins which clearly prevent the chain stopping between the rings.

The spa design might work on a wider chain but on 10 speed it doesn't seem suitable.

[mrcharly-YHT]

Or the bodger's delight option. Drill some holes in those chainrings and add some thicker rivets. Just stainless screws would work
If you had access to a pop riveter I guess pop rivets would also work.

[trekker12]

True, that would work.

Although I will say the shifting action on the Tiagra is so much smoother than previously on the Spa set.

[andyoxon]

Thanks all.  I'm kind of committed to 10 spd now, so what are my options for new (or available)...

10 spd square taper triple chainsets...  OR

Shimano 10 spd + Hollowtech2.  I note that the 105 5703 triple HT2 bottom brackets aren't even made any more, is there a new / compatible option?

[zigzag]

all shimano hollowtech2 road bottom brackets are cross-compatible, new or old

[Ivo]

I had a similar problem with an Xd-2 triple and kmc 10 speed chain. I know it's a different chain set but there seems to be similarities. The chain dropped between the rings and didn't pick up on the next ring. In my case this was when shifting from middle to top.

I could kind of make it work but didn't want to rely on it on tour so gave up and bought a tiagra chainset which has much more detail in the way of ramps and pins which clearly prevent the chain stopping between the rings.

The spa design might work on a wider chain but on 10 speed it doesn't seem suitable.

I have the same issue with a Stronglight crankset (triple) and again a KMC 10 speed chain. Since all three of us use thsi chain, we might have a suspect.
I'll replace the chain anyway before LEL so i guess it won't be a KMC .

[andyoxon]

I had a similar problem with an Xd-2 triple and kmc 10 speed chain. I know it's a different chain set but there seems to be similarities. The chain dropped between the rings and didn't pick up on the next ring. In my case this was when shifting from middle to top.

I could kind of make it work but didn't want to rely on it on tour so gave up and bought a tiagra chainset which has much more detail in the way of ramps and pins which clearly prevent the chain stopping between the rings.

The spa design might work on a wider chain but on 10 speed it doesn't seem suitable.

I have the same issue with a Stronglight crankset (triple) and again a KMC 10 speed chain. Since all three of us use thsi chain, we might have a suspect.
I'll replace the chain anyway before LEL so i guess it won't be a KMC .

If there are 10 speed chains wider than ~5.9mm that would be interesting.  I couldn't seem to find any.  edit.  apparently the SRAM PC-1051 10 speed is 5.95mm.  I tend to suspect the chainset.

[andyoxon]

all shimano hollowtech2 road bottom brackets are cross-compatible, new or old

Thanks, am I right in thinking that the spacer required for a triple HT2 chainset comes with the cranks rather than the BB?

[zigzag]

yes, the spacer comes with the chainset