Author Topic: MK3 Raven Twin chain tensioning  (Read 885 times)

HugoC

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MK3 Raven Twin chain tensioning
« on: April 26, 2020, 02:10:39 PM »
Hi,

I received my new MK3 Raven Twin last year and have accumulated just over 3600 kms on mainly smooth paved roads. I've had to adjust the Eccentric Bottom Bracket on a couple of occasions to take up a little bit of slack on the drive chain, and made accompanying adjustments to the timing chain. I've still got plenty of scope for tightening the drive chain but the timing chain is now at its maximum stretch (i.e., the thick part of the Eccentric Bottom Bracket is just about at the 3 o'clock position, and the chain does look a little slack). I've been advised by Thorn that the next step will be to remove a link from the timing chain, and start again. Although this is not a big job it is not something I anticipated having to contemplate having just completed a mere 3600kms on the tandem. Has any one had a similar experience with their MK3 Raven Twin chains?

Thanks & Regards

HugoC

Mike Ayling

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Re: MK3 Raven Twin chain tensioning
« Reply #1 on: May 04, 2020, 06:25:40 AM »
Our Raven Twin is a 2012 moodel and it got to a stage where I had to replace the timing chain which required two standard chains to get the required  length. Certainly just removing a link would be cheaper. I used two 8 speed chains which were not too expensive.

Mike

HugoC

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Re: MK3 Raven Twin chain tensioning
« Reply #2 on: May 07, 2020, 11:56:13 AM »
Thanks for the reply Mike.

For me, having to contemplate removing a link from the timing chain after so few accumulated miles does not reflect well on the design of the bike. Never mind, it's not a huge task in itself and I expect my chain should not need replacing for a good while after shortening. Time will tell.....

ZeroBike

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Re: MK3 Raven Twin chain tensioning
« Reply #3 on: May 07, 2020, 04:32:39 PM »
I dont even know what the timing chain is, I thought these things direct drive, job done.

However have a read of this

http://thorncyclesforum.co.uk/index.php?topic=626.0

I think chain wear is no better than a derailer .. which kind of makes sense... its in constant contact in either system... its the rest of the parts that live longer on a hub geared bike.. or so Im led to believe lol

HugoC

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Re: MK3 Raven Twin chain tensioning
« Reply #4 on: August 16, 2020, 06:07:16 PM »
Just to close this one - I got myself a chain breaker as suggested by Thorn, took out a link & was able to reconnect the chain, adjust the eccentric BB & fit the chain back onto the bike. Works like a dream. Job done!

Aleman

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Re: MK3 Raven Twin chain tensioning
« Reply #5 on: August 18, 2020, 10:32:27 AM »
As a new Raven Twin owner myself, I did think chain stretch was a little bit excessive ... especially considering we've only done around 120 miles on it (A very new Raven twin owner :D ) ... However, There is a page in the Thorn Owners Manual regarding chain tensioning and wear, and it does say
Quote
"With a new chain (and especially a whole new transmission) it does not take long for 40mm of slack to become 60mm of slack but please don't worry ... this situation will improve dramatically with the passing of miles"

I've not got to the point where I need to adjust anything yet ... In fact I'm still adjusting the stem length ... and that is a MUCH more permanent decision :D
« Last Edit: August 19, 2020, 10:49:16 AM by Aleman »

Pavel

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Re: MK3 Raven Twin chain tensioning
« Reply #6 on: August 18, 2020, 08:40:20 PM »
To add my two cents, which doesn't buy much nowadays, the chain life on motorcycles can get severely shortened if the chain is at all too tight when installed.  I mean you can destroy a chain and even the gasket on the transmission inside of 100 miles if you exceed a certain minimum allowance of slack. 

I wonder if a slightly tight chain would show accelerated wear of a more minor sort on a tandem?

I leave my Nomad chain slack, and have to confess that I've never used the eccentric yet in these past 9 years.  I don't put the mileage on as many of you tend to, but still I've only worn out one chain and am on the second now.  (the Rohloff has been transferred to the RST)

I've yet to finish building up the MK2 tandem.  Too many parts I need out of stock, so I'd like to ask all of you to stop, stay locked down inside, until I get my hands on those parts I need.  Thank you.  ;)

Aleman

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Re: MK3 Raven Twin chain tensioning
« Reply #7 on: August 19, 2020, 11:07:09 AM »
To add my two cents, which doesn't buy much nowadays, the chain life on motorcycles can get severely shortened if the chain is at all too tight when installed.  I mean you can destroy a chain and even the gasket on the transmission inside of 100 miles if you exceed a certain minimum allowance of slack. 

I wonder if a slightly tight chain would show accelerated wear of a more minor sort on a tandem?

You may well be on to something here. When I built up my MK2 Raven Twin in July, I actually did split the timing chain short by a link, and when that was fitted, it was crazy tight, with at most 5mm play  :-[ :-[ Luckily SJSC had supplied the chain(s) as one continuous length, so I was able to nick a link, and the pin from the spare to extend it, although it was a PITA putting one link back on the end of the SRAM chain ... I know I could have used a Quick Link but that would then have had 2 quick links adjacent to each other, and I'd only ever want that on an emergency!

One thing I'm thinking of doing for the Raven Twin, is actually using 3 sets of chains and swapping them frequently (say every 500 miles) I used to do this when we got our Dawes tandem 25-30 years ago, and never had any issues with chain stretch or sprocket wear in the 10,000 miles we did on it, before it was moth balled because of children  :'(

@Pavel, I was lucky enough to get my Mk2 in July as part of the "Sell Off" discounts ... They didn't have a Size 5 in stock as a complete box, but Robin offered me a Size 5 Frame and a "box of bits" to build  one up myself ... Sorry If I used up all the spare parts  :-[ :-[
« Last Edit: August 19, 2020, 01:56:16 PM by Aleman »

martinf

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Re: MK3 Raven Twin chain tensioning
« Reply #8 on: August 19, 2020, 01:13:18 PM »
One thing I'm thinking of doing for the Raven Twin, is actually using 3 sets of chains and swapping them frequently (say every 500 miles) I used to do this when we got our Dawes tandem 25-30 years ago, and never had any issues with chain stretch or sprocket wear in the 10,000 miles we did on it, before it was moth balled because of children

I do variations of this with a set of 2 to 4 chains each on nearly all the family bicyles. Using several chains and swapping them regularly is IMO much more economical on chainrings and sprockets than running the transmission with a single chain until everything is worn out.

Intervals for swapping range from 200 kms as worst case on a Brompton in bad weather to over 2000 kms on hub gear bikes with Chaingliders.

I reckon this is more important for a derailleur bike with multiple, often expensive chainrings and sprockets, it is less interesting financially for the bikes with the very cheap Shimano and Sturmey Archer hub gear sprockets (which are often reversible anyway), but IMO even on these the chainring makes it worth doing.

Pavel

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Re: MK3 Raven Twin chain tensioning
« Reply #9 on: August 19, 2020, 03:28:23 PM »
Thus far I'd been a chainglider skeptic but I'm slowly coming around to liking the idea of trying it.  Is there a chainglider product that would fit onto a Tandem?  Tandems seem a good place for going further to extend chains, seeing the double effort, but especially as it would be nice to not worry about the stoker getting grease on the legs, and burning my eggs in camp until I see the light.

martinf

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Re: MK3 Raven Twin chain tensioning
« Reply #10 on: August 19, 2020, 06:58:52 PM »
Is there a chainglider product that would fit onto a Tandem?

Almost certainly not on the (front) timing chain. It might be possible on the (rear) drive chain if:

- the timing chain is on the left side (crossover drive).
- the tandem uses a Rohloff hub.
- the chainring and sprocket sizes are one of the limited combinations that work with a Rohloff-specific Chainglider.

martinf

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Re: MK3 Raven Twin chain tensioning
« Reply #11 on: August 19, 2020, 07:08:30 PM »
If it is compatible with the crankset, sprocket and required gear range constraints, it might be worth trying this KMC wide chainring/chain/sprocket system:

https://www.kmcchain.eu/10000km

Though I doubt if they would guarantee 10,000 kms on a tandem.

Danneaux

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Re: MK3 Raven Twin chain tensioning
« Reply #12 on: August 19, 2020, 08:42:38 PM »
Quote
If it is compatible with the crankset, sprocket and required gear range constraints, it might be worth trying this KMC wide chainring/chain/sprocket system...
As a data point, I am running a 1/8in chain, sprocket, and chainring on my Fixie and found the wider bearing surface has so far reduced chain "stretch" (lengthening due to wear) and the gear teeth are lasting longer as well. Unlike my Nomad's Rohloff sprocket, the Fixie's is heat-treated steel rather than stainless.

A fixed-gear bike (mine, anyway) tends to load the chain not only under drive but also during backpedaling/braking and I didn't find the 3/32in setup to last so long over time despite the straight chainline. It seems Japan's Keirin racers agree; bikes for this high-stakes form of parimutuel betting are setup for high strength and maximum reliability and though light, the bikes are built for stout as muscular riders really hammer away in the closing sprint of each heat. See:
https://en.wikipedia.org/wiki/Keirin
https://www.youtube.com/watch?v=pVK0iwScTvs

My own tandem used 3/32in chainrings and an older 6-sp SunTour indexed freewheel. It gets good service life from the derailleur components as well as the timing chain. The timing chain of course lasts longer because it is a straight run, the same as you would find with an IGH. I set my timing chain up initially for 12.5mm/or a half-inch of slack in the lower run. It has worked well for me after centralizing the two timing chainrings to make sure they were turning as round as could be. My tandem doesn't flex enough to make the chain too tight under high pedaling loads, but this can occasionally be a problem for a strong team on a cheap or lightweight tandem, especially in hilly country.

Best,

Dan.

Pavel

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Re: MK3 Raven Twin chain tensioning
« Reply #13 on: August 20, 2020, 12:37:28 AM »
Is it a better idea. to buy a 1/8th" chain for a tandem versus a 3/32", for longevity purposes?  What about the 1/6 gram weight penalty, I wonder, if going ultra light, versus ultra smart?

Aleman

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Re: MK3 Raven Twin chain tensioning
« Reply #14 on: August 20, 2020, 11:55:17 AM »
Is it a better idea. to buy a 1/8th" chain for a tandem versus a 3/32", for longevity purposes?  What about the 1/6 gram weight penalty, I wonder, if going ultra light, versus ultra smart?
My Mk 2 was supplied with KMC-e 1/2 inch by 3/32 chain. I'm going to stick with that, and see what sort of wear rates I'm getting, before worrying too much about it ... As I said, I may also by a couple more lengths of it to try and minimise wear anyway.