Author Topic: Chainglider on Mk 3 Mercury  (Read 4788 times)

JohnR

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Chainglider on Mk 3 Mercury
« on: November 01, 2020, 04:41:50 PM »
I've now succeeded in fitting a Chainglider to my Mk 3 Mercury. I first tried last weekend but discovered for myself, despite much reading in this forum, that Chaingliders and Thorn chainrings don't happly coexist due to the thickness of the latter. 42T 104 BCD steel chainrings aren't the easiest things to find. After much searching of the interweb I found this https://www.sourcebmx.com/products/jet-bmx-4-bolt-race-chainring?currency=gbp . I then satisfied myself using some mathematics to determine if a steel chainring of that size and indicated weight would be no more than 3mm thick and placed an order. The chainring arrived and the thickness is 2.5mm. The teeth are slightly offset (see photo) and the tooth centreline is about 1mm from the flat surface. However, the chainring didn't want to sit comfortably on the spider and I had to cautiously file some material off the ends of the chainring arms. The bolt holes lined up perfectly. That done the chainring fitted snugly and, based on the variation (or lack therof) in chain tension when cranks are rotated, seems to be close to round.

Fitting the Chainglider was then fairly straightforward. I had to trim about 2cm off the back end of the front parts of the casing and chop a bit out of the rear sprocket cover where it conflicted with the seatstay (hole now covered with some black tape). I've been out on a couple of short rides and any resistance due to the Chainglider is negligible compared to that provided by the current windy conditions. There must be a little friction as the cranks no longer rotate when I push the bicycle forwards (a benefit, IMO). As I also fitted a new chain (KMC E1), I plan to take the Chainglider off in a week or two to check for any initial chain stretch and will then leave it in place until the spring when I'll have to decide if it comes off for the summer half of the year.

As the new chainwheel is thinner than the old one then I needed to shift the cranks about 2mm to the right to try to maintain Herr Rohloff's required 57mm chainline (not the easiest thing to measure accurately) . The one remaining project, for now, is to cut a side off four 2mm thick washers which fit the crank bolts so I can put these in as spacers between chainring and spider so I can get the cranks back to a more central position (not that my legs noticed the rightwards shift).

Andre Jute

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Re: Chainglider on Mk 3 Mercury
« Reply #1 on: November 02, 2020, 10:57:06 AM »
Very professional job!

You might consider running the Chainglider year round. It does a good job of keeping dust off the chain, to the extent that I run my chains for their entire service life on the factory lube. Jobst Brandt, a distinguished bicyclist and component innovator
https://en.wikipedia.org/wiki/Jobst_Brandt
used to say that grinding paste was just dust and oil.

JohnR

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Re: Chainglider on Mk 3 Mercury
« Reply #2 on: November 03, 2020, 10:23:05 PM »
I think the professional appearance of the Chainglider installation can be ascribed to Hebie's design. For me, the challenging part of the exercise was finding the 42T 104 BCD steel chainring.

Anyway, I tried fitting the steel washer spacers today but they ended up making the bolts too short so I abandoned that plan (something doesn't add up: 2.5mm thick chainring + 2mm thick washer = 4.5mm which is thinner than the 5mm thick Thorn chainring). Instead I rechecked the chainline. For the standard 135mm OLD hub this is 55mm or 57mm depending on the sprocket carrier https://www.rohloff.de/en/experience/technology-in-detail/specifications. So I next measured the hub and sprocket and found that it's 60mm between the outside of the spoke flanges and 25mm from outside of the flange to centreline of the sprocket, ie chainline = 60/2 + 25 = 55mm. I then adjusted the bottom bracket for the 55mm chainline (27.5mm from the centre of the O in Thorn) which put the cranks very close to central (ie same distance each side between back of crank and frame). Mr. Thorn's workshop seems to have selected the right parts but the ability to slide the EBB laterally in the frame is a mixed blessing.

If the Chainglider continues to run as freely as it currently appears to then I see no reason to remove it. The transmission losses due to Chainglider + clean chain could well be less than those caused by a filthy chain. I've previously been down the Gates Carbon Belt route (the bike is still at the back of the garage) and suspect that it's worse in terms of transmission losses and I know that a dirty belt makes various disconcerting noises.

steve216c

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Re: Chainglider on Mk 3 Mercury
« Reply #3 on: November 05, 2020, 03:31:08 PM »
John,

I too just fitted a chainglider 3 weeks back on a non-Thorn Rohloff bike. To be honest with you I was skeptical, but almost 500km in and I am now a full convert. We've had some miserable wet weather since I fitted, and I've been on muddy trails, through deep puddles and covered in soggy leaves kicking up from the asphalt, and the chainglider is keeping the chain free of all that crud.
I was a bit worried that it had a bit of play, but it seems to just sit there and do what it should. I only notice it when 'reversing' my bike out of the shed on a morning, but once riding in a forward direction it is a true fit and forget upgrade.
I'm running a dipped in hot candle wax chain as I was fed up with oily trouser legs prior to the chainglider. It remains to be seen how the wax stays on chain long term with the Hebie. I may need to switch back to chain grease or oil if the wax stops lubing. But at least under the chainglider it will stop the traditional lube getting dirty and ineffective.

Good luck!
Steve



If only my bike shed were bigger on the inside...

JohnR

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Re: Chainglider on Mk 3 Mercury
« Reply #4 on: November 07, 2020, 06:11:56 PM »
A few days ago I put the bike on my maintenance stand so I could do some fine tuning on the Chainglider by moving the rear part back /forwards a click at a time on the top / bottom arms to find the sweet spot where there was least obvious drag between chain and Chainglider when gently rotating the pedals forward (it was more a case of finding the mid-point between positions where the chain was rubbing on something). Anyway, it's running very smoothly and any extra resistance is negligible compared to a bit of wind. I must make some marks on the arms to designate this optimum position in case I need to remove the Chainglider.

The remaining unknown to me is whether my 42T chainglider would be happy if I fit a slightly smaller (41T, possibly 40T) chainring should I want slightly lower gearing to offset fitting a slightly fatter tyre. I think that going to 38T (the next size option) is too much. If no one has the answer to this I'll have to ask Hebie.

Andre Jute

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Re: Chainglider on Mk 3 Mercury
« Reply #5 on: November 07, 2020, 09:04:23 PM »
The remaining unknown to me is whether my 42T chainglider would be happy if I fit a slightly smaller (41T, possibly 40T) chainring should I want slightly lower gearing to offset fitting a slightly fatter tyre. I think that going to 38T (the next size option) is too much. If no one has the answer to this I'll have to ask Hebie.

Yes, we know the answer to that one. Hebie's Chainglider fits the chainrings they declare it fits and the sprockets by hub manufacturer plus tooth count that they declare it fits, and no others. You can see why by calculating the diameter of each tooth count of chainring. The Chainglider works by being close-fitting. If there is a gap, dirt will get in and it won't work, in fact, it might work adversely by pressing the dirt that enters against parts of the gears and chain that should be clean and free-running. Though we know for a certainty, because someone tried it, that a 36T chainring in a 38T Chainglider just doesn't work. I can't tell with certainty whether you will get away with using a 41 tooth chainring with a 42T Chainglider, so you might wish to cut a cardboard circle to the 41T diameter and just hold it up to the components still on the bike to see how much "empty space" there is.
« Last Edit: November 09, 2020, 10:20:31 AM by Andre Jute »

martinf

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Re: Chainglider on Mk 3 Mercury
« Reply #6 on: November 08, 2020, 08:17:14 AM »
If you haven't already got the largest recommended sprocket for your Chainglider, increasing sprocket size could be a way of lowering the gearing.

AFAIK the current model Chainglider rear part for Rohloff will work with 15, 16 and 17 tooth sprockets.

Andre Jute

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Re: Chainglider on Mk 3 Mercury
« Reply #7 on: November 08, 2020, 09:17:11 AM »
1. The forum member who tried running a 36T chainring in a 38T Chainglider is Frank Revelo. The link to his photograph is
http://www.thorncycles.co.uk/topic=4412.msg32313#msg32313
but it it merely calls up a dead-end notice; it seems likely that the photograph and the discussion about it is gone for good. [EDIT: Dan the Man has restored Frank Revelo's post and the photograph and you can see both here:
http://thorncyclesforum.co.uk/index.php?topic=4412.msg32313#msg32313
and you can also see John Saxby's neat surgical solution to the problem in his post below.]

2. I found this text, by me, which I'd forgotten about:
"On your other problem, of whether 38T Chainglider will fit a 36 chainring, I'm now doubtful. Try this. Calculate the diameter of a 36, 38, 42 and 44 tooth chain wheel, which is roughly 6, 6.33, 7 and 7.33in. If the 44T Chainglider would fit the 42T chainring, why did Hebie make a 42T front end as well? The actual difference from 38T to 36T is the same as from 44T to 42T, a third of an inch, about 8mm."
http://thorncyclesforum.co.uk/index.php?topic=2233.0
I'm afraid the calculation and Frank Revelo's experience dashes hope of the mismatched Chainglider working any better for you.

3. There's still the possibility of swapping sprockets, which Martin outlines above.
« Last Edit: November 09, 2020, 09:58:38 AM by Andre Jute »

JohnR

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Re: Chainglider on Mk 3 Mercury
« Reply #8 on: November 08, 2020, 07:00:28 PM »
Thanks for the suggestions and info. I'm already using the 17T sprocket so increasing that isn't an option, besides which a 1T change on the sprocket has a much bigger impact on the gearing than 1T on the chainring. The attached photo shows the Thorn 41T chainring in front of the 42T Chainglider. It's lined up at the bottom (that's how I could hold it in position) but, in reality, the potential gap is at the top. Theory says the 1T difference in diameter between 41T and 42T is about 4mm so the teeth of the 41T should be just about inside the Chainglider. I suspect that 40T would leave part of the teeth exposed which becomes an entry point for muck (a risk compounded by being at the bottom).

Before the Chainglider I was running on 41T + 17T. This has become 42T + 17T to suit the Chainglider and has increased the gearing by 2.4%. I thought this would be offset by changing the Schwalbe nominally 50mm G-one speed tyres to the nominally 48mm Panaracers but the difference in actual circumference is much less than expected. I'm OK at the moment but was considering other Schwalbe tyres with a bit more tread than the G-one tyres which came on the bike and most of these seem to be 54mm or larger. However, I see that Schwalbe now show a 50-584 version of the G-one bite https://www.schwalbe.com/en/tour-reader/schwalbe-g-one-bite which doesn't seem to have reached UK sellers yet. I don't know if that's actually a new tyre or means that the current 54-584 was actually undersized and is being relabelled. It could be the latter.

A fall-back would be to change to 38T + 16T which gives about 4% lower gearing than 42T + 17T. However, this involves buying chainring + sprocket + front half of Chainglider compared with which buying and trying a 41T chainring with the 42T Chainglider is a cheap experiment. In reality a few percent in the gearing is splitting hairs but the differences can add up. At the moment I've got the bottom two gears on my Rohloff in reserve for heavy loads, abnormal hills (my steepest local hill is about 15%) or feeling knackered. Given the impending shambles called Brexit and possible implications for the supply of bike parts I want to build up my stocks of anything needed in the forseeable future.

John Saxby

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Re: Chainglider on Mk 3 Mercury
« Reply #9 on: November 08, 2020, 11:20:31 PM »
Here's a (the?) mysterious source of the story of a 38T 'glider mated to a 36T ring:  'tis me wot done it, sir! I did it ages back--surgically adapted me 38T 'glider to a 36T ring.  Did it in August 2015 I did, and all these years later, it's still working.

Here's the story and the foto:

1)   First, attached below is the foto of the violence surgical adaptation done to the 'glider.  You'll see that the part covering the rear of the chainring has been removed.  I could've left it intact, but the curvature of the 'glider would've been mismatched with that of the smaller ring, and I found that jarring to my sense of visual symmetry.

2)   Why did I order a 38T 'glider when I had a 36T ring, you ask?  I didn't:  I started with a 17 x 38 setup on my Raven, and after a season and a half, decided to lower my gearing to 17 x 36.  This has worked very well for me.  The summer after the change (2016), I did a 2400 km trip in the Rocky Mtns and Cascadia, and the new gearing did the business.

3)   Consequences of the fit of a smaller ring, and the surgical change?  WRT the smaller ring, there's more play (I often use the word "slop"), both fore-and-aft and up-and-down.  I sometimes run the bike sans 'glider, and honestly, I can't tell the difference betw the "with" and the "without".  (Then again, maybe a bloke that uses a word like "slop" isn't a good judge anyway.)

   WRT to dirt, nothing extra that I can see.  The only place I ever see any slight buildup of oily crud is on the entry and exit "gates" of the rear part of the 'glider where it embraces the rear sprocket. I clean that away once or twice a year, and I did that before I changed the size of the ring and made the adaptation to the 'glider.  I don't ride a lot in the rain, but I do ride about 10% of my distance on rural gravel.

4)    There's more surgery, however, that you can't see.  This is subtle, but in my opinion, it's at least as good as the surgical adaptation you can see.  The 'ring you see in the photo is a Surly stainless item.  I have used three of these, the 38T item which was the original, dating from spring 2014; and two 36T rings, which I used until 2018.  Then, I ran into problems with new stainless rings being both oval and out-of-plane, so I was getting a major tight spot and a variable chainline with two successive new rings.

       I decided to switch away from the very durable stainless rings to a beautiful alloy item made by Origin8 and sold by Rivendell Bike Works.  This is fractionally thicker than the Surly stainless ring, but is perfectly round and flat.  Its toothed section is, however, 3mm thick, and this is the max recommended by Hebie.

       So, I did another surgical adaptation on the remaining part of the 'glider which touched the new ring, thus: On the inner part of the 'glider where it touches the front, top and bottom of the chainring, there's a small collar of plastic, about 1 mm in size, on both inner and outer parts of the 'glider.  I carefully removed that with an exacto knife and file, and -- voilá! -- more slop play right where I needed it.  My precious alloy ring doesn't get squished/polished by my equally precious adapted 'glider.  Each remains at a suitable mechanical distance from the other, a very COVIDian fix that predates 2020  (Dunno what the collar did -- add some rigidity, perhaps?)

So there we are:  my bit of heresy seems to have brought me no mechanical misfortune, so far at least.
« Last Edit: November 08, 2020, 11:23:22 PM by John Saxby »

Andre Jute

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Re: Chainglider on Mk 3 Mercury
« Reply #10 on: November 09, 2020, 12:03:49 AM »
Here's a (the?) mysterious source of the story of a 38T 'glider mated to a 36T ring:  'tis me wot done it, sir! I did it ages back--surgically adapted me 38T 'glider to a 36T ring.  Did it in August 2015 I did, and all these years later, it's still working.

Very neat job, too, John. and a good description of how to do it. I imagine the little crossbar you exacto'd out is a stiffening rib, probably for our purposes German overkill design because the Chainglider is very sturdy indeed even just from the pure heft of hardwearing material.

***

What I was talking about, and what put the rest of us off even trying it, were Frank Revelo's misadventures, where there was an ugly gap between the top of the teeth on the chainring and the inner side of the Chainglider around about a third of the circumference. But Frank's photograph, taken before he threw the Chainglider away, is gone, probably for good, because even Dan's helpful reference to it a few years ago leads only to a notice that the page can't be found.

EDIT: Dan the Man has restored Frank Revelo's post and the photograph and you can see both here:
http://thorncyclesforum.co.uk/index.php?topic=4412.msg32313#msg32313
and you can also see John Saxby's neat surgical solution to the problem in his post immediately above.
« Last Edit: November 09, 2020, 09:55:05 AM by Andre Jute »

JimK

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Re: Chainglider on Mk 3 Mercury
« Reply #11 on: November 09, 2020, 05:25:52 AM »

Danneaux

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Re: Chainglider on Mk 3 Mercury
« Reply #12 on: November 09, 2020, 06:09:59 AM »
Quote
...there was an ugly gap between the top of the teeth on the chainring and the inner side of the Chainglider around about a third of the circumference. But Frank's photograph, taken before he threw the Chainglider away, is gone, probably for good, because even Dan's helpful reference to it a few years ago leads only to a notice that the page can't be found.
Check here, Andre...
http://thorncyclesforum.co.uk/index.php?topic=4412.msg32313#msg32313

The domain name used for indexing some old posts changed when the Forum domain was renamed several years ago. You can still access old posts if you update them to prepend the proper root URL. I have been converting all such entries but as you can imagine, it is a time-consuming task.  ;)

All the best,

Dan.

Andre Jute

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Re: Chainglider on Mk 3 Mercury
« Reply #13 on: November 09, 2020, 09:48:13 AM »
Revelo does have a photo at: https://www.frankrevelo.com/hiking/biking_nomad2012.htm

Thanks, Jim. That article is well worth a read for any tourer as a template for specifying a touring bike and its accoutrements.

Quote
...there was an ugly gap between the top of the teeth on the chainring and the inner side of the Chainglider around about a third of the circumference. But Frank's photograph, taken before he threw the Chainglider away, is gone, probably for good, because even Dan's helpful reference to it a few years ago leads only to a notice that the page can't be found.
Check here, Andre...
http://thorncyclesforum.co.uk/index.php?topic=4412.msg32313#msg32313

You're a lifesaver, Dan.

The domain name used for indexing some old posts changed when the Forum domain was renamed several years ago. You can still access old posts if you update them to prepend the proper root URL. I have been converting all such entries but as you can imagine, it is a time-consuming task.  ;)


I thought it was something like that but didn't want to ask, precisely because I know from contemplating restoring my old blog to the net how much tedious work it is. Thanks again, Dan.

John Saxby

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Re: Chainglider on Mk 3 Mercury
« Reply #14 on: November 09, 2020, 05:53:59 PM »
Dan, wow!  This is a mix of e-archaeology and magicking!