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Trying to fit chain watcher on 6-4 Ti gravel bike
 

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Nick Payne
Joined: 10 Jan 2004
Posts: 2332
Location: Canberra, Australia

3/25/18 9:21 PM

Trying to fit chain watcher on 6-4 Ti gravel bike

I've been building up a gravel bike using a Lynskey Gr Pro frame - the one that has triangular top tube and down tube. One thing I haven't been able to sort out is how to fit a chain watcher. I'm using 38/26 chainrings and a clamp-on MTB FD.

The Deda dog fangs that I normally use can't be fitted low enough because the junction of the seat tube and triangular down tube is considerably higher than on a frame with round tubes - too high for the 26t chainring. Ditto for one of the Jump Stop chain watchers. If I went to an FD designed for a braze-on fitting, together with with the adapter for fitting it to a frame without the braze-on, then there is a form of chain watcher that mounts to the bolt holding the FD to the adapter - K-Edge make one, for example - and that would work. Except that braze-on MTB FDs don't exist, and all the road FDs I've tried have too long a cage to be used with a 38t big chainring - either the bottom of the derailleur cage fouls the chainstay, or if you raise the FD high enough for that not to happen, it's so high above the chainring that it does an absolutely crap job of shifting to the big ring. Any suggestions?

<a href='https://photos.google.com/share/AF1QipNcmFr3TsQzDY0QWnhIl5-E03ZKdc6i2st9M1pUGka5oFimkri1PTBmX0nLCgbgmA?key=M25sczB1NkNwU09XckZ6Qm9PcUZxZHFkb3Z1blJ3&source=ctrlq.org'><img src='https://lh3.googleusercontent.com/nhFlAqFVXL-yP9wLOD4FoGnB420-8COXTey7TCDY6jbe1vBKfHC9zm_I7lSt9nd5-2N5dAbNqCmsxpWh1GTO1hxGLIIs59Fqx-SGnqb8tASOwOEFrvnCjtDilWr_LRfoSy3hEyMy1g=w900' /></a>

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Sparky
Joined: 08 Dec 2003
Posts: 16242
Location: Portland, OR

3/25/18 10:11 PM

Consider an E-type Shimano front DR? I have two, one with 22/32/44 triple and one with 28/40, the E bracket is a chain watch basically. Works with bar cons of MTB shifters.

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daddy-o
Joined: 12 Apr 2004
Posts: 3013
Location: Springfield

3/25/18 10:19 PM

The Lynskey site has a "chat with a Lynskey expert" feature.

It's almost like you need something held in place by the fixed cup.

Can you even see the valley between the teeth, looking perpendicularly from the DT/ST joint?

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Nick Payne
Joined: 10 Jan 2004
Posts: 2332
Location: Canberra, Australia

3/26/18 3:40 AM

@Sparky - I don't think I can use an E-type FD: the cranks are mounted on a 107mm BB to get correct chainline, and adding the 3mm (approx) thickness of the mounting plate for the E-type would throw the chainline off a fair bit, plus I think it would result in the inside of the NDS crank fouling the flange of the BB cup on that side - you can see from the image I posted that the inside of the crankarm there is already extremely close. For the same reason I don't think I could switch to a shorter BB to get the chainline correct with an E-type FD.

@daddy-o - the top of the teeth on the small chainring are actually below the DT/ST junction when viewed horizontally.

I'll just run it without a chain watcher and see whether I get any dropped chains...

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Brian Nystrom
Joined: 26 Jan 2004
Posts: 3956
Location: Nashua, NH

3/26/18 5:48 AM

Make one that's molded to the frame

I did this on the downtube of my Supersix Himod, but you could do it on the seat tube or the junction area.

1- Cover the area of the frame closest to the chainring with masking tape. Make sure it's smooth.

2- Apply JB Weld over the tape and build it up to roughly the shape you want, leaving a bit extra.

3- After it cures, sand/grind it to shape.

4- Carefully pry/peel your new chain watcher off the the frame.

5- Remove the masking tape from the JB Weld.

6- Apply double-sided tape to the mounting surface

7-Clean the frame with a good solvent, then apply the chain watcher.

I did this several years ago and it's still working great.

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Sparky
Joined: 08 Dec 2003
Posts: 16242
Location: Portland, OR

3/26/18 9:59 AM

Isn't the 'Third Eye' band flexible enough to follow any shape seat tube?

Getting one with the right diameter is another thing I guess.

But hybrid idea, cut it and double sided tape it into place.
I like Brian's idea too.

My other question is, why on the DT, the few I have all are on the seat tube, which appears round on yours.

I have a few Third Eye and Token TK375 types in use.

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Brian Nystrom
Joined: 26 Jan 2004
Posts: 3956
Location: Nashua, NH

3/26/18 12:45 PM

I should have specified...

...that I have a Third Eye on the seat tube, too. ST-mounted chain watchers do a good job of preventing shifting-related chain drops, but...

The reason for a chain watcher on the downtube is simple, but it's something that I think that most riders aren't aware of: Many dropped chains don't come off at the front derailleur, they come off at the bottom of the inner chainring. This is especially true on bikes that are used off-road and get bounced around, which is why I mentioned it to Nick. A chain watcher on the DT can keep the chain from coming off completely, allowing you to pedal to get it back on. Ideally, bikes would have a chain watcher at the 6:00 position on the BB to eliminate the problem at the source, but there's no convenient tube there. There are MTB chainguards that do that, but they either mount under the BB cup or require special mounts on the frame.

Another issue is that a chain that comes off completely can get jammed between the crank spider or chainrings, and the bottom bracket. IIRC, this is the main issue I had with the Supersix (though it's been so long that I don't really remember). The DT chain watcher that I installed on it has its share of scars, so I know it's working.

The mounting method I chose has lots of surface area at the tube, so it holds really well, but I can remove it if I ever want to or if I need to replace it.

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Sparky
Joined: 08 Dec 2003
Posts: 16242
Location: Portland, OR

3/26/18 1:59 PM

Brian, so it is kinda of like the rear glued on chainstay chain suck protectors then? My Madone and Domane have a Gorilla Tape patch on the DT in case, and the Trek have a built in drop stop that is well designed and implemented IMO.

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Brian Nystrom
Joined: 26 Jan 2004
Posts: 3956
Location: Nashua, NH

3/26/18 3:22 PM

I'm familiar with anti-chainsuck chainstay protectors...

...and the Supersix has one, but I'm not familiar with the Trek drop stop. What I installed is on the downtube, between it and the teeth on the 34T chainring. It prevents the chain from dropping down between the downtube and the chainring.

This arrangement on a Focus Mares may be the ultimate in chain retention for 'cross/gravel bikes:



If I'm not mistaken, it wraps around and almost touches the front derailleur cage.

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Nick Payne
Joined: 10 Jan 2004
Posts: 2332
Location: Canberra, Australia

4/17/18 2:00 AM

Well, I've had the bike on quite a number of rides, including several with a mixture of unsealed roads and fire trails, and no problems so far with the chain dropping. So it seems to be ok without a chain watcher. The inner side of the derailleur cage is quite deep - the bottom of it is only about 3mm above the teeth of the small chainring, this can just be seen in the 2nd photo - and probably serves much the same purpose:

<a href='https://photos.google.com/share/AF1QipNxiawK3d6bC-kdNOHz-5jRm8adSdRUpUkLjn6DLuhHNO1r-Uwz0K1fZ7iOKR8QHQ?key=TmFqVnBEQ29OS05tWVByR2ZUZ0h5cjNQekxGR1BR&source=ctrlq.org'><img src='https://lh3.googleusercontent.com/XYThLD3AtjlTtVPFBtzJ4smsBbi_aWmgV1MQrnpaU5ZVRkDRa9xxhd_RM-ZLTHqjuaKEWzVIWTEvDSNOFymnvdWVR3fqSuWSoN-6kY509wswJ79wmPAQjWl9qTvuFj1Rce0u-9SXsA=w1200' /></a>

<a href='https://photos.google.com/share/AF1QipMXh-BYR-yuxuVf6h1wUdcG1FkmSZ5kOYTbqaEn0BpDbs8tKh42gxf8je9wUo53sA?key=d0ViejRzUGQtb2xoZFJLVGNPMHB3MWRvT3VSdWJR&source=ctrlq.org'><img src='https://lh3.googleusercontent.com/TQDv3MawfwV50LtR-Rre-7S9j29qePDJDkdX6kO-foXK6vcKV6qaicswTpYUZyEjGPUGfx68OBol6q6WYeq8hBDQZdJdfyNddpUAAdJ7vNar8lcTVAEk2Fq-Ke2HGp3UqwXBmMDMoQ=w1200' /></a>

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