Domane +HP Chain Drop

[Gar01821]

Hi, I have had my Domane +HP for a year and love it except it has dropped the chain off the front Praxis crank 3 times. When this happens the chain is stuck and crank must removed to free up the chain. Apparently this is a well know issues with the Specialized Creo and the Praxis crank. Any suggestions for a fix?

 

[Deacon Blues]

Have you checked for chain stretch?

 

[Gar01821]

Yes, it was fine but I replaced the anyway and it happened a 2nd time shortly after the new chain. I put the GRX chain tensioner on and it's been fine since but I am still looking for a known solution.

 

[tegnamo]

Did you double check that the chain is indexed properly on the front ring? It's not a true narrow-wide but there is a little graphic on the backside of the ring that shows where the wide links/narrow links need to be aligned w/respect to the chainring teeth. Might help!

 

[Gar01821]

I just read about that on the Praxis website. I do not know how mine is set up, but will check it out tomorrow and let you know. Thanks

 

[Tyson]

You have the known solution. You must keep the GRX rear derailleur clutch on. The only time you turn it off is to remove the rear wheel and maybe when cleaning the derailleur. And you have to remember to turn it back on.

I only forgot once to turn it back on, and I dropped the chain from a bump on a paved road surface. Fortunately it dropped off the outside so it didn't get jammed against the frame, but since there is no front cage it drops all the way off and a lot of chain drags on the ground and this could be very dangerous. I use this bike as a gravel bike too with a second set of wheels. I ride over all kinds of bumps and ruts and it has never dropped the chain.

1. Make sure the chain is properly indexed on the front chain ring. There is a diagram on the inside of the chainring. It can go on both ways, the right way and the wrong way.
2. Always engage the clutch.
3. Keep your chain clean and well lubricated.
4. Periodically check for chain wear, or chain stretch as it is called
5. Make sure you replace the chain with the correct number of links.

 

[Gar01821]

Hay Thanks for the solution. I did everything you advised except I have not insured that the chain is properly indexed, I did not know that was a thing to do. I believe I know how index the chain and will do tomorrow before I ride. Thanks again. BTW, I also use the bike as a gravel bike and have changed my tires to 40mm. Why did you need a 2nd set of wheels?

 

[Tyson]

Hay Thanks for the solution. I did everything you advised except I have not insured that the chain is properly indexed, I did not know that was a thing to do. I believe I know how index the chain and will do tomorrow before I ride. Thanks again. BTW, I also use the bike as a gravel bike and have changed my tires to 40mm. Why did you need a 2nd set of wheels?

I have a second set of wheels for gravel built to be a little stronger (28 spokes vs 24 and strong rim), and since I run tubeless for both sets to have knobby for off road and road tires for on road without having to swap tires. For gravel I run a 40 in a front and a 35 in the back as the clearance there is lower. I also armored my downtube against rocks thrown up from the front tire (and changed to a gravel bar, converted the kickstand to be more easily removable, and in process to upgrade the rear cluster to 11-46 vs 11-42 for a lower gear)

 

[Gar01821]

To All,
I don't know how my chain was indexed in the past when it came off. However, when I just checked today the chain was currently properly indexed on the front chain ring. Thanks for your help.

 

[Tyson]

Well ... I was full of advise on what to do to avoid the chain drop, and my Domane+ HP today dropped its chain and got sucked in. Had to walk out on a dirt trail and call for a ride home.

It was a little bumpy but really not bad, and I shifted but shifted poorly. I think I clicked a couple of times to shift to a smaller cog as I was going downhill. I remember it not being smooth but probably more my fault than the equipment. The right combination of wrong must happened and it dropped on the inner side towards the frame and the spider (holding the chainring), not the chainring, is what has the perfectly wrong clearance and sucked the chain in.

I suppose if I unlinked the chain and pulled hard enough I might get it out, but it seems to already have done enough damage to the carbon frame. I don't understand why a frame would be designed like this today such that the gap can't be made small enough such that the chain can't get through, or big enough that it can't get stuck and do damange on its way in.

I have a Part BBT-18 tool on order now to remove the chain ring spider by removing the lock nut (left hand thread). This requires a 36mm wrench, so if you want to use a torque wrench make sure it works with this. BBT-18 has an 8 sided nut at 36mm not 6 sided so a standard 6 point socket won't work. A 12 point socket will work, but park recommends and sells a 36mm crows foot wrench to use if you don't want to just use an adjustable wrench. Other brands of this tool will take a 3/8" or 1/2" square socket head directly. As I might need to carry tools to fix this on a ride, I intend to make an aluminum 36mm flat wrench that I can carry with the BBT-18 (vs a socket wrench) so I preferred this style. Again, this is reversed thread for this nut.

Under the lock ring should be a rubber O-ring some have reported wants to squish out when tightening: This is part number: Bosch O-Ring - BDU4XX - 1270.016.119
As they are cheap, I plan to have this on hand in case a new one goes in better.

The lock ring is: Bosch 1270.014.085 but a new one shouldn't be needed.

I will find out how bad is the damage in a few days when I take this apart. I expect it to make me sad, but not be structural.

 

[Tyson]

I had to re-engineer this chain issue, and this is my story:
I got the tools to remove the crank and took it apart to release the chain. It is more clear now what happens when the chain drops to the inside. The spider that holds the crank can actually grab the chain and suck it up from underneath and wedge it into the carbon frame. With the chain lodged, then as the crank continues to turn the chain starts to grind down the spider. I stopped pedaling almost instantly but with the motor and all it still turned enough to cause damage. You can see the frame damage in the pictures, and you can see the shiny silver parts on the aluminum crank spider where it ground on the chain. The spider isn't mechanically compromised, and you can't see the damage cosmetically when it is assembled so it is fine. The frame, I can just hope this is fine. Before assembly, I protected the frame with 3M automotive paint protection film in case the chain gets in this area again, which I hope won't happen. Why? Because I designed and mounted another ring behind the chainring so it can't drop onto the spider and get sucked in. I mounted the ring with stainless steel screws designed for plastic that go through the existing holes in the center of the chainring mounting bolts. The ring has a bevel to help catch the chain and draw it away from the frame, and is smooth so it doesn't want to grab the chain. This new ring fills the gap so the chain can't fit between it and the frame. My first design is 3d printed. My second version is going to be machined from marine grade plastic designed to be outside in the weather. I have the bike back together and will do some testing by manually moving the chain off to the inside and turn the crank to see what the chain wants to do.

Below you can see the clearance from the new ring to the frame, which is about 1/8"

 

[tegnamo]

Wow! That's really clever

 

[Tyson]

I went for a trail ride this weekend. The chain dropped again, and to the inside the same as I posted above. This time, however, my chain catcher ... well ... caught the chain!

So I was pretty excited that my design did as expected and saved me. Then, I realized, that I need to work on a design for this bike to keep it from dropping, so that is on my mind now.

Below are the pictures.

 

[Gar01821]

Can you make another? I'm sure a few folks would like to buy one.

 

[Tyson]

Can you make another? I'm sure a few folks would like to buy one.

I'm actually working on that. First is to make it out of marine grade HDPE which is resistant to sun and moisture instead of being 3D printed. Second is to change the design so it can be installed without pulling off the crank and chainring spider. Both these efforts are in progress. I will keep this thread updated.

 

[Gar01821]

Thanks!

 

[Tyson]

Update after some time with this chain catcher design:
It worked as I documented above, but when trail riding I would get small stones between this added catcher ring and the frame. Since I put a paint protection film in that area, which is a soft plastic protection sticker, the small stone would want to embed in that and scrape on the 3D printed ring I added. It isn't hurting my frame, but is annoying to clear and makes a scraping sound until cleared. My first thought is to then design some groves in the ring so small rocks could clear themselves. However, this whole thing with now such small clearance makes me nervous, especially as a solution to others who might not install a protection film.

My new thought is a piece to be designed to be mounted to the vertical water bottle cage mounting holes behind the cage, with an arm dropping straight down to a head just above the chainring that will constrain the chain to not jump off. This approach is what every other manufacturer does, except they have a front derailleur mount or some other mount directly into the frame right above the chainring for this device. As the Domane+ HP frame flares out to accomodate the motor in this area, there is no easy way to add a clamp.

My thought on this arm is to make it such that if it accidently got yanked, pulled, kicked, or caught ... that it will break away instead of causing damage to the bottle cage mounts.

I haven't started on this approach, but if any Domane+ HP owners have any thoughts I am interested in feedback.

 

[Tyson]

I mentioned in my post 6 months ago that I would try to design a solution for chain drop that would keep it from dropping rather than my first solution which was to catch the chain when it dropped so it wouldn't get jammed into the frame. I was thinking to have something that came down from, and mounted to, the water bottle cage mount. The first issue I saw with that is that the distance between different frame sizes was quite large, and the support from the mounts would be far away on the larger frame size.

My current design, shown in pictures below, clips in to the torx bolt for the motor mount (into the bolt head where the torx driver goes, no disassembly required). The third point of contact will be to the frame which I plan for adhesive velcro. As I have in my garage both the smallest frame size and the largest, I am trying to make the same design fit both, which I think will insure it will fit all frame sizes.

The pictures below are 3D prints to test geometries and fitment and will continue to get refined. It snaps in very nicely, and is remarkably sturdy ... but I don't know if I ever will have a good test criteria to make sure it works. My chain catcher version I know works, because it has caught the chain and saved me now several times, but has the negatives described in my prior post. The last time is saved me was on a smooth paved road, so I really don't know what triggers my chain drop issue but I am starting to think it is times when my shifting is "sloppy".

I wanted to give an update so people know I am still working on this and do hope to make this available to others.

 

[drodg]

Looks good. I have never experienced a chain drop on my HP I figure it is just a matter of time.

 

[Tyson]

This picture shows the evolution of my clip on chain guard for the 2020/2021 Domane+ HP.

It clips into the motor mount bolt heads (no bolt removal or adjustment required), and the third point of contact is the base of the seat tube where I am using a velcro "Command Strip". This allows the design to be easily removed, and the adhesive attached to the bike to also be easily removed. I have both the 52cm and 60cm frame (smallest and biggest), so the goal is to make the same design work across all frame sizes.

You can see the alignment to the chain is not adjustable, and what I found between the two bikes I am testing that the motor is mounted +/- 1.0 mm and I am targeting roughly 0.5mm tolerances from the guard to the chain. I will either need to make a universal design with a wider chain guard (less likely to help keep the chain on), or create a few different iterations of guard offset from the frame along with a simple measurement tool to determine which one is needed.

I am now going on rides with this installed, but as my chain drop history is about 1 drop every 1,000 miles it will be tough to prove this is working. Also tough to know when the chain event that this is designed to mitigate happens that it doesn't just jam up and break. I don't plan to do extensive design testing trying to get my chain to bounce in different ways. I am just going to start riding with it and periodically look at how it is getting grease marks and chain impact marks.

Next step is to find a better printer filament. Currently this is PLA. I will investigate a black carbon fiber filled nylon filament as an option, and also see what options there are these days to have it commercially printed.