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2008 TW200
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Discussion Starter #1
A couple weeks ago I was cutting up at an OHV park and my chain derailed the rear sprocket while doing a pivot donut. The derailed chain bunched up around the countershaft sprocket and cracked the top of my stator side cover. My theory is that while I had the bike leaned over for the donut, the chain did not have enough tension to stay engaged on the sprocket and gravity pulled the chain away from the sprocket allowing it to derail. I was able to get the chain back on, adjust the chain tension and keep riding...but I rode much more conservatively the rest of the day and that's no way to live your life IMO.

Admittedly and as evident by the attached pictures, chain maintenance is not my strong suit...I know I should do better, but I don't and since I have an engineering background, I decided to design around my inadequacies.

This is just a 3D printed prototype, but I should have the prototype aluminum plates and Delrin sliders (and proper hardware) in a couple weeks. The chain will be surrounded by delrin (or UHMW poly) in the guide. The guide will limit side play of the chain thereby preventing it from going far enough to derail so I think this is going to work. The current design should work with 47-50 tooth sprockets. 47T, 50T and 55T appear to be the most common on our bikes, so I will likely make a second design to work with 50-55 tooth sprockets depending on how well the early prototypes work and if there is any demand for it.

If the prototype testing goes well, I'll have some for sale around summer time.

213644


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Thats a very neat concept. If nothing else it should protect the chain well but damn dude, lube your chain haha. During the summer when i ride alot, ill lube mine once a week. Or you could get an o ring chain and not worry about lube i guess.
 

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My understanding is that the OEM white pplastic part isn't really a guide. Mine has 3/8"-1/2" clearance. It's purpose is to keep sticks and other trail debris from getting wedged between the chain and rear sprocket. If you tossed a chain it was because it was loose, your sprocket(s) are really worn, or your rear wheel was misaligned.
 

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Discussion Starter #4
Thats a very neat concept. If nothing else it should protect the chain well but damn dude, lube your chain haha. During the summer when i ride alot, ill lube mine once a week. Or you could get an o ring chain and not worry about lube i guess.
Haha...if I lube the chain I would be adding a second variable in addition to the new guide. By adding lube, I won't know if the lack of chain derailment is due to the lube or the guide. So for now I have to retain my crappy chain maintenance schedule...for science!
 

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‘04 TW200, Jets+Shims, DGV2, S-moto fender, Acerbis Guards, ProTaper KX, JNS DOT LED BLK, Moose Rack
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It's purpose is to keep sticks and other trail debris from getting wedged between the chain and rear sprocket.
Secondarily. Human fingers, hands & feet were the primary consideration of the design. Prior to that little advent in motorcycle design, riders/racers occasionally lost 1/2 a hand or 1/2 a foot, to the Asplundh that is the meeting point of the chain & rear sprocket - following a moving dismount.

OP - Nice engineering. Chain maintenance is like tire pressure, turn signal, or any other pre-flight checks and maintenance on the S.O.P. list. If you can't/don't make time for it, explore other hobbies.

I high-sided a sportbike as a young squid several decades ago, due to the exact same oversight. Chain fed off the rear sprocket in a left-hander, wrapped the axle & locked the rear wheel. Chain was stretched (one side tight, one side loose), overdue for swap, ordered the replacement literally one day before I wrecked the damn thing. Road impact cracked engine cover, oil drained out; other, mostly cosmetic damage. I was ATGATT back then, so thankfully, scraped & bruised only.

Never again, I told myself. Make the time.
 

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Discussion Starter #6
My understanding is that the OEM white pplastic part isn't really a guide. Mine has 3/8"-1/2" clearance. It's purpose is to keep sticks and other trail debris from getting wedged between the chain and rear sprocket. If you tossed a chain it was because it was loose, your sprocket(s) are really worn, or your rear wheel was misaligned.
Secondarily. Human fingers, hands & feet were the primary consideration of the design. Prior to that little advent in motorcycle design, riders/racers occasionally lost 1/2 a hand or 1/2 a foot, to Asplundh that is the meeting point of the chain & rear sprocket - following a moving dismount.

OP - Nice engineering. Chain maintenance is like tire pressure, turn signal, or any other pre-flight checks and maintenance on the S.O.P. list. If you can't/don't make time for it, explore other hobbies.

I high-sided a sportbike as a young squid several decades ago, due to the exact same oversight. Chain fed off the rear sprocket in a left-hander, wrapped the axle & locked the rear wheel. Chain was stretched (one side tight, one side loose), overdue for swap, ordered the replacement literally one day before I wrecked the damn thing. Road impact cracked engine case, oil drained out; other, mostly cosmetic damage. I was ATGATT back then, so thankfully, scraped & bruised only.

Never again, I told myself. Make the time.
Agreed...the stock part is a guard and not a guide. With proper chain maintenance and tension, a lot of people will likely never have a problem with chain derailment. However, most dual sport motorcycles have a chain guide to prevent/reduce the likelihood of derailment. I can only assume the TW does not for cost reasons. I also prefer to run a loose chain as chain tension increases with suspension compression and I've seen cracked cases and failed output shaft bearings on other bikes as a result of a chain tension set incorrectly (too tight). Again proper maintenance and this won't be a problem...but my goal is to make the bike less sensitive to my errors.
 

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Agreed...the stock part is a guard and not a guide. With proper chain maintenance and tension, a lot of people will likely never have a problem with chain derailment. However, most dual sport motorcycles have a chain guide to prevent/reduce the likelihood of derailment. I can only assume the TW does not for cost reasons. I also prefer to run a loose chain as chain tension increases with suspension compression and I've seen cracked cases and failed output shaft bearings on other bikes as a result of a chain tension set incorrectly (too tight). Again proper maintenance and this won't be a problem...but my goal is to make the bike less sensitive to my errors.
Gotcha. Sounds like you're well aware of the facts. Fun project. Keep us posted.
 

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Discussion Starter #9
It might be worth the effort to check your swingarm and rear tire bearings by jacking up and bike and seeing if stuff moves with lateral forces.
Good advice! The bike only has 1500 miles so I would be really surprised if any bearings were going bad at that low of mileage but you never know. I feel pretty confident that the chain tension was way too loose, but what you mentioned is easy to check as a precaution.
 

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Secondarily. Human fingers, hands & feet were the primary consideration of the design. Prior to that little advent in motorcycle design, riders/racers occasionally lost 1/2 a hand or 1/2 a foot, to Asplundh that is the meeting point of the chain & rear sprocket - following a moving dismount.
Where did you find that definition of Asplundh?
 

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I've experienced the "Asplundh".....several years ago on a meat slicer that I was repairing.
It was at that moment that I vowed to NEVER, EVER again, work on a rotating chain/sprocket. That instance only mulched the first phalanx of my index finger, because it was such a small sprocket, but to this day...I can still remember the sound it made, and the "WTF am I doing?" thought that ran through my mind as I watched my finger disappear into the machine.
 

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I've experienced the "Asplundh".....several years ago on a meat slicer that I was repairing.
It was at that moment that I vowed to NEVER, EVER again, work on a rotating chain/sprocket. That instance only mulched the first phalanx of my index finger, because it was such a small sprocket, but to this day...I can still remember the sound it made, and the "WTF am I doing?" thought that ran through my mind as I watched my finger disappear into the machine.
Plain horrifying, being de-digitized, I can only imagine (fortunately).
 

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I will suggest that if your pivot donut was executed on the left side, it may have been a freak scenario of the tire picking up a rock or stick, and gravity dropping it in just the right place between your sprocket & chain. ...It's conceivable this could occur with the bike leaning extremely to either side, with the tire digging in more than normal.
 

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Hi, did You consider put some chain tensioner instead? I am curently testing this solution. My t-dub has rised back and my chain has too much slack when unloaded. As for now this solution proves well and doesnt require any modification of swingarm itself.
bffdb825-758b-460a-99d1-7bd0b019a9a7.jpg 6c5fb5d3-0673-4e88-9b01-fb27214fbb85.jpg
 

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Hi, did You consider put some chain tensioner instead? I am curently testing this solution. My t-dub has rised back and my chain has too much slack when unloaded. As for now this solution proves well and doesnt require any modification of swingarm itself.
View attachment 213717 View attachment 213720
hello
i did, works great... but if you ride trails or over fallen branches on fire roads eventually one stick will flick up and completely rip it to sh!t and then your chain is really loose, and hope you have your tools along. Happened twice so i gave up and went with: from Aliexpress


no issues after 4000kms.
o
 

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hello
i did, works great... but if you ride trails or over fallen branches on fire roads eventually one stick will flick up and completely rip it to sh!t and then your chain is really loose, and hope you have your tools along. Happened twice so i gave up and went with: from Aliexpress


no issues after 4000kms.
o
Your link, it no work!
Found it anyways. You say this fits the TW200 o.k.?
 

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Discussion Starter #20
Hi, did You consider put some chain tensioner instead? I am curently testing this solution. My t-dub has rised back and my chain has too much slack when unloaded. As for now this solution proves well and doesnt require any modification of swingarm itself.
View attachment 213717 View attachment 213720
That's a pretty cool solution, but I tend to agree with OPZ...too many moving parts for off-road riding. But your experience may be different.
 
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