Chain Tensioner Need Help With GT Lts Full Suspension Chain Issues

Gotdam47

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Apr 1, 2018
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8
Hi all,

I have just finished constructing a full suspension motorized bike on a gt lts frame. I have been using one spring tensioner attached to the frame and one stock tensioner pushing up on the chain. The chain loses tension quite rapidly whenever weight is put on the bike. I cannot start the bike as whenever you release the clutch at speed, the chain bunches up in the clutch case, and the back wheel locks up. This is a direct drive to a 44t sprocket. I have tried moving the tensioners every which way, but nothing seems to remedy the problem. I am quite desperate for help at this point, so any ideas or advice is greatly appreciated.
 


FurryOnTheInside

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Sep 23, 2013
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3,630
Hi all,

I have just finished constructing a full suspension motorized bike on a gt lts frame. I have been using one spring tensioner attached to the frame and one stock tensioner pushing up on the chain. The chain loses tension quite rapidly whenever weight is put on the bike. I cannot start the bike as whenever you release the clutch at speed, the chain bunches up in the clutch case, and the back wheel locks up. This is a direct drive to a 44t sprocket. I have tried moving the tensioners every which way, but nothing seems to remedy the problem. I am quite desperate for help at this point, so any ideas or advice is greatly appreciated.
Hi I have a GT LTS 5 (the bottom of the range 4130 chromoly one) but I have not tried to motorise it yet. I have had a good look at the frame though, and I have some ideas from my first build on a rigid frame. I hope some of these will help you with your build. :)

You mentioned that the chain bunches up under the sprocket cover. This would be caused by the slack in the top run of chain, but it is allowed by the excess and badly shaped space inside the sprocket case.
This can be filled up very easily.


View media item 61320I used cereal box around the chain to make a mould, then cheap 2 part epoxy resin poured into the space while the bike was on its side. I tore the cereal box out and gave it a quick scrape with a knife. I probably could have greased the cereal box but I was worried that I would touch the case and prevent proper adhesion, and I did so it would have lol.
That stops the chain from bunching up. You might still want to have the slack better controlled though, and there will (has to be) always be some slack in the upper run of chain when you shut off the throttle. Some type of chain slider certainly helps.
I used the RSP chain controller (meant to go under the chainstay on MTBs before better technology came along), which fits up to #410 (1/8" bmx) chains, to stop the bouncing/whip of the upper run of chain when I open and shut off the throttle at high speed, ride over rough terrain, or just ride fast. I'm sure something along those lines could help your build too. It could be something home made, possibly larger or more cone shaped and I think probably wants to be attached to the engine due to your suspension.



If the fixed pulley tensioner for the lower run of chain is attached to the seat stay, I believe that will work much better than if it's attached to the chain stay, due to the location of the rear pivots in the LTS' Horst link frame design. This would mean that you'll have to make the tensioner mount/ arm that the pulley hangs from as it will be longer than the kit tensioner mount/ arm that usually stands up from the chain stay.
The stock pulley could really use an upgrade, anyway. It isn't great plastic or good bearings. There are similar but more heavy duty ones made for pit bikes etc, or higher quality ones made for MTB chain retainers. The mtb ones have better sealed bearings but can often be a bit narrow for #410 chain, but I found some that are made to fit to MTBs with two chainrings. That's what I used (and repurposed the mount/ arm too) on my rigid frame.

I believe one of the things that will really make the chain easier to control would be to make it weigh less. If you are using the kit #415 chain then IMHO that the excess mass is part of the problem. If you want to try a lighter #410 then you'll probably have to make the front (and maybe rear?) sprocket narrower as the #415 has 3/16" wide rollers and the #410 bmx chain has 1/8" rollers. It needs a sprocket with teeth 0.120" thick to fit it really well. I have just switched to 9 speed chain but I think that could do more harm than good on a single speed build because it can bend side to side.
The technique I use to narrow the front sprocket is to secure it on a bamboo cane with a sliver of softwood hammered in so I can easily turn it while holding it to the bench grinder, then drop the cane through a hole in my workbench for the later stage of finishing the new shape of the teeth with a rotary tool and diamond file.
View media item 61322
View media item 61321If you do narrow the sprocket in this way it gives you the opportunity to fine tune the alignment by choosing the right side of the sprocket to grind back. :)
 
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Gotdam47

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Apr 1, 2018
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Thank you so much for the advice. I think I can make this work. I have a machine shop near my house that could probably make some custom chain sliders and tensioners. I will also follow the clutch case rounding method you showed me. Will update on how it goes if you would like. Thanks again.
 

FurryOnTheInside

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Sep 23, 2013
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Thank you so much for the advice. I think I can make this work. I have a machine shop near my house that could probably make some custom chain sliders and tensioners. I will also follow the clutch case rounding method you showed me. Will update on how it goes if you would like. Thanks again.
No problem, happy I could help, and I will be looking forward to seeing how your "chain management system" turns out. :)
 

gary55

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Joined
Nov 27, 2012
Messages
3,825
Hi all,

I have just finished constructing a full suspension motorized bike on a gt lts frame. I have been using one spring tensioner attached to the frame and one stock tensioner pushing up on the chain. The chain loses tension quite rapidly whenever weight is put on the bike. I cannot start the bike as whenever you release the clutch at speed, the chain bunches up in the clutch case, and the back wheel locks up. This is a direct drive to a 44t sprocket. I have tried moving the tensioners every which way, but nothing seems to remedy the problem. I am quite desperate for help at this point, so any ideas or advice is greatly appreciated.
You would need a strong spring operated tensioner to overcome the slack created by all the travel in the swing arm. If I had that frame I would be looking to see if I could get a sickbikeparts shifter kit to fit on it. This would eliminate the problem and make the bike a much better performing machine. I don't know what kinda budget your working with, but the bike your working with would make a really cool shifter bike. I would also shell out the doe for a Nuvinci hub. It would be pricey, but well worth it. It would take off from a dead stop, climb hills like a goat, cruise at 30 with no strain on the engine, and do it all smoothly.
View media item 60711
View media item 60710
 

FurryOnTheInside

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Sep 23, 2013
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3,630
You would need a strong spring operated tensioner to overcome the slack created by all the travel in the swing arm. If I had that frame I would be looking to see if I could get a sickbikeparts shifter kit to fit on it. This would eliminate the problem and make the bike a much better performing machine. I don't know what kinda budget your working with, but the bike your working with would make a really cool shifter bike. I would also shell out the doe for a Nuvinci hub. It would be pricey, but well worth it. It would take off from a dead stop, climb hills like a goat, cruise at 30 with no strain on the engine, and do it all smoothly.
View media item 60711
View media item 60710
I totally agree that the Sick Bike Parts Shift Kit would be the best way to use the GT LTS frame, if the budget allows.
 

gary55

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Nov 27, 2012
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I totally agree that the Sick Bike Parts Shift Kit would be the best way to use the GT LTS frame, if the budget allows.
I read where you said you have a LTS frame. If you put the attention for detail into a shifter LTS that you put into Furry it would be amazing.
 

FurryOnTheInside

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Sep 23, 2013
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I read where you said you have a LTS frame. If you put the attention for detail into a shifter LTS that you put into Furry it would be amazing.
Thanks for the compliment. :")
The thing is, the Shift Kit is expensive, especially to import to the UK. My LTS 5 is the bottom of the range short travel one so I would probably just do a more economical single speed build on it.
I already have a hardtail mountain bike style build I want to put a special Shift Kit on, I have a lot of the parts already. :)
 

gary55

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Nov 27, 2012
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3,825
Thanks for the compliment. :")
The thing is, the Shift Kit is expensive, especially to import to the UK. My LTS 5 is the bottom of the range short travel one so I would probably just do a more economical single speed build on it.
I already have a hardtail mountain bike style build I want to put a special Shift Kit on, I have a lot of the parts already. :)
Just calls em like I sees em.
 

Gotdam47

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Apr 1, 2018
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As for budget, I am pretty much at the end of my ropes for now. I found a hard tail frame in my garage so I may move the bike parts over to it and rebuild the engine on it. We shall see. Shift Kit would be nice though, not gonna lie.
 
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