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BLACK BELT
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6,913 Posts
Discussion Starter #121
I have to give up for a while. I'm (obviously) no expert at this, and the tolerances are too close to measure accurately with my setup.

The bigger issue that has come up is the chain hitting the bottom of the swingarm when the rear suspension compresses a lot. It may not be an issue if I lower the engine to align the front sprocket and pivot, but I'd also like to go from a 16-tooth to a 15-tooth front sprocket, which will make matters worse.

For now, I'll probably get the wheels, tires and rear sprocket, and also a correct sized rod for a swingarm pivot - then I should be able to get more accurate measurements.
 

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GURU
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8,827 Posts
i run a roller on the bottom end of my bike because of my swingarm angle there is frame clerance issues. Mine is mounted off one of the old center stand mounting points and i run an MX chain roller. The issue with running a sprocket as an idler is you will need to ensure it always has contact. With my roller the issue is only there on hard decel when the rear is unloaded and the bottom of the chain has tension on it.

here is an old pic of it with no chain.



i dont have any good pics of it when the chain is on but you can see it here.



I think really in your case it might be to your benefit to mod the swingarm and run a sprocket around your swingarm pivot(two sprockets, drive and driven). this would let you push the motor up/forward and also get rid of any chain tension issues since it will be centered on the pivot.
 

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BLACK BELT
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6,913 Posts
Discussion Starter #124
I think really in your case it might be to your benefit to mod the swingarm and run a sprocket around your swingarm pivot(two sprockets, drive and driven). this would let you push the motor up/forward and also get rid of any chain tension issues since it will be centered on the pivot.
I saw a similar idea on a page from Tony Foale's chassis book, but thought it was ridiculous to chop the whole left pivot off. Now that I realize the chain will still rub on the bottom of the pivot with the idler sprocket , the twin sprocket idea is looking better (although if i use the idler and teflon guard on the bottom, I don't have to chop the swingarm).

Thanks for recognizing the issue and posting the idea, it always seems less wacky when someone else suggests it. :knucks:



The blue part on the left would need to be chopped out for the sprockets, and the blue part on the right would need to be added for support. A solid plate could also be welded in to support the cut area.



Driven chain on the left, drive chain on the right.



There may not be enough clearance for the sprockets and chain - I can't get good measurements without the rear sprocket in place and better alignment of the engine/frame/swingarm.
 

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Commander Cool
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9,707 Posts
looks painfully technical. i fuckin love it, and hope you can pull it off. lets see how it goes, seeing as you've already produced a bitchin ass streetfighter...
 

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jamal avatar #1
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3,443 Posts
I want to tuck the engine up into the frame to get the maximum ground clearance. With the downpipes, the clearance is already too little for a supermoto bike - and I don't want the pipes to scrape the ground.

The SXV needs a lot of ground clearance because the suspension compresses a lot. I've seen pics and video of guys dragging the footpegs through the corners (with their feet on them), and they even sell footpeg sliders for this bike.







your not riding a sumo properly unless your pegs are making contact :shocker:

very impressive so far, alot better then going out and getting a xmoto or drz.
 
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GURU
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8,827 Posts
I saw a similar idea on a page from Tony Foale's chassis book, but thought it was ridiculous to chop the whole left pivot off. Now that I realize the chain will still rub on the bottom of the pivot with the idler sprocket , the twin sprocket idea is looking better (although if i use the idler and teflon guard on the bottom, I don't have to chop the swingarm).

Thanks for recognizing the issue and posting the idea, it always seems less wacky when someone else suggests it. :knucks:



The blue part on the left would need to be chopped out for the sprockets, and the blue part on the right would need to be added for support. A solid plate could also be welded in to support the cut area.



Driven chain on the left, drive chain on the right.



There may not be enough clearance for the sprockets and chain - I can't get good measurements without the rear sprocket in place and better alignment of the engine/frame/swingarm.

If you dont need the area where the stock 5.5 motor went between the swingarm i would brace that whole area across. Im sure there are tons of pictures on the internet about this kind of think. Most people do it when they want to run un godly wide tires on the rear. Even though its a lot of swingarm fab it will be less frame fab i think and monetarily speaking that may be the best option ;) Do you have another swingarm you can play with for mock ups(not aprilia)?
 

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Ridin' Dirty
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6,773 Posts
IMHO, the chain hitting the swinger isn't as big an issue as you're thinking. Think about dirt bikes. On some of them the chains are slapping the swinger constantly. My brother has a late 90s kx80 and the swinger is soo long and the countershaft sprocket is soo small, that the chain is almost always either hitting the top or the bottom of the swinger. There is a thick plastic guard that wraps around the swinger and when it wears out, you just replace it. I'm sure you already know all this, just making sure in case.

Use something like part 12053B

 

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GURU
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8,827 Posts
IMHO, the chain hitting the swinger isn't as big an issue as you're thinking. Think about dirt bikes. On some of them the chains are slapping the swinger constantly. My brother has a late 90s kx80 and the swinger is soo long and the countershaft sprocket is soo small, that the chain is almost always either hitting the top or the bottom of the swinger. There is a thick plastic guard that wraps around the swinger and when it wears out, you just replace it. I'm sure you already know all this, just making sure in case.

Use something like part 12053B

dirt bike have to do that because of the amount of travel. this is also why they have a chain guide and rollers above and below the swinger. Dirtbikes also dont "cruise" so the chain doesnt always ride on the guide. All bikes(chain driven) have that guide on the swing arm pivot and while some times the chain rides on this, under most conditions when the top is under tension it doesnt.
 

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Hooligan Streetfighter
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1,382 Posts
Good read and interesting build. I know that there is someone out there tha tmakes the jockey sprocket you are looking for. I will try to find the info. I know they make them to your specs, all you have to do is tell the distance between the sprockets. I will try to find it and get back to you.
 

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Ridin' Dirty
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6,773 Posts
It was just a thought, I wasn't sure if Smoker's build issue was the chain constantly riding on the swinger or just under full extension or compression. Running as big a countershaft sprocket as possible might help.

I've owned my fair share of dirtbikes and on most of them the little slider piece and the upper and lower rollers are only hitting the chain under full compression or extension, like you said. I just brought up the kx80 because it seemed like an extreme example.

I see you point about the long travel of dirtbikes, but it is a supermoto bike, Smoker, you gonna run OE suspension or are you lowering it and stiffening it up?
 

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BLACK BELT
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6,913 Posts
Discussion Starter #136
The new BMW motocrosser swingarm pivot:



Perhaps the single most impressive design element of the G450X is the exclusive implementation of a coaxial swingarm pivot/countershaft. A hollow countershaft serves as the swingarm pivot bolt hole, allowing the countershaft sprocket to rotate around the swingarm pivot point. This completely eliminates the need to adjust the chain to accommodate the wild variations in tension due to 12 inches of rear wheel travel. It’s a surprisingly simple solution to a problem that has been the bane of long-travel suspension since its introduction over 35 years ago. It’s ironic that BMW would be the first manufacturer (not counting start-up MotoCzysz) to implement this ingenious design.

An added bonus of the coaxial design, which translates into chain tension remaining constant regardless of rear wheel travel, is that the stresses on the countershaft and transmission are greatly reduced. Removing this variance will undoubtedly prolong chain and sprocket life in addition to removing concerns over proper chain adjustment to accommodate the full arc of travel.
 

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NZ = NOT AUSTRALIA.
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611 Posts
All these toys im in the wrong profession, seriously...

A) what do you for a job...

B) hiring?

Envy is a bitch lol
 

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fighter transplant in NC
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14,319 Posts
He's a nurse, and if you have the creds, hosppitals are always hiring
 

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GURU
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8,827 Posts
The new BMW motocrosser swingarm pivot:



Perhaps the single most impressive design element of the G450X is the exclusive implementation of a coaxial swingarm pivot/countershaft. A hollow countershaft serves as the swingarm pivot bolt hole, allowing the countershaft sprocket to rotate around the swingarm pivot point. This completely eliminates the need to adjust the chain to accommodate the wild variations in tension due to 12 inches of rear wheel travel. It’s a surprisingly simple solution to a problem that has been the bane of long-travel suspension since its introduction over 35 years ago. It’s ironic that BMW would be the first manufacturer (not counting start-up MotoCzysz) to implement this ingenious design.

An added bonus of the coaxial design, which translates into chain tension remaining constant regardless of rear wheel travel, is that the stresses on the countershaft and transmission are greatly reduced. Removing this variance will undoubtedly prolong chain and sprocket life in addition to removing concerns over proper chain adjustment to accommodate the full arc of travel.

its a thing of beauty. In the bike/motor ive been working on i had that in the design ;).
 
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