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Here is my idea for dual sprockets. Please feel free to inform me what won't work!

I would like to run dual front sprockets only. 13 and 15 tooth with my stock 50 tooth rear. I would also like to be able to change from one to the other only loosening the rear axle, not taking the chain apart. My thinking is that if its too much work, I just won't change sprockets very often and won't be taking advantage of the setup.

Is there enough room in the side cover for the chain to go over the top of the 15t sprocket and slide over to the 13t?

If you are going to spend the time to do a dual front, you might as well do the rear also for even more flexibility. I did both front and rear and with this, chain alignment is perfect for each 'set'. The 13 will be tough to index as the diameter is to small for screw hole for securing the mated pair. The primary shaft splines are only long enough for one sprocket, the sister sprocket will need the splines removed so it can slide over the shaft. My first set I did in my shop on a drill press with grinding stones (cone). I suggest you make the splined position on the shaft available for your off-road/trail gear combination. I was able to do six teeth without having to worry about adding chain sections to accommodate my sprocket combinations (15-50 & 14-55). Good luck. I am as well working on another front combo.
 

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You do some really nice machining out of your shop Gerry. Really like the center spacer. Assembly looks to have greater shear strength than your proof of concept prototype I saw at the Cow Mtn #2 Group Ride. I wonder if whole assembly could be braised together for even greater strength without compromising balance of tooth hardness vs. toughness.
 

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Well it took awhile. Got some great ideas from forum members following the failure of my dual front sprocket set-up. While on my first Nor-Cal ride mrgizmow managed to make it two blocks. Seems I had (but did not realize) a drive train disconnect. Nothing catastrophic, as the un-splined sister sprocket simply separated from the stock sprocket to which it was mated. I had been riding this combination for the last 2000 miles or so. After some time, lots of thinking and a couple additions to my shop, I was able to incorporate a couple of your suggestions. Not going to spend much time explaining as my hope is, a picture is worth a thousand words. The project has been handed off to someone that is very familiar with unique mods. If the project has merit, likely findings and opinions will be presented. I put the updated version on my bike and feel ok, but my needs are modest. Remember, this picture will have to do for now. (13/15).
 

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This is a really interesting thread. Took me a couple days to read it all. Last Spring when I was looking for a used/old/vintage dirt bike (always magnetically drawn to some hopeless project of some sort) I saw several listings on eBay from a company called Kaplan Cycles in CT, maybe some of you might have seen their auctions? They were selling a lot of their collection to help fund some sort of CT. Motorcycle Museum. Always had/has interesting stuff for sale and do a great video presentation. At some point they were selling a lot of bikes from someone named "FlatHead Jack", well known racer from the 60'-70's. They acquired 80 plus bikes from his collection, assuming Flathead must have passed on? Several of the bikes, particularly a couple Suzuki's had dual-sproket set-ups. At least in the rear. Not sure about the front. I don't know if they changed gearing during or between races but it always looked like a great idea.

Here's a collection of their video's on youtube. If you "load more images" you'll eventually find the Zuki's with the dual-sproket set-up I'm referring to:
https://www.youtube.com/channel/UCH83p-r3mtrw-cE58WQo0Fg/videos
 

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Brian,
Looking closely at the picture you shared, it looks like you have a triple rear sprocket setup.
Is that correct, or are my aging eyes confusing me?:glasses9:
 

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I have one of Gerry's 12/15 dual front sprocket combos poised for an install, just can't decide to restore it onto MrGizmo bike with the dual rear sprockets, or replace Betty Boop's 13 tooth to drive my 55 toothed Duro. Either way I'ld likely end up with a unique Transformer W​agon.
 
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Fred,
Have you experienced any issues with running a 13 and especially a 12 tooth front sprocket for chain wear and excessive front sprocket wear?
 

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Good to see you putting 'mrgizmow' to work. Bet the machine had no idea it could go so fast. You seemed a bit perplex as to how best go about repositioning the chain on the front sprockets. Since I was/am mostly an off pavement guy, after a couple of change overs, I found my trail combination worked best for me so there was little changing from that point on. When needing to switch, I loosened the axle nut while the bike was on the side stand. I would then raise the right back side of my swingarm with my 'crutch' jack. With this, I was able to rotate the wheel so that it pushed the top of the chain forward. With a finger, I would push or pull the side of the chain close to the front. Seemed for me, the chain would rise up or drop to the adjacent sprocket without much fuss.



The picture below shows a section of the case that was trimmed. The cutout was more for me to easily double check the condition of my setup. This should not be needed if you have adequate chain slack and 'push' the chain by rotating the raised rear wheel. As I always carry tools and my 'crutch' jack. A sprocket/chain switch over could be done in less than ten minutes trailside. That should include getting out and putting away your axle wrench and jack.

..
 

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​Hope you enjoy the versatility that the 13/15 combo should offer you. Unlike Brian's combo, yours has the 13 in the stock splined position and the 15 (road) is the 'sister' pinned sprocket. Should the unlikely happen as did it for me on the Cow mountain ride, you will always have the stock positioned (factory splined) sprocket to rely on.
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IN ADDITION, SINCE YOU LIKE TO TAKE THE BULL BY THE HORNS SORT TA SPEAK,
PLEASE USE CAUTION. WORK THE 'BACKYARD PROTOTYPE' SPROCKET SETUP INTO A POSITION OF TRUST SLOWLY. I AM VERY HAPPY WITH THE WAY IT TURNED OUT, BUT I AM NO ENGINEER. A FAILURE AT SPEED COULD BE A VERY UNPLEASANT EXPERIENCE.
Take care.
 

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Thanks Gerry. I still have the dual sprocket in an unopened parts bag uninstallled, it is labeled 12/15.
I have been content with running the "safe" single sprocket while dealing with other life issues. Should change out as on my last Gizmo outing my initial road gearing left me a little long legged when I took some unplanned technical steep stuff.
My magic MrGizmo magnetic rear axle snail adjuster had gone missing, undoubtedly stuck to backside of a tool box or under the seat frame of one of my vehicles...so chain adjustments on the trail are not as easy.
I should replicate Gerry's ingenuity...basically a foot long rod with 2 round "nubs" that protrude radially engaging the corresponding round holes in the swing arm"s snail cams. The magnet of Generation 2 simply keeps the tool engaged with the snails.
We could maybe get MBW to say that everyone should make their own MrGizmo chain adjusting tool. It really makes axle positioning/ chain length adjustments so very much easier.
 
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Glad the adjusting tool has worked out so well. Have not had much feedback regarding the valve adjuster. The snail wrench I carry is made from a 3/16" strip about 1/2" wide with a section of vinyl tubing over the handle . The welding was a bit simpler and the tool just a tad lighter. Just bought a new welder and being a retired guy I do have some extra time on my hands should someone want an original mrgizmow snail wrench. Suspect my marking on your parts bag is incorrect. The retention pin position was getting very close to the nesting area of the side plates of the chain I suspect the smaller diameter of a twelve tooth sprocket would conflict with the dimensions I used.
 

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TW Brian
i would like to do the same set-up.
how many link are you running on your 55T/65T set up?
and how many spacers or washers and where?
thanks
Hi rvflorian,

I have done so many different combinations of front/rear sprockets, that I can't keep track of the exact configuration of all of them. I am also running a 2" extended swingarm (thanks again Joemama!), so my length of chain would not apply to a stock swingarm. Sorry:(.

Here are my suggestions for your dual rear sprocket setup. Order the sprockets with a center recess cut into them. This will help provide some extra clearance that you will need because there is not a lot of space back there. Regarding the spacers, just buy a bunch of washers and nuts from the hardware store and plan on playing around with different stackups until you find the one that works best at allowing clearance for the chain between the spockets, and between the sprockets/nuts and the swingarm. It's not rocket surgery, just a lot of bolting up and upbolting things.

Here is a link to the last couple of chains that I have bought for these multiple sprockets combos. It is 132 links and I suggest that you order a couple of extra master links at the same time. Cut the chain to fit your smaller rear sprocket, then figure how long of a piece of chain that you will need to add to fit your larger sprocket.

I hope this is helpful,

Brian

KMC O-Ring Chain 428UO x 132L
 

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....
Cut the chain to fit your smaller rear sprocket, then figure how long of a piece of chain that you will need to add to fit your larger sprocket.

I hope this is helpful,

Brian

KMC O-Ring Chain 428UO x 132L
Forgive me if I'm missing something, but why not cut the chain to fit the larger sprocket first. Then put that length of chain around the smaller sprocket. Cut off the overlap and that is the number of links you'll need to add to fit the large one again ?
 

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Or use that big muscle between the ears and figure required chain lengths out in advance.
Take stock chain length and add 2 links for every inch of extended swing arm length, then add one link for every four additional rear sprocket teeth added beyond stock. The math is easy since our 428 drive chains links ( inner plus outer halves) are 1.0 inches long.
 
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Easy Dual Rear Sprocket Setup 45T/50T

These instructions require no cutting, no grinding, no fabricating, and should take less than ½ hour. This whole project costs less than $75 and uses all new stuff. Because I had swapped the original 50T rear sprocket for a 42T (and needed to shorten my chain), this post includes directions and materials to start from scratch.

After looking at this thread for a while I finally decided to give it a go. I took bits and pieces from everyone’s advice and complied what I thought would be the easiest and ideal setup.

As a few suggested, I went with the recessed JT Sprockets. I believe this is what made everything go so easily. This setup uses the 45T sprocket on the inside and the 50T on the outside. The 45T will be mounted against the wheel hub with the RECESSED SIDE FACING IN (facing the hub and wheel spokes). This will very slightly offset this sprocket from its original alignment and creates a similar slight misalignment for the other sprocket. The outside 50T sprocket will be mounted with the RECESSED SIDE FACING OUT.

HARDWARE:
JT Sprockets JTC428HDR122SL 428 HDR 122-Link Heavy Duty Drive Chain ($21.29)
JT Sprockets JTR1842.45 45T Steel Rear Sprocket ($23.17)
JT Sprockets JTR1842.50 50T Steel Rear Sprocket ($21.09)
(6) Bolts (8.8 Grade) M8 x 1.25 x 40mm
(18) Washers, M8
(6) Nuts, M8 x 1.25 (regular sized nuts)
(6) Jam Nuts, M8 x 1.25 (half the thickness of common nuts)
(6) Lock Nuts/Stop Nuts M8 x 1.25 (blue or white nylon inside)

NOTE: This is the order things need to go on, from outside to inside:
Bolt, Washer, 50T Sprocket, Nut, 45T Sprocket, Wheel Hub, Washer, Jam Nut, Locknut

Remove the chain guard and the sprocket protector thing. Remove the wheel entirely and remove original sprocket. You will not need any of the original bolts or other pieces. Lay the wheel flat with the hub facing up.

1.) First thread all 6 bolts (with a washer on each) through the 50T sprocket. The bolt head and washers should be sitting inside the recessed part of the sprocket. Remember, this 50T will be the outside sprocket and the RECESSED SIDE will be facing OUT.

2.) Using the regular size nuts and 6 washers, spin them on to each of the bolts. DO NOT tighten yet. (There needs to be some play to get through the hub.)

3.) Mount the 45T sprocket on the wheel hub, RECESSED SIDE DOWN, facing the hub. It should be a nice snug fit. Make sure the wholes are lined up.

4.) Mount the 50T sprocket onto the 45T sprocket (and through the hub). Since the bolts were left loose it should slip right in.

5.) Add a washer and jam nut (the thinner nuts) to each bolt, and hand-tighten.

6.) Now you will need to tighten the nuts in between the two sprockets. There should be plenty of room for a wrench because we are using regular sized nuts in between.

7.) Now you can tighten the Jams Nuts on the inside of the hub (the ones we hand-tightened earlier).

8.) Finally, add a Lock Nut to each of the bolts and tighten.

9.) NOTE: The white nylon, sprocket protector thing, can be remounted BUT you will need to add about two or three thin washers on each bolt or these little bolts will interfere with the 50T sprocket. You WILL need to bend the metal mount the sprocket protector thing screws into out of the way a little bit or the bolt heads will rub. The chain guard cannot be remounted unless you do some modifications.

This specific setup allows for plenty of slack to easily slip the chain from one gear to the other. You’ll notice that at this chain length, the 45T sprocket is pretty much as high of a gear you could put on the inside. The chain is maxed out and the axle is all the way back. However, there seems to be enough slack up front if you wanted to experiment with even lower gearing than the 50T used here.

I hope this helps.
 

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