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I have an issue with the cranks. The chain would scrub in a gear I wanted, 20 tooth cog, so I reversed the spindle and got 6mm more room which worked. But there's only a few threads on the spindle to secure the crank arm with. I thought both ends of spindles were the same. It's on there but only half threaded on. I checked my other spindles and they all look the same as this one.
23 Dec drivetrain.jpg


The tensioner is used for the 18 tooth cog, 20 doesn't need tension. Shift by hand. With the weight of this thing, it will probably stay in the 39/20 setup.
 
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For a 4 inch wide tire, you have to use a wide hub. I tried using a standard width hub and dish it over, but it still couldn't get the low gears. I found a good hub and laced up the wheel again. Next I'll see if the standard width cranks will work, allowing the lowest gear without rubbing. I went with a 190mm hub to get the most width. I'm also going to use disc brakes for the first time.

190mm hub.jpg
 
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I laid out some things to get a better idea of what I was doing. I think I'll have twin bars go all the way back and be part of the dropouts, like seat stays. The floor tiles of my shop gives me a straightedge to determine the clearance of my pedals and the angle of my head tube and seat tube. The rear wheel is sitting right about where it will attach.
17 Mar layout.jpg


The springer could look better as the spring cage looks too small for the 5" wide gap. I have plenty of steel I can use to make a cage that spans the opening there better, and will have room for two springs. I also dug out some dropouts to use. I'm hoping to have the rear part of the frame look good, not like a high school welding project.
17 Mar 23 spring.jpg


17 Mar 23 springs.jpg
 
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I've got disc brakes and adapters ordered, also for the front with an adapter.
I laid out the drops with vice grips after bending the chain stays for the wide rim. I bent them halfway back to make room for the cranks, it's a standard width BB.
19 Mar 23 190mm spacing.jpg


19 Mar 23 layout.jpg


It lines up nicely with the stays and the twin bars that will transverse the bike. I had thought of bending the twin bars to fit the 4" tire, but it will clear the tire without bending. That should be better for strength as they will be the seat stays. I just have to brace it at the seat post where there will be a 3"+ gap. Maybe a plate welded in. The twin bars also look like the ends will slide in the existing tubing on the drops, so welding them up should look pretty clean. I may just bolt up the bottom halves instead of welding to get a little adjustment if need be.
19 Mar 23 bars.jpg


Finally for today I checked the fitting of the wheel and it looked good. I finished up at 1100 am, it's too hot already. And I couldn't do any cutting or grinding with clothes hanging up drying in the shop.

19 Mar 23 clearance.jpg
 
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I still can't do any cutting or grinding, so I laid out some stuff for the springer mod. I had a part wide enough that will work.. It just needs a couple cuts and a few holes drilled. Then a plate for the springs in the front and it should be ready to go. I noticed I need a 1/2" longer bolt for the pivot point when I checked the alignment of the forks.

20 Mar 23 springer.jpg
 
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Clothes are still hanging in the shop, but I know better than to complain. I was able to measure some things and drill some holes to get a look at the plan. It is working out so far. I need to cut the excess off and make sure I have good hardware throughout.

20 Mar 23 springer2.jpg

You can see where the pivot bolt needs to be a half inch longer. There's no room for a washer on the acorn nut.
20 Mar 23 springer3.jpg


20 Mar 23 springer1.jpg
 
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The dropouts fit right into the tubing like I had hoped. They will get welded later when everything else lines up.
23 Mar 23 drops.jpg



I made the cuts to the springer cage and it is almost ready. I'm getting different bolts for the springs, those old ones are threaded all the way and the ends need to be smooth to slide back and forth through the cage. I mocked up the frame and will try to get the wheels on tomorrow.

23 Mar 23 frame fork.jpg
 

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