Dual Chain Transmission Won't Fit

This may be helpful. According to the video the 5G reduction is around 6.83:1. Using the 10:44 gives you a total reduction around 30:1. Depending on your son's weight, the weight of the build, the engine size and the hill grade you may need as much as a 55:1 reduction to get up the hill. I live in Tennessee where there's a 50cc limit and an automatic transmission clause. Small engines, large people and steep hills means you must have gears. My way of getting around the automatic transmission clause was to build a bike that shifts engine gears automatically.

 
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Wow, that's a lot of advice! Thanks so much. Our build is on a beach cruiser with a coaster brake. This was intentional, because we wanted it as simple as possible for my son's safety. Gas to go and brake to stop, nothing else.
I've thought about putting washers on the four bolts to pull it out a bit, but then there would be a small gap between the gear box and the engine. Also, I'm concerned that the entire depth of the clutch hammers (not sure what you call the three arms that come out) would not strike the bell, thus reducing the frictional grab.
I thought about taking the bell off and possibly putting on a smaller center nut and bolt, however if that doesn't work then I can't return it.
Final thought, should I just return it and get a belt drive? My son is chomping at the bit to go, go, go.
Safety means having a good braking system for going down steep hills. Coaster brakes lock the tire and can send him into a skid. All I use is rim brakes but very high quality pads. A set cost around $50. Parts of NC are like Tennessee as far as steep hills go.

There's a road in Gatlinburg which is over a 30% grade and about a mile long. The peak of the hill is about mid way of the road. Stop signs are at each end of the road. What this means is you have to bump brake on the decent; otherwise you'll be doing over 50 mph as you're approaching a stop sign.
 
Phil, I too purchased the BB duel chain and had the exact same problem with it not fitting...

I DID get it to fit with a little work though!

So, I first removed the nut and bell from the BB trans and the original nut and bell from the stock single chain set. The BB bell was not as deep as my original so I wanted to replace it and the nut since it was thinner than BB's nut.

I dismantled the BB trans, than used a cutting wheel to remove roughly 1/8 of an inch off the threaded shaft... I had to estimate since I didn't have a cutting guide for this as I was at my job when I did it...

I reassembled the BB trans using my old bell and nut and mounted it like I would normally have done. The case mounted flush to engine so I got my back wheel up and gave the cord a few slow pulls to make sure the bell wasn't putting pressure on the flywheel. Thankfully it wasn't, so I fired the engine up, took the choke off and revved up. Worked like a dream!

Hope this helps!
 
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dont know if this is solved yet but there is a skinny head bolt that needs to be changed to use the dual chain gearbox so just grind the bolt you have or go to a local hardware store with the bolt that holds clutch and ask for a thinner head
 
Phil, I too purchased the BB duel chain and had the exact same problem with it not fitting...

I DID get it to fit with a little work though!

So, I first removed the nut and bell from the BB trans and the original nut and bell from the stock single chain set. The BB bell was not as deep as my original so I wanted to replace it and the nut since it was thinner than BB's nut.

I dismantled the BB trans, than used a cutting wheel to remove roughly 1/8 of an inch off the threaded shaft... I had to estimate since I didn't have a cutting guide for this as I was at my job when I did it...

I reassembled the BB trans using my old bell and nut and mounted it like I would normally have done. The case mounted flush to engine so I got my back wheel up and gave the cord a few slow pulls to make sure the bell wasn't putting pressure on the flywheel. Thankfully it wasn't, so I fired the engine up, took the choke off and revved up. Worked like a dream!

Hope this helps!
check to see if you need to grind more or add a spacer by looking at the pads after riding a while to see if the wear and tear is lined up
 
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