212cc Engine Reversal With Shift Kit

5-7HEAVEN

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Sprockets, chains and gearing.....

My clutch has a #41 10t sprocket.

To simplify things, I'll use all #41 gears.
They use 1/2' x 1/4" wide chain.

I choose #420 chain.
It is very strong & 1/4" wide.
#40 chain is just as strong but 5/16" wide.

Clutch 10t sprocket to 10t gearbox input.

Gearbox has 3.75:1 ratio.

Then 10t output sprocket to 27t chainring sprocket.

The ratio is 10.125:1 at the bottom bracket.

with 10.5:1 in First gear

and 5.25:1 in Seventh(final) gear.

Perfect.
 
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5-7HEAVEN

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Correction on the gear ratio calculations:

The driven chainring is 27t, but the drive chainring is 24t.

First gear is 11.81

High gear is 5.91.

Pretty low in Seventh gear, but ok.
 
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5-7HEAVEN

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I had some #40 chain laying around,so I’ll use it for this project.

It’s HUGE.
The 7-speed chain is 3/32” wide; this one is 5/16”(10/32”).

There seems to be enough space between the clutch sprocket and the engine side cover for the 40 chain,.
This is even with the 1/8” steel motor mount plate bolted on behind the clutch.
 

5-7HEAVEN

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I bit the bullet and ordered the Staton 18.75:1 gearbox, along with 10t sprockets and a 27t sprocket.

All sprockets are #41-type, which will work with the 10t clutch and #40 chain.

I’m not using the gearbox to mount an engine to it.
I’m using it as a transmission for my 212cc engine.

There are 3 shafts on the box. Two are input shafts, one is a mid drive shaft.


Using an output shaft and the mid drive sprocket will provide 3.75:1 gearing.

This allows me to get the proper gearing for my 7-speed bike.

As soon as the gearbox arrives, I’ll know what size steel mounting plate to order.

I also ordered a spare side cover to help with the mock up and drilling holes.
 
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5-7HEAVEN

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More measuring.

I ordered Staton gearbox, but there’s a delay, due to ice storm and major power outage in OK.

Given the dimensions by Bonefish, the box measures roughly 9” long x 3” thick x 5”.tall.

Looks like a 12” x 12” steel plate needs to be whittled down, to an upside down “L”fit.

I’ll do a cardboard mock-up.
 
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5-7HEAVEN

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It’s a challenging installation.:(

The long gearbox has to be mounted vertically low, outward and to the front right side.

The box’s thickness requires it to be positioned with all sprockets facing inward. Even the clutch.
If sprockets faced outward, they wouldn’t line up with the clutch and bottom bracket chain ring sprocket.

The low gear ratio, moving the exhaust far away from the riders legs and an easy shift kit installation are reasons to consider this setup.
 

5-7HEAVEN

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Still waiting for my Staton gearbox,:(

I miscalculated slightly, so the sprockets I ordered makes final drive at 5.91:1.

Installing a smaller gearbox sprocket raises it to 4.73:1 - 5.32:1.

In the meantime, still measuring.

The gearbox could be mounted at
any position except above the clutch,
and chain itself to the bottom bracket and clutch.
 
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