Conversion of Chinese Belt Drive to 4:1 with Grubee 80T Pulley

Mike St

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I have purchased a Grubee solid 80T pulley to convert the Chinese belt drive
drive from 5:1 (100T pulley) to 4:1 (80T pulley). This idea was suggested by
Nirve. This will raise the theoretical top speed from 26mph to 32 mph.
Instead of sanding down the shaft that the pulley goes on, I will remove
material from the pulley hole by hand, so the change is reversible. Can't
use a hone because of the keyway groove. Bicycle-Engines.com is
dropping 4 stroke kits and has the Grubee parts on a clearance sale.
Here's the part:
https://www.bicycle-engines.com/4g-...rocket-for-grubee-4-stroke-t-belt-drive-kits/
Also purchased a smaller belt for the 80T.
 

Mike St

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I think the 4:1 gives me more options. I'm aiming for a sweet spot,
using 41 T rear sprocket and prefer not to change out the rear
wheel sprocket. And I want to learn how to do this so I can
use a 100T or an 80T. Actually, I want to prove a Grubee pulley
can be installed on an ebay Chinese belt drive. Once I get the 80T to
fit, I'll be able to change out a pulley in a few minutes rather than
changing to a different rear wheel sprocket and readjusting the
chain. The idea is to create more options.
 

DieselTech

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I helped 1 of the members on the forum do this already, he had the china tranny. But a Grubee pulley was a direct replacement for him, no machine work, no fiddling around to fit it. I cant remember what thread. But what you are wanting to do, is obtainable.
 

Sidewinder Jerry

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I helped 1 of the members on the forum do this already, he had the china tranny. But a Grubee pulley was a direct replacement for him, no machine work, no fiddling around to fit it. I cant remember what thread. But what you are wanting to do, is obtainable.
Just go to Find A Thread, click onto Threads With Your Post. Then look back through them; I do this often.
 

DieselTech

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They used to offer a 90 tooth rear driven spocket/pulley, I think that would be the sweet spot for me. I want to machine a shaft that will accept true 5/8 drive sprockets with the grubee pulleys. Then you open up tons of options.
 

DieselTech

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Staton used to offer & carry 15mm bore drive sprockets, that fit these trannys. I'm unsure if they are still offered or not. But that gave you the option to run anywhere from a 8tooth-14tooth drive sprocket.
 

Mike St

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I'm not sure if the Grubee pulley will fit exactly, but great if it
does. There is no place to get parts for the Chinese belt drive
with the 15mm shaft, so there's a need to find out if Grubee
parts can fill the gap. Very soon Bicycle-engines will run
out of 4 stroke parts and Grubee will be the only supplier. The
companies are running away from 4 strokes which I think is
a mistake because they're so much more reliable than
2 strokes, so I'd like to see max improvement of
Chinese 4 stroke designs, even if Americans have to
do it. I think Bicycle-Engines carries a 90T pulley with
a freewheel, here:
 

Nirve

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I have purchased a Grubee solid 80T pulley to convert the Chinese belt drive
drive from 5:1 (100T pulley) to 4:1 (80T pulley). This idea was suggested by
Nirve. This will raise the theoretical top speed from 26mph to 32 mph.
Instead of sanding down the shaft that the pulley goes on, I will remove
material from the pulley hole by hand, so the change is reversible. Can't
use a hone because of the keyway groove. Bicycle-Engines.com is
dropping 4 stroke kits and has the Grubee parts on a clearance sale.
Here's the part:
https://www.bicycle-engines.com/4g-...rocket-for-grubee-4-stroke-t-belt-drive-kits/
Also purchased a smaller belt for the 80T.
Hope it works out for you as well as it did for me!
It will fit most likely without sanding anything down. If it’s too snug, you can sand the shaft down just a thousand’, it will not affect the original fit to the 100t pulley, in my opinion.

I by the way was able to snug fit the Grubee pulley on to my Chinese shaft but I had the hardest time getting it off again. That’s really why I took off 0.1mm off the shaft.
 
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