Transmission options for flathead Honda G100

Yellow Perch

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Jul 7, 2017
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There are sleeves made to use the 3/4" cvts with a 5/8" shaft. A properly aligned cvt with a new belt might lose 10% power at the most, and roughly 5% if perfectly aligned and tensioned. A properly aligned chain that isn't worn is around a 5% loss. So with a cvt and secondary chain to the back you are looking at a 10%-30% loss depending on tension, alignment and wear.
So about .75 hp loss? Would that make a difference. I am fairly light so maybe that would make up for it... I will look at the sleeves tomorrow. I have seen the torqaverters for about $60 but the reviews say there is a problem with the rear shaft having a lot of play and no way to shim. Is there a particular series or model i should look for? They all seem to have different specs and engagements and such. So many options!!!
 


CrazyDan

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Jul 9, 2016
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So about .75 hp loss? Would that make a difference. I am fairly light so maybe that would make up for it... I will look at the sleeves tomorrow. I have seen the torqaverters for about $60 but the reviews say there is a problem with the rear shaft having a lot of play and no way to shim. Is there a particular series or model i should look for? They all seem to have different specs and engagements and such. So many options!!!
I would look at a closer to a .5 hp loss. There are the real deal and many knockoffs. Seems the knockoffs crack on the plate at the same spot. Engagement speeds are adjusted with springs and weights.
 

The_Aleman

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May 2, 2007
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I would suggest using a standard jackshaft plate, decent clutch, and shoot for an overall ratio at least 10:1 (if you're using 26" wheel)

Maybe something like this:

Easy to play around with gearing with those, but they have been known to chatter off the line if you're geared tall and have a cheap clutch. You can just figure out what wheel sprocket you want to run and then choose what gear you want on the plate. The Honda G100 supposedly has 3 different versions according to engine-specs.net ranging from 76CC to 98CC. All are very low compression flathead engines, but can be made to be quite torquey if you can raise the compression. The Lifan 2.5 is pretty much an updated clone of the G100K2, as far as mounting options.


You'll have to figure out which G100 you actually have if you want to know the actual power it makes.
Edit: It's a solid, honest engine, but isn't a powerhouse out of the box. Easy to mod, tho.
 
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mark20

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Sep 26, 2018
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531
well, ill help you out,
for my build i used a baja warroir gear reducer (its a 3:1 or a 8:1, i cant quite remenber)
and check your shaft diameter. mine was 5/8ths, i used a amazon clutch (make sure its 5/8s id, and that it accepts 41, 40, and 420 chain)
i them bought a 56t rear sprocket as the 44t is a bit short handed (but if you are going to leave the govener, please use the 44t)
my engine is a flat head, so i bypassed the govener (ill let you do that, you just replace the spring with the wire) i welded up my own motor plate.
also, this is not going to be that much faster than a stock china girl, but its going to be 100X more reliable, and cheaper to run. main reason i did it. (ive gotten up to 42 mph, so)
and there you go! you have a reliable, and problem free engine build!

EDIT: go to the second page on the 4 stroke engines page, the threads called "97cc engine swap!"
(if you need anymore help, just ask)
 
Last edited:

Yellow Perch

Member
Joined
Jul 7, 2017
Messages
126
well, ill help you out,
for my build i used a baja warroir gear reducer (its a 3:1 or a 8:1, i cant quite remenber)
and check your shaft diameter. mine was 5/8ths, i used a amazon clutch (make sure its 5/8s id, and that it accepts 41, 40, and 420 chain)
i them bought a 56t rear sprocket as the 44t is a bit short handed (but if you are going to leave the govener, please use the 44t)
my engine is a flat head, so i bypassed the govener (ill let you do that, you just replace the spring with the wire) i welded up my own motor plate.
also, this is not going to be that much faster than a stock china girl, but its going to be 100X more reliable, and cheaper to run. main reason i did it. (ive gotten up to 42 mph, so)
and there you go! you have a reliable, and problem free engine build!

EDIT: go to the second page on the 4 stroke engines page, the threads called "97cc engine swap!"
(if you need anymore help, just ask)
My motor is a 5/8" shaft. I am planning to remove the governor altogether. You say the 44 tooth is short handed, meaning it is geared too high? I found a generic 4 stroke mounting plate online that I am planning to modify to fit my particular motor. I am hoping for about the same speed as you got, do you still have yours? I am also looking for a bike to put it on...

EDIT: I cannot seem to find the baja warrior reduction you were talking about, they are all missing parts.
 

Yellow Perch

Member
Joined
Jul 7, 2017
Messages
126
I would suggest using a standard jackshaft plate, decent clutch, and shoot for an overall ratio at least 10:1 (if you're using 26" wheel)

Maybe something like this:

Easy to play around with gearing with those, but they have been known to chatter off the line if you're geared tall and have a cheap clutch. You can just figure out what wheel sprocket you want to run and then choose what gear you want on the plate. The Honda G100 supposedly has 3 different versions according to engine-specs.net ranging from 76CC to 98CC. All are very low compression flathead engines, but can be made to be quite torquey if you can raise the compression. The Lifan 2.5 is pretty much an updated clone of the G100K2, as far as mounting options.


You'll have to figure out which G100 you actually have if you want to know the actual power it makes.
Edit: It's a solid, honest engine, but isn't a powerhouse out of the box. Easy to mod, tho.
What type of mods? Other than a governor removal I cannot seem to find any performance parts for my motor? It does have some kind of straight pipe muffler on it, its very short (about 4 inches) not sure if the motor is just old or someone put it on later... How could I raise the compression? I am getting this motor from a gokart track where it sat unused on the shelf for many years. I am not sure why it was shelved, hopefully nothing serious. I split the case and the internals look good. How many PSI compression will it have stock?

EDIT: Pretty sure my motor is a 98cc
 
Last edited:

mark20

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Sep 26, 2018
Messages
531
My motor is a 5/8" shaft. I am planning to remove the governor altogether. You say the 44 tooth is short handed, meaning it is geared too high? I found a generic 4 stroke mounting plate online that I am planning to modify to fit my particular motor. I am hoping for about the same speed as you got, do you still have yours? I am also looking for a bike to put it on...

EDIT: I cannot seem to find the baja warrior reduction you were talking about, they are all missing parts.
yup!
mine is a diamondback sorrento xxl bike.
and yes, that meant its geared WAYY to high with a 44t.
i had a baja warror mini bike, i converted it to a cvt drive when i got it, and that gear reducer was a spare part.
but if you cant get it, then go with a billet one ( its very expensive, so a china girl might be the way to go)
 

Yellow Perch

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Joined
Jul 7, 2017
Messages
126
yup!
mine is a diamondback sorrento xxl bike.
and yes, that meant its geared WAYY to high with a 44t.
i had a baja warror mini bike, i converted it to a cvt drive when i got it, and that gear reducer was a spare part.
but if you cant get it, then go with a billet one ( its very expensive, so a china girl might be the way to go)
would a clutch to jackshaft be a better option than a cvt? My motor makes less horsepower and torque than a HF predator 79cc and even that motor people say to stay away from a torque converter...
When you say a china girl is the way to go do you mean a 2 stroke kit? I have the motor already so I want to work with what I have...
 

mark20

Active Member
Joined
Sep 26, 2018
Messages
531
would a clutch to jackshaft be a better option than a cvt? My motor makes less horsepower and torque than a HF predator 79cc and even that motor people say to stay away from a torque converter...
When you say a china girl is the way to go do you mean a 2 stroke kit? I have the motor already so I want to work with what I have...
yea, when i say china girl i mean those 80$ 2 stroke kits.
if you already have the motor, its going to cost you more than a entire new kit. (even those 4 stokre kits are cheaper than building your own, there like 160$)

i built my own becuase it was cheap for me. (it cost me only 50$ to do the conversion) and i had a 2 stroke kit before. i used most of the parts from it.


heres the bike before i got the 4 stroke engine.
 

Yellow Perch

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Messages
126
yea, when i say china girl i mean those 80$ 2 stroke kits.
if you already have the motor, its going to cost you more than a entire new kit. (even those 4 stokre kits are cheaper than building your own, there like 160$)

i built my own becuase it was cheap for me. (it cost me only 50$ to do the conversion) and i had a 2 stroke kit before. i used most of the parts from it.


heres the bike before i got the 4 stroke engine.
I appreciate the advice, but I would rather not have to deal with crappy chinese engines. Honda is the best of the best and I'd like to continue with it. Its worth spending a little more to get a reliable bike...
Anyway would a clutch to jackshaft be a better option than a cvt? My motor makes less horsepower and torque than a HF predator 79cc and even that motor people say to stay away from a torque converter...
 
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