Flathead Honda build- it’s happening

[Yellow Perch]

Ok guys I’m back after a year lol, I’ve got the Honda, and I’m ready to start my build. I’ve gained a lot of mechanical skills in the last year so I think I’m ready to tackle it. I’m starting out with a steel frame bike, and I’m making my own motor mount with angle iron and sheet metal. The Honda g100 runs good but needs an oil slinger, probably will have to replace the connecting rod assembly as a whole. I’m going to fabricate a throttle linkage, but I am not sure what to do for a transmission, the bike I’m using has too small of a rear hub so I’ll probably have to go with the rag joint setup for a sprocket...
going to be a fun project

 

[5-7HEAVEN]

Welcome back, Yellow Perch.
Lotta builders use Torque Convertor(TC) system.
Mount your engine first, then see if you have room.
Remember that the TC multiplies your rear wheel gearing about 2.7 times, then reverts to 1:1 or less.
So, if you use a 12tooth(12t) jackshaft gear and a 48tooth(48t) rear wheel combination, that's (48/12) x 2.7 = 10.8:1 at a standstill.
However, when the TC upshifts, you've only got 4:1 gearing, which is too high for your G100 engine.
So, you'd have to go with TC, plus a large 72t wheel sprocket and a 9t-12t jackshaft sprocket,
which gives you 8:1, 7.2:1 or 6:1 final drive, when the TC upshifts..
Orrr, you could use all sprockets with a jackshaft:
12t sprocket on the clutch chained to a 24t at the jackshaft,
then 12t jackshaft to a 48t wheel sprocket.
That gives you 24t/12t = 2:1; 48t/12t = 4:1.....
2 x 4 = 8:1.....
If that's too stiff, replace the inboard 12t with a 14t sprocket.
2 x (48t/14t) = 6.86:1.....
or an inboard 16t to get 2 x (48/16) = 6:1 gearing.

I'm building a 212cc bike. However, I'm using pulleys, belts, a jackshaft and a 7-speed bike gears.
My 7th gear will be 6.34:1.

 

[Yellow Perch]

Welcome back, Yellow Perch.
Lotta builders use Torque Convertor(TC) system.
Mount your engine first, then see if you have room.
Remember that the TC multiplies your rear wheel gearing about 2.7 times, then reverts to 1:1 or less.
So, if you use a 12tooth(12t) jackshaft gear and a 48tooth(48t) rear wheel combination, that's (48/12) x 2.7 = 10.8:1 at a standstill.
However, when the TC upshifts, you've only got 4:1 gearing, which is too high for your G100 engine.
So, you'd have to go with TC, plus a large 72t wheel sprocket and a 9t-12t jackshaft sprocket,
which gives you 8:1, 7.2:1 or 6:1 final drive, when the TC upshifts..
Orrr, you could use all sprockets with a jackshaft:
12t sprocket on the clutch chained to a 24t at the jackshaft,
then 12t jackshaft to a 48t wheel sprocket.
That gives you 24t/12t = 2:1; 48t/12t = 4:1.....
2 x 4 = 8:1.....
If that's too stiff, replace the inboard 12t with a 14t sprocket.
2 x (48t/14t) = 6.86:1.....
or an inboard 16t to get 2 x (48/16) = 6:1 gearing.

I'm building a 212cc bike. However, I'm using pulleys, belts, a jackshaft and a 7-speed bike gears.
My 7th gear will be 6.34:1.

I like the CVT idea, but since the motor is only like 2hp I’m afraid of how much power it would rob. Another option I was considering is somehow making a jack shaft to be able to use the rear gears but then I’d need a free wheel setup and that would be expensive. What would be the best option for a centrifugal clutch/ jack shaft single speed setup?

EDIT: I am planning on doing a couple mods like fabricating an adapter to use a pod style filter, as well as a different exhaust setup. I have literally 5 carbs for this motor so I can do some experimenting with drilling out jets to get more fuel. I was also planning on removing the governor, not sure how many rpms are safe to run a flathead at but I figure the valves will float before it blows

 

[Will'smotobikes19]

just got a g100 from my neighbor need to fix the carburetor and pressure wash it. Has some patina on the fan shroud. Thinking it would be cool on my OCC chopper.

 

[Will'smotobikes19]

Guys is it alright if the flywheel side main bearing moves in it's socket, I can still see the balls free in the bearing. does the crank push the bearing housing firm with the sidecover? what is the value of the older Honda Flatheads? thinking of rebuilding it. A little pitting on the camshaft and some wear but it's in ok shape. I have estimated repair cost at $38.57, motor came in a package deal of 3 engines for $40. Is it worth it?

 

[Frogslayer]

Just my opinion, if the engine is the look you want I'd rebuild the one you got then you know what you got instead of looking for another Honda flathead. If you just need something to drive a wheel I'd probably go new myself. More expensive but also ridiculously good reliability and really really great fuel economy. Quiet and smooth. As much as I love to shout 'MERICA while popping off rounds over the hood of my 4wd, there's no denying how awesome the people at Honda are at designing then executing the design to strict high quality and very tight tolerances while using good materials and the end result are some of the best power plants that can be found on the planet.

 

[Chainlube]

Guys is it alright if the flywheel side main bearing moves in it's socket, I can still see the balls free in the bearing. does the crank push the bearing housing firm with the sidecover? what is the value of the older Honda Flatheads? thinking of rebuilding it. A little pitting on the camshaft and some wear but it's in ok shape. I have estimated repair cost at $38.57, motor came in a package deal of 3 engines for $40. Is it worth it?

Is the bearing moving or is the crank loose on the bearing? If the bearing is moving then the hole will have to be resized and a bigger bearing put in, if it's the crank, then a new bearing will shore everything up.

 

[Will'smotobikes19]

My G100 is blowing white smoke after honing. I think it needs new rings or the oil ring is stuck.

 

[Chainlube]

My G100 is blowing white smoke after honing. I think it needs new rings or the oil ring is stuck.

Are you saying you took it apart and honed the cylinder and never changed the rings while you were in there? Tsk tsk.

 

[Will'smotobikes19]

Yes, my cousin said it needs new rings $15 so I guess i'll get them.