And now for something completely different!!

[cloakedvillain]

The rim diameter on 20" wheels is around 16 inches, could definitely use moped rim ans tires if you wanted.

You can build up a custom wheelset: You'll want double walled aluminum rims. Steel will never run true. It will wobble at the spot welded seam.

You have to make a decision on the axle. There are hollow axles (QR and thru axle) or solid threaded axles. I recommend a freehub (cassettes not freewheels) no matter which style you choose.

8 speed altus rear derailleurs work very well and are very cheap. You can find these, new in box on ebay for 12-16 usd with free shipping. pair that with an 11-34 cassette, and a narrow wide chainring, and you will have decent shifting.

Some discussion on that ktm 50 engine here: Thread 'Next 2 stroke build idea.' https://motoredbikes.com/threads/next-2-stroke-build-idea.65139/

I think the internal reduction is 3.5:1 but I could have counted wrong.

 

[Pezz]

Still contemplating this build. . .

Some could rightly say going around in circles . . . . .

I wanted to build it rather light and would prefer 4T even though the KTM50 is a great option.

Also considering an internal gearbox's as apposed to the derailleurs a bit like Allen Millyard made about 20 years ago.


View: https://www.youtube.com/watch?v=S39oR_7Vwf8

 

[Gordy]

Maybe a CVT might fit this particular build a bit better. Gear boxes can get very expensive. Unfortunately light and four stroke don't tend to mix unless it's severely under powered.

Unless maybe you went with a honda ohv 50cc engine. Still under powered, but perhaps enough gears could get past that? I've seen people use the gear box from a motorcycle engine by running a cain to the crankshaft of the motorcycle engine, but that makes for alot of complexity and alot of vibration

 

[Pezz]

Maybe a CVT might fit this particular build a bit better. Gear boxes can get very expensive. Unfortunately light and four stroke don't tend to mix unless it's severely under powered.

Unless maybe you went with a honda ohv 50cc engine. Still under powered, but perhaps enough gears could get past that? I've seen people use the gear box from a motorcycle engine by running a cain to the crankshaft of the motorcycle engine, but that makes for alot of complexity and alot of vibration

Thanks for your input Gordy, I appreciate it

Agree with the low power engine means gears, lots of gears

Also considering the 79cc HF motor. Are they dimensionally smaller than the 212 for example?

Once I settle on the motor, I can look at the appropriate 'gearbox' options.

I had thought of a small capacity 2T gearbox with the cases cut off as they have self-contained oil supply.

As I want it light weight, I'm leaning towards deraillieur gears as I can get more ratios

 

[Gordy]

Thanks for your input Gordy, I appreciate it

Agree with the low power engine means gears, lots of gears

Also considering the 79cc HF motor. Are they dimensionally smaller than the 212 for example?

Once I settle on the motor, I can look at the appropriate 'gearbox' options.

I had thought of a small capacity 2T gearbox with the cases cut off as they have self-contained oil supply.

As I want it light weight, I'm leaning towards deraillieur gears as I can get more ratios

The 79cc from harbor freight is considerably smaller than the 212, but difficult to get more power out of.

 

[cloakedvillain]

The 79cc dimensions according to the retail website:

And the 212 dimensions:

A lifan 125cc pitbike engine would get you 4 speeds, about 8 hp and weight about 50lbs. Build using one: https://motorbicycling.com/threads/latest-lunacy-honda-ct70-clone-build.36108/

Here's a thread using a 2hp utility engine and a 3 speed hub: https://motorbicycling.com/threads/strange-brew.60263/

 

[Pezz]

Forgot about Motorbicycling and Im on there too

Just reading them now

I had thought of a sturney archer hub as an option.

 

[Pezz]

Well what have I been thinking lately???

Well I'm still contemplating engine options, as that is critical with this design.

Im going to run a jackshaft kit and derallieur with multiple gearing options

I like the flater engine as it has to sit under the frame.

The HP47 50cc motors are cheap and parts are plentiful. Like $130 on eBay

47cc and run reed valves.

Cant seem to find the bore and stroke for them though.

You can fit scooter barrels and piston kits and easily take them to 70cc's. Ease of mounting too

From talking to a friend who sells these motors they have very little issue with the bottom end. The weakness is the centrifugal clutch. Im sure I can find a suitable solution.

So a light 70-cc flat 2T is appealing.

Then I remembered I have a Sachs Dolmar 109 chainsaw motor I bought about 15 years ago.

43cc and 2.8HP from a piston port motor and built very strong. They also have a crankshaft driven oil pump and deliver oil from idle all the way to red line. Solid little motor. Will be a bit awkward to mount but doable.

I have been trying to find info on these Sachs motors online but not a lot around.

It is already orange

View: https://youtu.be/Gy54OnIUesA?si=X50vpohPjov8UQYu

 

[cloakedvillain]

Jerry likes the SRAM X3 and X4 but the shimano essa derailleur with the 11-45 cassette looks interesting. There are 5:1 actual gearboxes, and belt drive reduction gearboxes for that 76/78mm used by the cag engines and small utility engines in general.

 

[Will'smotobikes19]

I've wanted to do a build with a pocketbike engine for a while now. I don't know if the big bore is actually a big bore I still think they're 44mm just with a 2 piece jug. Bore is 44mm and stroke is 32mm. You'd have to put it on a rear rack or weld a flat plate on the frame to mount it. Pipe is not included either so you would have to buy it separate as cloaked said you can get different gearboxes for them. You need a 415 sprocket because cags come with like a 25h sprocket.