4 Stroke Engine basics

[Timbone]

Well I'd get a clutch you can put weaker springs on, but that's from somebody who weighs more than 200lbs, you are a much smaller looking person and 140cc is a decent chunk of power, 16mph may be OK, just expect that clutch to taper away faster since it's a bit of a high number all things considered.

The torque-a-verter would be a solid idea, it would really distribute that power nicely for you and it shifts automatically. Are you using this on the road or off? If you have any plans with traffic you really should use a larger gear and get engagement at a lower speed if you keep a single speed set up.

This will be for road use (gonna try to plate it!!!). I had to give up the long distance cycling so I am closer to 200 lbs these days. If I single gear it, I’ll invest in a really good centrifugal clutch. As I told another helpful poster, I am unsure what bolting the CVT on would look like. Would probably have to drill 4 holes and it would conflict to some degree with my motor mount plan.

Sounds like a 2200 RPM engagement with an overall 9.1 to 1 reduction would be on the margin. Thanks!

 

[Will'smotobikes19]

Go powersports sells a made in US 3/4 clutch for #410 or #415. I suggest getting a #415 non oring from regina chain its better quality than chinese and similar price its made in Italy. Way less play right out of the package it will last longer.

 

[Timbone]

Im trying to picture that swingarm with a jackshaft built in. Maybe one of the 79cc transmissions could bolt up the holes are slotted just with a 3/4 clutch instead of 5/8 there is a jackshaft built into the 79 transmissions. My next build is going to ve a 2 stroke instead of the gx120 build.

Here’s a pick of my current ride with jackshaft swingarm. Solid 1/2” hard steel axle. Bushings interface the swingarm end connections and the gear cluster offset.

I was welding on my new swingarm design earlier: gonna make it out of a steel front fork. Chopped off the two arms perpendicular to the fork legs. Gonna weld in two thick round metal spacers to widen the fork to about 7”. The stem of the fork will be drilled out and strengthened as necessary to be the swingarm interface. Mostly likely, I’ll run a 1/2” spinning axle jackshafting the motor chain to the right. I really like the idea of of the spinning axle rolling right thru the swing arm connected via a couple of good sealed bearings.

I’ll post pictures as I move forward.

2 stroke build is pretty straightforward and cheap. With a good carb, a good CDI, and a hub adapter you’ll have a solid machine with few breakdowns. Good luck and have fun!

 

[Will'smotobikes19]

Thanks it will be somewhat of a high performance build I bought a 3mm stroker crank and a 48mm bore iron sleeved jug as well as the cnc saucer type high compression head, ngk plug, italian chain and the ebay kit. I already have a 1.5 cnc hub adapter just need a sprocket. Probably go with a 36t steel.

 

[GreenMantis]

One issue you might encounter is that your engine might end up running too lean, and you might have to put larger jets in your carburetor. Engines with centrifugal governors are usually jetted too lean for a free throttle arrangement. They are meant to only run at one speed, without any sudden changes in throttle position. I know this is true for the 50cc engines. The Huashengs work great, since they account for that, and put bigger jets in them. But the genuine Honda GX50's always run too lean. It's not a big issue, but it'll be a lot easier to deal with if you expect that in advance.

 

[Timbone]

One issue you might encounter is that your engine might end up running too lean, and you might have to put larger jets in your carburetor. Engines with centrifugal governors are usually jetted too lean for a free throttle arrangement. They are meant to only run at one speed, without any sudden changes in throttle position. I know this is true for the 50cc engines. The Huashengs work great, since they account for that, and put bigger jets in them. But the genuine Honda GX50's always run too lean. It's not a big issue, but it'll be a lot easier to deal with if you expect that in advance.

Excellent input! I’ll keep this in mind!

I’ve decided to go with a CVT. It will be the best investment of money and will actually simplify my rear swingarm design.

Thanks!

 

[GreenMantis]

I bought a comet clone on ebay for $60. It's probably not as good as the original, but for $60 it's more than good enough. Don't search "CVT" for some reason, they like to call them "torque converters". They are like a CVT in almost every respect, except that they will open up all the way, and have a bushing around the shaft, such that it doubles as a centrifugal clutch by releasing the belt completely on the driven shaft, so it doesn't need a clutch like the CVT's on 50cc scooters do. It's pretty neat.
https://www.ebay.com/itm/Go-Kart-To...384646?hash=item48a2d308c6:g:R5AAAOSwQwZaeVtr

I should put out one small disclaimer, I sort of stalled on the project I bought this for, I haven't put it all together, much less tested it out, or anything..... yet. But I still appreciate the way it works, even if I haven't actually used it, yet.

 

[Will'smotobikes19]

I heard some briggs and stratton parts are made in china. Idk if that's true or not but without that governor hopefully the rod doesn't snap. The go kart people usually put billet rods in the race engines. I could probably put something together with the vertical shaft motor I have. Its a 158cc briggs I'm busy with the 2 stroke build though gonna go to the hardware store and replace all the chinese bolts and see if they have 6202 bearings.

 

[Timbone]

I am going with one of those Torq A Verters. TAV2 looks pretty solid. Hooking that up would be a breeze!

 

[GreenMantis]

Yeah, I thought you might like those. Especially when you said you really didn't want to drop $250 for one, neither would I, but that TAV2 is perfect, and probably exactly what you want, and they are a deal for $60. And the way they set up the pattern of the holes on the mounting plate, you can bolt one onto just about any engine, and at any angle relative to the engine that you want to. They are very versatile. They come in 3/4" and 1" shaft sizes, I think you said your output shaft is 7/8" and that you would turn down you shaft if you had to: You don't, then go with the one inch TAV2 kit, and find piece of steel tubing with a 7/8" ID and 1" OD and 1/16" walls, and use that as a sleeve. Cut a slot through it to clear your woodruff key. The worst that can happen is you might have to find a larger woodruff key that can span the extra distance. That is the easy, and the right way to make that work.