a shadetree briggs flyer build,

[the13bats]

Yes, correct, the dolly bike had a 212, the 212 is the go to because like with everything some people think more is better, ive seen adult trikes with it, i dont know how fast they are going but its too fast to be stable or stop correctly,

I belive the 79 is about perfect for many things, not to physically large, not too heavy, its drawback is the basically non adjustable carb, im sure a better carb will bolt on i havent hunted it,
Ill look again at paperwork pretty sure mine was rated 3.5 but it's an older one, i might have looked at fpt,

Back in the 70s most go karts and mini bikes had the old 3.5hp engines and went 15 to 25 mph, they were made for a back yard or lot, people want 50mph and go huge engines asking to get hurt, badly
Now especially with all the imported toys things are fast, not necessarily designed to be safe goung that fast, doesnt matter, buyers want fast and yell "hey yall watch this".
Very few 2 wheelers i see around here are anywhere close to being safe going that fast, rant over, lol.

So on your 79 bike what drive train did you have?
Recall the sprocket sizes?

 

[Will'smotobikes19]

https://www.gasbike.net/products/79cc-transmission-for-predator-engine-4-stroke
https://www.ebay.com/itm/40-Tooth-C...779825&hash=item3f9509e010:g:FaoAAOSwny1akYYp I'm pretty sure that transmission has a higher price than it used to. You wouldn't really need it in your application it has a jackshaft so the chain lines up with the rear bike wheel. You could probably just use the clutch part. I might put the 79 on a mini chopper I have. It has a little 49cc engine and it was electric start.

 

[the13bats]

I posted in the drive line section, i need to learn more about transmissions and gearing,

In basic form a trailer pusher which i am interested in is a mini bike with no front forks/wheel,

I havent seen one yet that places drive wheel ahead of engine,

It doesnt much matter what its pushing besides the weight its trying to push,

In my case or a trike with two rear wheels my connection, trailer to bike will be much um, cleaner looking,
Of the above pics i like the little one best,
But note, none run a transmission, just direct engine to wheel drive,
Youtube videos show most pushers faster than what im seeking....

 

[curtisfox]

You are right, and the gearing doesn't change by moving the wheel ahead. LOL In fact the engine out back will give more weight transfer, traction on the wheel. If you are still in the undesired thought about gearing. A lot of old mini bikes had jack shaft, and could change the center sprockets for different gearing. Say like from the clutch to 16 tooth then 10 to rear wheel, just changing the 16 bigger or smaller will make a difference. .............Curt

 

[the13bats]

I lkely worded it oddly but i meant gear rations dont change if the drive sprocket is on the axle or wheel hub and do not care if engine is in front, top or rear mounted.

Okay a jackshaft is a version of the so called transmission offered for the 79cc.

So heres where you can help me understand gearing/ratios

Lets say our clutch is 10 tooth drive sprocket 60,
And we have a jack shaft with 10 tooth on each end, one driven by the clutch the other chain driven to our drive sprocket, in that scenario the jack shaft has zero effects on ratio,

But lets say for whatever reason we cant run a 60 tooth drive sprocket, we want to run say 30 tooth,
We want to keep the 10 tooth clutch,
What size gears, would we run on the jack shaft, to make this happen,
we will call one end clutch the other load,

Now of course either js end gear can be chanhed and likely more thst one way to get our 10tooth clutch 30tooth drive but keep that 60 to 1 we had with the 60 tooth drive,

Thanks for any help,
Cheers
b

My dad passed in 2014 at 89 but he was a retired navy plane tech and machinist, he was a top go kart racer in the late 50s early 60s,
The stuff i asked above he would whip right out of his head, he always had a little pad and pen and would draw it right up, i miss him.

 

[curtisfox]

You got it all right, for the most part. 60 divided by 10 = 6 to 1
30 divided by 10 = 3 to 1 double that with the shaft you get your same 6 to 1. But your wheel will have to have bigger sprocket as not to many bolt on's sizes for the wheel. Here is a gear ratio chart you can play with. http://jimsitton.net/ratiocalc/

Check out Northerntool.com they have some go kart parts cheaper, Glad to help just ask LOL...........Curt

 

[Old Busted Hotness]

Lets say our clutch is 10 tooth drive sprocket 60,
And we have a jack shaft with 10 tooth on each end, one driven by the clutch the other chain driven to our drive sprocket, in that scenario the jack shaft has zero effects on ratio,

But lets say for whatever reason we cant run a 60 tooth drive sprocket, we want to run say 30 tooth,
We want to keep the 10 tooth clutch,
What size gears, would we run on the jack shaft, to make this happen,
we will call one end clutch the other load,
.

Basically, you need to introduce a 2:1 reduction in your jackshaft. So you'd substitute a 20t sprocket on the clutch end while keeping the 10t on the load end.

10t clutch to 20t jackshaft input=2:1
10t jackshaft output to 30t wheel sprocket=3:1
2x3=6:1 overall. You'll want to run a pretty small wheel to make that work.

When I raced RC cars, we'd set gearing by calculating the "rollout, " or distance travelled per motor revolution. Wheel diameter x pi gets you distance per wheel revolution, divide that by your reduction to get distance per engine/motor revolution. Then multiply by rpm to get your projected speed. Example:
26" wheel diameter x pi (3.1416) = 81" per wheel rev
Divide by 12= 6.81 feet/wheel rev
Divide by 20 (typical MB ratio) = 0.34 feet/engine rev
Multiply by 7000 rpm = 2382.4 feet/minute
Multiply that by 0.0113 (ft/min to mph) and you get 27 mph

Substitute your own numbers for wheel diameter, engine rpm and gear ratio and you'll find out how fast you'll go for a given setup. Easy!

 

[Old Busted Hotness]

And if you're using a 10" dolly wheel with a 6:1 drive ratio and a 3500 rpm engine, you're going 17.25 mph.

 

[curtisfox]

Basically, you need to introduce a 2:1 reduction in your jackshaft. So you'd substitute a 20t sprocket on the clutch end while keeping the 10t on the load end.

10t clutch to 20t jackshaft input=2:1
10t jackshaft output to 30t wheel sprocket=3:1
2x3=6:1 overall. You'll want to run a pretty small wheel to make that work.

When I raced RC cars, we'd set gearing by calculating the "rollout, " or distance travelled per motor revolution. Wheel diameter x pi gets you distance per wheel revolution, divide that by your reduction to get distance per engine/motor revolution. Then multiply by rpm to get your projected speed. Example:
26" wheel diameter x pi (3.1416) = 81" per wheel rev
Divide by 12= 6.81 feet/wheel rev
Divide by 20 (typical MB ratio) = 0.34 feet/engine rev
Multiply by 7000 rpm = 2382.4 feet/minute
Multiply that by 0.0113 (ft/min to mph) and you get 27 mph

Substitute your own numbers for wheel diameter, engine rpm and gear ratio and you'll find out how fast you'll go for a given setup. Easy!

Right on: Thanks for setting it straight, been many years seance doing gear ratio thinking. Should of known as mini bike has that type of setup. ...........Curt