Pedal start for four strokes

frascati · #1 (**permalink**) 08-21-2009, 11:34 AM

Hey, I've been browsing all over the place getting ideas and noticed mention over the years and threads of, basically, how to get around pull starting the four strokes. The last thread I read was discussing electric starting options and petered out in the middle of 2008.

What about this? (bear with me, a drawing would be nice but beyond my computer talents at this point).

The motor is mounted within the triangle of tube (as conventionally) as close to the crankset as is mechanically possible. I haven't done any real experimenting yet so here's some very rough numbers for the sake of visualization. On the motors' pull start side is a 20 tooth sprocket. On the crankset, inboard (or outboard) of the chainring that drives the rear wheel is another chainring with sufficient diameter to come within about an inch of that 20 tooth sprocket on the motor and perfectly aligned with it.

Now the tricky description, but some of you might have already guessed. Take a, I don't know, pair of 14 tooth idler sprockets and a handful of 1/2 inch segments of steel rod of the exact diameter of the chain roller bushings and set the pile on your workbench. Now tig weld (everyone does that right?) the two sprockets together by aligning 14 (or is it 13? my head is starting to ache) of those steel rod segments into the valleys between the teeth and then spot welding (won't take much) each end into it's space. (god I need a picture).

There are a few ways of doing the above, heck, there might even be an off the shelf version of it some where, but I doubt it. But if you get the picture at all, you now have a "gear" to mesh together the 20 tooth sprocket on the motor with the very large sprocket on the crankset that is spinning (you're pedalling right now in your imagination, right?).

The idler "gear" that you've produced by following my very excellent instructions will be attached to a spring loaded arm and the arm attached to a lever at the handlebars such that while the crank is spinning (keep pedalling dammit) you can bring the "gear" down between the sprockets. The torque on your crankshaft sprocket and the resistance of the motor will suffice to capture the "gear" between the sprockets and maintain the mesh as long as there is resistance from the motor (compression, valve train, etc). And here's the beauty! As soon as the engine ignites, it will eject the "gear" from between the two sprockets, returning the "gear" on its arm back to the ready to start the whole shebang over again as soon as you're ready to start the whole shebang over again.

If I had a drawing it would be revealed to be a much much simpler and elegant solution than my tortured prose has suggested to pedal starting a four stroke motor with centrifugal clutch. Maybe I should have just waited until I'd tinkered this out and photographed it before burdening you all with such ravings. But I'd be interested to know if anyone has done this before, or if there is a yawning chasm in my thinking on this. Maybe it wouldn't actually work!

What do ya think?

restapukin · #2 (**permalink**) 08-21-2009, 05:28 PM

the science behind some of your questions was alluded to fairly recently ...let's see ... here, i think

Alternative/Doppleganger UNIVERSE discovered

you have to bear with what could be an imperfect translation from the german... it's not my field

frascati · #3 (**permalink**) 08-21-2009, 09:49 PM

touché mon ami!!!!!!!!!!!!!

but they missed "it ignites! it ignites!"

tyrslider · #4 (**permalink**) 08-21-2009, 10:57 PM

I dig it! You'd likely need the wide spindle and a special chainring mount on the Honda and clone 'cause even w/ the pull start out it's pretty wide. Looking at it now the way that mine lines up if I had a chain ring on the crank arm I'd be able to line it up, no problem!

NEAT TIMES · #5 (**permalink**) 08-22-2009, 12:17 PM

Frascati, How About Putting A Small Drive Sprocket On The Right Side Of The 4 Stroke Motor (where The Pull Start Was). Then Run A Chain Down To Sbp Freewheel Crank Set Up. You Would Have Your Pedal Start And A Shift Kit Without The Need For The Jackshaft. Anybody Have Comments?? Ron .

tyrslider · #6 (**permalink**) 08-22-2009, 01:52 PM

Gearing to the pedal crank on my 4 stroke shifter is about 31.2:1 (I need to reduce mine a little more 35:1 ish). Unlike a single speed bike that is reduced 16:1 ish, your pedal crank to rearwheel is geared up i.e. multiplied (typical cruiser 1 speed is 48/18 or 1:2.666, 1 crank rotation = 2.666 wheel rotations). So on a jackshaft set up you need to reduce engine speed much more 'cause at the pcrank you gear it back up again.

You would need a 315 tooth chainring for a 9 tooth op sprocket.

Good thinking though! And I still love the pedal start Idea though the only benefit I see is a slightly narrower motor.

NEAT TIMES · #7 (**permalink**) 08-22-2009, 02:08 PM

Tireslyder, Hi. Lol. Jim Can Make You A 315 Tooth Sprocket. Ha Ha. How About Gaining Back The Gear Ratio By Using A Internal Shifter Hub And Use A Big Sprocket On The Rite Side Of The Rear Axle. Bolt It To The Stock Sprocket. I Bought A Royce Cruiser Yesterday With The 4 Spd Internal Hub, Rear Rack, Cable Lock , Water Bottle, Bran New Condition =45 Bucks. Its So Purdy. METALIC CHARCOAL BLACK. RON .

frascati · #8 (**permalink**) 08-22-2009, 03:27 PM

And just what is wrong with a 315 tooth sprocket at the crank?

I see it as another means of propulsion

You'd just need smaller shoes for the sprocket teeth.

NEAT TIMES · #9 (**permalink**) 08-22-2009, 04:43 PM

Lol, Ha Ha. I Surely Think You Are Missing More Than A Shoe!! (pic) Ron .