Now I have a 79cc Harbor Freight 4-stroke. Next step please?

[wayne z]

Well, sometimes old school materials just do the job. He experimented with everything possible to use for a drive roller. The problem is to get something that doesn't slip when wet and doesn't wear the tire. Turns out that hardwood works better than all other materials that he worked with.
Myself, I made a knurled steel roller that worked very well wet until the knurls quickly smoothed themselvs down.

A plain steel roller works excellent when dry, and still works wet if you're careful with the throttle.
I did experiment with a grindstone roller. It never slipped even in muddy roads, but the tire wore out in about 100 miles.

The most important thing you can do to make a friction drive work more effectivly and efficently is to use as large of diameter roller that you can get away with.

I would discard the spring loaded rack idea, and figure out a way to mechanicaly adjust the rack for roller pressure. Maybe a couple of turnbuckels attached to struts at the rear of the rack? Spring loaded like your drawing, will allow the engine and rack to bounce around on road bumps, and prolly just the weight of the whole assembly will depress the roller too much. On my 3.5" roller I never needed any more than 3/16" tire deflection with the smooth roller for good grip.

 

[Nehmo]

...
The most important thing you can do to make a friction drive work more effectivly and efficently is to use as large of diameter roller that you can get away with.
.

If it's true that rubber grabs the shaft effectively, then what about hockey pucks?

 

[wayne z]

If it's true that rubber grabs the shaft effectively, then what about hockey pucks?

I was referring to the roller grabbing the TIRE effectivly. Whatever you decide to use has to be mechanicly secured to the shaft, so, type of material has not much to do with grabing the shaft.

Some people have used hockey pucks sucessfully if I remember correctly.

I think McMaster Carr sells flat rubber and steel finished bore pullies with a keyway and setscrew.

 

[Nehmo]

... I would discard the spring loaded rack idea, and figure out a way to mechanicaly adjust the rack for roller pressure. Maybe a couple of turnbuckels attached to struts at the rear of the rack? Spring loaded like your drawing, will allow the engine and rack to bounce around on road bumps, and prolly just the weight of the whole assembly will depress the roller too much. On my 3.5" roller I never needed any more than 3/16" tire deflection with the smooth roller for good grip.

Using adjuster screws to fix the compression-pressure of the roller to tire would make the lift-clutch unusable.
Actually, I was estimating the pressure needed by statements Cannonball2 made,"...but still would slip on steep hills. So I began to increase down pressure, way higher than the rubber rollers required. finally I hit a point that would hold the engines torque. It requires a LOT of down force, right to the point that the lift clutch is getting pretty hard to pull, but still useable in frequent clutching situations like traffic...."

I bought 2 0.5" bore pillow block bearings at $22 each from Grainger.
At this point, I'm considering making the apparatus from 2 pieces of 1"x1" square steel tubing.

 

[Nehmo]

I bought a couple of pieces of 1"x1" square steel tubing to form the rails of the "ladder"(shape of the mounting apparatus). The cross members can just be long all-thread bolts with nuts and washers.
I plan on making an angular bend in the ladder by cutting out V sections and welding (have to borrow a welder) together after bending.
The roller shaft is 0.5" diameter.
Currently, I'm inclined to using 2 hockey pucks as a roller. I'm considering drilling a hole across the diameter of the shaft. I can then put a nail with a cut off head through a puck and through the hole in the shaft. That should hold the puck.
I'll put fender washers and shaft collars on both sides of the 2 pucks.

 

[Nehmo]

This is my idea for the roller.

I drill a hole through the shaft and place & glue (for assembly) a 2" long x 0.125" diameter pin through the hole in the shaft. Then, with shaft-diameter-size holes drilled in the centers, I place 2 hockey pucks on both sides of the pin. I then make holes in the pucks and bolt them together, compressing around the pin.

Is a 2-puck wide roller enough? With my current plan (of placing the roller between the ladder), there's not room for a 3-puck roller, but I could change that.

 

[wayne z]

That's a great idea about sandwiching the pin with 2 pucks to connect the shaft to the roller!

How wide will it be with 2 pucks? As long as it is as wide as the tread of the tire, you should be fine. A 2.25 tire has a tread width that is somewhat less than the tire width, so you should be fine with 2.

 

[Nehmo]

Rails:
Using 2 pieces 32" long 1"x1" square steel tubing, I cut V-sections (about mid length), bent to close the Vs, welded together to form pieces with an obtuse angle. Drilled several holes to accommodate different trial positions of the engine, bearings, and pivot.

Roller:
Using 2 1" thick 3" diameter hockey pucks, I drilled the center holes for the shaft. I also drilled 2 small holes on both sides of the center for the sandwich bolts.

Shaft:
I drilled one hole perpendicular to the length of the shaft to hold the securing pin. I had planned to use a roll pin, but the right size wasn't immediately available. I found a 2" long piece of all-thread to use.

Pivot:
I plan to use a 3/8" bolt through a bushing set in a seatpost-brace part of the bike frame.
Bolt head - left rail - spacer - bike frame - spacer - right rail - nut & locknut

Yet to do:
I still need the shaft pulley. A 3" one gives an overall ratio of 16.5:1.
Need to devise a system of levering the clutch, perhaps simply an extension of the rails forward of the pivot.
Need belt.
Need arrangement for throttle.
Need to wire up a kill switch someplace accessible.

I've experimentally assembled the ladder using the engine mounting plate without the engine. I can see now that the rack behind-seat engine position interferes with the rider mounting the bike.

 

[Nehmo]

I'm close to getting the drive-system functional.
(It's difficult to see in this pic, but the hockey pucks are mounted on their shaft.)
Regarding the throttle control, I'm thinking an old brake hand lever has enough travel in the cable to work as the control. Should I just use one of those attached to a cable attached to the existing on-engine lever attached to a return spring?

 

[wayne z]

Lookin' real good!
Yes, a brake lever and cable will work fine. Go back to post # 24 in this thread and blow up the pic, and also study the text to see how I did it.
Pretty simple, and it bypasses the internal govenor. The govenor is very unneccessary on a motorbike.

 

[Nehmo]

I mounted the engine today. I still need a belt, the throttle linkage, the kill switch mounted on the handlebars, and a piece of steel connected as a clutch lever.
Also, I need to route the exhaust differently. As it is, it blows forward.

Naturally, I'm designing improved-prototype #2 as I go. I'm considering placing the engine completely behind the rear wheel and using a rocker arm (pivoted on the same axis as the engine crank shaft) with 2 rollers to give 2 ratios. It's a thought.

 

[wayne z]

I mounted the engine today. I still need a belt, the throttle linkage, the kill switch mounted on the handlebars, and a piece of steel connected as a clutch lever.
Also, I need to route the exhaust differently. As it is, it blows forward.

Naturally, I'm designing improved-prototype #2 as I go. I'm considering placing the engine completely behind the rear wheel and using a rocker arm (pivoted on the same axis as the engine crank shaft) with 2 rollers to give 2 ratios. It's a thought.

I like the idea of 2 rollers for 2 ratios. Great idea! Be better though for balance if you could get the motor CG at least right over the rear axle if not a little ahead.. Maybe 2 jackshafts with 1 roller ahead and 1 behind the motor?

 

[Nehmo]

...Be better though for balance if you could get the motor CG at least right over the rear axle if not a little ahead...

I'm embarrassed to admit this publicly, but for a while I used an electric-bike with lead-acid batteries. (And this experience begets my primary piece of advice to someone contemplating an e-bike: Don't use lead-acid batteries under any circumstances. Yes, they are commonly used in internal combustion cars and trucks to supply the starter, lights, and ignition {SLI}, but even that use is technologically obsolete) It weighed 53 kg (117 lbs) without 100 kg me and whatever I was carrying.
Ideally, a design should place the 10 kg mass of the engine where it doesn't change the existing center of gravity (CG) of the bike fore or aft, but that's difficult. And, as I would estimate from my experience, such a mass, fixed to the frame, should be tolerable in almost any position.
I'm considering the behind-rear-wheel position because the height of the engine in the rack-mount position on an already-tall 29" bike makes swinging my leg around to mount an acrobatic feat.

 

[Nehmo]

I managed to connect a cable directly to the lever attached to the vertical shaft coming out of the carburetor. In the opposite direction I used a spring. I bypassed the governor as Wayne z and others recommend. The other end of the cable goes to a brake lever handle on the handlebars. I started the engine and it works good enough for now.
I don't like my pivot bearing. It's too sloppy. I need so find a tighter pair (bushing and bolt).
I'm beginning to think the whole arrangement is flawed because the engine weight unnecessarily burdening the clutch. The clutch really should operate freely.

A modified idea: If the engine is fixed to the frame, then another shaft and pulleys on an axis close to the pivot would work. IOW, Engine sits high on the frame (or lower in a step-through bike) in front of the rider. Engine has pulley -belt- pulley on shaft mounted on ladder near pivot, and this shaft has another pulley -belt- pulley on roller shaft, the same as current build.
[I'll draw a diagram later.]

 

[Nehmo]

I need to make an exhaust system. It seems 3/4" copper might fit inside the existing pipe.

Another thing: As you can see from the side pic, with some small modifications, even with this same general arrangement, the entire ladder can be lower. Having the roller shaft bearings mounted on top, the same side as the engine, would still allow contact with the tire and would move the ladder and engine lower.

 

[Nehmo]

Clutch
I now have the clutch in a workable condition. The pivot for the ladder (I explained these terms earlier, but for those who didn't read that: the "ladder" is the 2 parallel pieces of tubing that hold everything; the "pivot" is the bolt & bearing where the ladder pivots on the frame of the bike) is sloppier than I would like, but it works OK for now.

I have a long extension of the ladder going forward to use as the clutch actuation leaver. I used a piece of round tubing for this. You'll see it when I post a pic.

I need to make something to "capture" the clutch lever in the disengaged position (maybe a hook). I then could pull-start while I'm still unmounted, get on, and then release the clutch lever to engage.

Kill Switch
I wanted a kill switch on the handlebars, and I placed one in series with the switch on the engine. At this point, which is just after adding the handlebar switch, the behavior is a bit difficult to explain.

Because the switches are simple SPST in series, either turned off will open the circuit. But it seems that doesn't always kill the engine. The engine continues to run sometimes. I'll figure this out later.

Throttle Control
I did configure a used brake handle-lever & cable to directly turn the throttle shaft on the engine. It works, but there's way too much friction. I'll improve this soon.

Exhaust
After removing the stock muffler, the exhaust is just open and aimed upward. I'm open to suggestions on what to do about this. I'm going to a lawnmower joint today. Maybe they have something.

Test
So, all in all, I should be ready for a trial run on the street today. I'm somewhat apprehensive because I've had dangerous events with relatively innocent electric motors, and this is an experimental use of an ill-behaved gas engine. I should live through it, though.

Another comment I must make:
Working in an equipped shop with access to a vehicle to get needed materials is vastly easier than working out of a tool bag and having only a bike for transportation. For example, a couple of days ago, I spent a few hours - I kid you not - just getting 2 common washers.

 

[wayne z]

Lookin real good there.

As far as the kill switch, do you have one terminal to the ignition wire and one to ground? The engine is killed by grounding the ignition wire when the switch is "closed". Maybe you aren't getting good continuity thru your hinge point?

As far as the lever, I built a rack mount similar to that once. I used a short piece of square tubing bolted to the end of my long square tube lever. Bolted with a nylock nut,and a flat washer between the tubings, just snug enough that I could still pivot it sideways to catch the bike frame and hold the roller off the tire.

As far as the exhaust, you might be able to use a hardware store pipe flange, re drilled to match the bolt pattern of your manifold.
Then you could use pipe elbows and mower muffler ect.

 

[Nehmo]

...
As far as the kill switch, do you have one terminal to the ignition wire and one to ground? The engine is killed by grounding the ignition wire when the switch is "closed". Maybe you aren't getting good continuity thru your hinge point?

I'm familiar with the kill switch arrangement in which the high voltage wire to the plug is grounded. Sometimes this is just a grounded springy strip of metal positioned over the plug terminal. You push it down to touch the terminal and then terminal is grounded.

But with the Predator 79cc (manual, pdf)
the switch is closed in the ON position as in a regular SPST switch. (I tested it.) Apparently, the non-grounded side of the stock switch goes to something that must be grounded in order to make spark. I connected the handlebar switch in series using 2 wires going all the way. There's no electrical connection through the pivot. My arrangement should have worked, but something is wrong.
Searching on the subject yields a post by Eli saying the switch doesn't need to be on to run; it only needs to be on to start. I couldn't find a schematic, but I can take it apart to figure it out.

As far as the lever, I built a rack mount similar to that once. I used a short piece of square tubing bolted to the end of my long square tube lever. Bolted with a nylock nut,and a flat washer between the tubings, just snug enough that I could still pivot it sideways to catch the bike frame and hold the roller off the tire.

Hold on. Let me take a pic with this laptop. It's the only camera I have now.

As far as the exhaust, you might be able to use a hardware store pipe flange, re drilled to match the bolt pattern of your manifold.
Then you could use pipe elbows and mower muffler ect.

 

[wayne z]

No, I was not talking about grounding the high voltage lead. The stock Preddy kill switch and the extra wire hanging there is connected to the low voltage side of the coil. The switch is OPEN when the engine is running. You ground it to kill the engine.
Works this way on both my Preddys and the Chinagirl engines, and many other industrial engines. Eli has mis informed you, start and run is no different, and you have missunderstood the 79cc switch.
If you use a standard mototcycle type, 1 wire kill switch in the normal way, the switch is grounded to the handlebars or the frame, and the path to the engine ground will be through the pivot unless you have a 2 wire kill switch then you can run the ground lead all the way to the engine. Trust me, I've been fooling with small engines and motorbikes since 1960

 

[Nehmo]

I tried it last night (1:00 AM this morning). It works, and now that I have had some actual experience, I can more readily see what needs to be done.

The clutch engages well enough with just the weight of the engine.

In the first pic, you can see a metal tab on the vertical bolt gong through the top tube hooking a horizontal bolt running right-to-left through the hoop handle. This is to hook the clutch in the disengaged position. I think I can improve this by changing the hooking method. I'll try simply putting a bolt horizontally right-to-left through the top tube of the frame. The sideways play in the hoop handle is enough to allow hooking and unhooking.

The other pics were taken before I made a hooking system.

The engine needs some kind of muffler. In the wee hours of my experimental run last night, my biggest concern was the cops. If one had happened by, maybe I wouldn't be here writing this now.

The gear ratio is too low. I suppose a larger roller would do. I heard hockey pucks come in 4", but I can't find them doing a search. That means I'm back to looking for roller materials.
And yes, I still haven't trimmed the roller shaft to minimum length. You can see it sticking out to the sides.
I'm using a crossways piece of wood (not visible in these pics because it's at the far rear of the ladder) as fall-over protection.