Introduction: The Stealth Bike

About: I love to make things and challenge my mind! I started playing with Lego's when I was 2 and it led my to peruse engineering throughout school.

Where I live mounting an engine to a bike makes it a moped if it's under 50cc, which I would need a license for, and if it's above 50cc then it’s considered a motorcycle which I would then need a motorcycle licence for. So, either way I need a licence, and I am too young for that. I decided I needed to disguise my engine so if an officer drives by, I can kill my engine and pedal the bike, making it look like an ordinary bike with a crate on the back.

Your probably wondering why am I making this? I'm making it because I live in the foothills and theirs a lot of hills, so I wanted a way to go up hills with less effort and cruse around my neighborhood. I have always wanted something I can ride around and scene a car is a couple years out, this is a great replacement. Please enjoy :)

Step 1: Parts and Tools You'll Need

The 79cc Predator engine from Harbor Freight - $110

420 Chain, on Amazon - $14

You can make the throttle or you can order one, I decided to make one using my family's 3D printer and parts from another bike.

Sprocket and pineapple bushing I got on amazon that has both parts - $20

For a throttle return I made one with a spring (from the engine) and with a scrap piece of right angle aluminium.

You're going to need gas and oil, gas price varies on where you live but get 87 unleaded. The oil you'll need is 10w 30 it was about $4.

I got a centrifugal clutch that is sold for $25.

You’ll need a chain breaker which you can get at harbor freight for $14.

I didn't have a kickstand and I needed one so I got one for $10.

You'll want to get a tachometer so that you can monitor your engines RPM, I found one for $15.

You'll need 2 pieces of right angle steel that's 1X72 inches - $13. You’ll need 1 inch square tubing - 16 and a 72 inch piece of flat stock - $10.

Now that you know the parts you’ll need, we’ll need to talk about tools. I needed a welder so I got the welder from Harbor Freight. I got the 90 Amp one and an auto darkening mask (you will need this). I also picked up the bundle that had a leather welding apron and leather gloves (you will need this). If you want to you can also pick up the Flux Core welding wire .030" NR - 211, because the stuff it comes with is junk (you don't need this). Also at Harbor Freight you're going to want to get a welding table (doesn't require it), and a 6" cut off wheel (doesn't require it) because we are going to do a lot of cutting. The table is $75 and the cut off wheel is $45, plus additional cut off wheels. You're going to need a angle grinder with a cut off wheel, a grinding disk and a steel wire disk (required). Finally you’ll need a drill with big metal bits up to 3/8th inch (Required).

Step 2: Throttle Return and Linkage

Now that you have everything that’s needed, watch the video above because it's very hard to explain what you need to make so follow what I say in the video and repeat it.

You'll want to start with taking off the gas tank on the engine. Remove the nut that holds the current adjustable throttle in place. Save that spring for later. You'll want to drill small holes in a piece of right angle Aluminium that corresponds with the ones on the governor. Then one on the other side of the angled aluminum piece to hold the spring in place and another one for the throttle cable that you can get from another bike. Take some small bolts and nuts to secure the L piece and governor against each other. Now you'll want to reattach the gas tank. Make sure that when you tighten down the nut above the drive shaft that you bend and pinch the spring in between the gas tank and nut because that is your throttle return. Later in my Instructables, you'll notice that my exhaust is completely different then what you have. Originally I planed on putting my engine between my legs, so I cut up the exhaust and so that's why I had to make one. You don't have to worry about this you can leave the engine's exhaust as is.

Step 3: Twist Throttle

Okay, now that your engine has all the modifications that it’ll need, let's work on the other side of the throttle. It was easy for me to make one, but buying one assembled might be easier if you don't have the resources (3D printer)

Use a sharp knife or box cutter, to remove or cut off the current grip on the handle bar. Once you have it off, assemble the throttle by taking the piece with the tube coming out of it and orient it on the handle bar and mark where you need to drill the hole. Then you can assemble it from there. Take the actual twist throttle and slide it on the handle bar, then take the bottom piece and hold it on the bottom till you can put a bolt through it. Take the other side of the brake cable or throttle cable and put the nub in the handle. After that take the top piece and set it on top, line it up and put the screws threw it and tighten them down. Take a piece that would hold the black cable from another bike usually found in the brake handle, and thread it into the tube coming out of the bottom piece. From there you can wire the cable to the engine and find what works best. Then you need to tighten down everything and if you want you can wrap the handle in tape to give it padding and grip.

Step 4: Sprocket and Pineapple Bushing

Now you want to remove the back wheel and on the side that doesn’t have any gears is where you'll want to mount the sprocket and pineapple bushings. I’m not going to describe this fully because there are a bunch of videos and tutorials on how to install it. Basically you want to cut one side of one of the rubber rings and slide it under the spokes. Now you want to line up the three metal plates with the holes on the bottom. Set the other gasket on top and then the sprocket. Next place the nine bolts through all the holes. On the other side put a washer, and a split washer then tighten them all down so the sprocket is flat and in the middle of the wheel hub.

Step 5: The Engine Mount

In the picture of the black frame, ignore the four black pieces coming off. Those will be welded on in the next step.

For this part you're going to start making your engine mount. Start with cutting two pieces of angle steel that are 9 inches long. You're also going to want to cut a 4 ¼ inch piece of square steel tubing. Lay out one of the angle pieces and lay the other piece so they're a mirror of each other. Then lay the piece of square tubing in the middle of the right angle steel and pinch it together. Now weld all of the pieces together.

Step 6: Finishing the Engine Mount

You now want to cut four, 7 inch pieces of right angle steel. Lay the mounting plate downside. Then you want to butt weld the pieces together, so you get a smooth top. Mirror this on the other side of the engine mount. Then you want to repeat it on the front but leave yourself an inch because you need to drill a hole later.

Step 7: Engine Bracket

This is where you’re going to want to cut a 15 inch piece of flat stock and a 5 inch piece of angle steel. Mark the flat stock at 5 and 10 inches so you have the piece in thirds. Now clamp down the piece vertically in a vice and heat up the area around one of the marks and bend the flat stock. I used a big pipe as a breaker bar, but you can do whatever works for you. Then you want to flip it over and repeat the process. Now clamp the angle steel and the bent bar together and drill one hole in the middle and one on each side. When you assemble it you want to place the angle steel behind the bar holding your back wheel and clamp it all together. Then you want to bend the side of the c-bracket so it’s parallel with the left of the wheel when your looking at it from behind. Now set the engine mount with the 4 pieces welded on and set the front of it on the piece you just attached. You want to drill through both sides and repeat on the other side.

Step 8: Engine Mounting Frame Part 1

Here you want to cut out 2, 4 inch pieces of right angle steel and clamp one on the bottom bar that holds the back wheel and one just above it. Make sure you slide them over toward the back wheel bars. Then lay a strip of flat stock that’s about 5 inches across the both of them and weld them so they're one piece. Now depending on your bike you're going to want to attach it to the frame. I added tabs to my mount and screwed it into a hole on my bike frame, then I used hose clamps to attach the tops of the bracket to the frame. Then repeat this on the other side. It’s important to note that the hose clamps are just keeping the frame from slipping off the bike, the right angle is taking the weight.

Step 9: Engine Mounting Frame Part 2

You want to cut two pieces of angle steel that are 7 inches long. You will want to weld the pieces on to the brackets you just made. Make sure they're flat and parallel to the ground and go straight back. You will want to tighten down the engine mount with the front nuts then make it level. Add a vertical bar that goes straight up from the bottom horizontal supports to the back 7 inch angled steel bars coming off of the engine mount. Drill a hole between the overlap, add a bolt and tighten it down. Repeat on the other side.

Step 10: Attaching the Clutch

Slide your clutch on so the gear is right next to the crank case. Use a 5/16th 24 nut to hold on the clutch. On the other side of the engine take of the pull starter case and hold the big nut still while you tighten down the nut that will keep the clutch from falling off. We need to do this to hold the crank shaft still to get the nut tightened down. Now before you line up the engine we need to make a simple part for the chain breaker. Cut a slot in a scrap piece of flat stock that will then slide it over the axle that's used to push out the pin, which keep the chain from breaking.

Step 11: Mounting the Engine

Now lean your engine forward so it’s resting vertically and you can get under it. Add the engine mounting plate that it came with. Flip the plate around so when we add the clutch its as far over to the right as it can be and line up with the sprocket. Set the engine on the now firmly supported bracket and line it up so it's straight and goes down to the sprocket that you added. Mark where you need to drill the holes take off the engine and drill the holes. Make sure that when you bolt the engine you use strong bolts. I got grade 8 bolts. When you attach the clutch and then the chain, you may need to add spacers underneath the engine to raise it, I added a combination of pieces of aluminium and drilled the same holes, then stacked on some nuts. You want to tension the chain so that it won't come off. The chain when finished should have an inch of deflection.

Step 12: Wiring Everything Up

You're going to want to print out or make a bracket that can hold the Tachometer. I mounted it under the steering shaft and wired it up. For the throttle you'll want to weld on a nut that allows the wire to run through and stops the black plastic tubing that protects the wire. On the engine mount I cut a piece of flat stock that was 4 inches and drilled a hole so I could bolt it onto the engine. Then you want to cut a inch piece of angle steel and drill a hole that will hold the wire stop and weld it onto the flat stock. I then tightened down the wire stop and finished hooking it up.

Step 13: Making the Box

Okay, to disguise the bike engine I made a box that sits on the posts we welded onto the engine bracket. Get 4 pieces of 1x2 inch, and a bundle of wood lath. I made a box by cutting 4 pieces of 24 inch, 4 pieces of 18" and 4 pieces of 13". I made it into a box, and here is the layout for it. Then I made a lid that sits on top of my box, and covered all the edges with thin thatch wood. I added wood that lies flat on the inside so that the box can rest on the bars, then I drilled holes and attached it. If your cables and pull start are an issue you can make a rectangle cut out in the front and make openings, which is what I had to do.

Step 14: Conclusion

Now you can line up the box, drill some holes and mount it. Thank you for reading my Instructables. I had a blast making it and through all the challenges it was a huge success and I look forward to riding around in my neighborhood and I hope you do too if you make one :) The cost for me, was $388, but if you pinch pennies and have all the tools and use free salvaged parts it should cost you $170 (or less with a harbor freight coupon)! The finished bike goes about 25 mph on flat land (without pedaling) and if i'm going up hills I can still pedal.

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