An Airboat and a Bike Had a Baby and it’s Rad

Bikes Drones & Vehicles Workshop
The Screaming Rabbit
The Screaming Rabbit
Photos: Jared Birkholz

While doing some research on custom bikes I came across the amazing Rat Rod site and their lively community. One custom bike in particular, the Screaming Rabbit, caught my eye as a unique project worthy of highlighting on Make:. The bike uses an airboat motor for some extra propulsion and delivers a sound that must be the bane of the neighborhood.

I got in contact with the bike’s creator, George Davis, who created the Screaming Rabbit as part of a Rat Rod build-off competition. He had this to say about the bike’s inspiration.

“It started out as an idea I got after seeing an airboat motor in action and then when I suggested the idea to a couple people I was told by all of them that it wouldn’t work and couldn’t be done. That was all it took for me to try. Three months of tinkering in my basement after my son went to bed, and mission accomplished.”

Airboat Power

The Screaming Rabbit

In addition, Davis created a detailed build diary documenting his time creating the Screaming Rabbit. You can read the full account and comments on Rat Rod’s forum. With Davis’ permission, I’ve included a condensed version here.

Animated Screaming Rabbit

Screaming Rabbit Air Bike Build Diary

May 1, 2015
I have been wanting to build a motorized bike for a while so here we go.

My last build for the MBBO was powder coated and looked like it came straight off the floor at K-mart. This time I am going the opposite direction and keeping it crusty. Since I don’t know anything about motorized bikes, I will be breaking all the rules and doing it my way. I will admit up front that my “big idea” might not be entirely possible, but I will be putting it to the test.

As for the name, I am undecided between the Dragonfly-er or the Screaming Rabbit. I think it will become obvious why either name will work as I get into the drivetrain. Here is a taste.

Bike Frame

Airboat Motor

May 4th, 2015

First things first, I need to get a roller together. In the plan I had in my head I thought I would piece together the original fork with the business end of a Monark springer that I picked up a while back. I had to do some flipping around but I was able to get it to work the way I had envisioned, but… without the other half of the Monark I have to balance limiting the action with making sure it doesn’t fall apart. It looks good but it makes me a little nervous, especially on a motorized build.

Frame Work

I have a couple other springers to choose from but I am not sure about them either. Next option is this standard Schwinn knock-off. Not only does it look kind of ordinary, I think it is off an Electra and it is the kind where the braces are welded to the fork just above the dropouts. At least with this one I wouldn’t have to worry about it holding together.

Frame work

Third up is the old Rat Trap. I don’t see a lot of these used on motorized bikes, which makes me think there is probably a reason.

Frame work

Any input is appreciated, but may also be ignored.

May 11th, 2015

Things are slow moving over here and with a week-long visit to the in-laws on the horizon, it might be a while before I can get it motorized. I was able to remove all the decals from the frame and do a little Dremel work in order to get the rat trap to accept a bigger axle.

At least now I have a roller and will be able to figure out a level motor mount.

White Tires
May 14th, 2015
I am heading out of town to the in-laws for a week so I have decided to wait on mounting the motor until I get back. In the mean time I found a slightly mangled Sears / Raleigh knock-off at a police auction that I was able to pick up for 5 bucks. I really just wanted the pedals but I am cleaning up the grips too just in case. Unfortunately the pedal adapters are going to cost me triple what I paid for the bike but the pedals match the tires so well I feel compelled to use them.

White Pedals

White Tires

I also mocked up these Elgin guards I picked up with a PeeWee replica in mind. Doesn’t look like I am getting to that anytime soon so they are being considered for this build. IF, IF, IF I use them then I have to figure out whether to paint and patina them to match the rusty chrome fender, or to do the fender as well.

May 15th, 2015

The slow trickle of parts keeps rolling in. Whenever I order parts I am unfamiliar with, it is always a bit of a gamble.

Will it be as described? Is it a quality part? Will it work for my bike?

Center Standoff

This time I feel like I hit the Jackpot! I snagged this 1960’s era Swedish-made TRYGG center stand off of Evil-Bay and I couldn’t be happier with it. The seller said it was removed from a 26″ Raleigh but I had no idea if it would fit on the Worksman with balloon tires. Turns out it fits perfectly. So perfectly that not only does the bike stand straight up but it does so with both tires firmly on the ground. On top of that this thing is really beefy. All of which will be crucial as this build progresses.

Night Bike

The fact that the base hangs down 5 inches under the BB is some added character that I didn’t originally envision but I can live with it. Overall I am very pleased and I will be keeping my eye out for more of these.

June 9th, 2015

I have been off the radar for the last couple of weeks and while no actual work has been getting done, I have been working hard on the build I have going on in my mind. I have also been collecting parts and have picked up a few important pieces and have finally settled on a name. This bike is officially called the Screaming Rabbit. Here is a preview of the badge Xavier (aka AXSEPUL) did for me.

June 21st, 2015

I got some work done on the rear rack this weekend. Started with a 5 inch piece of channel aluminum and started cutting away. Still have to clean up some rough edges and drill a few holes but I feel like I am making a little progress. For braces I will be using the struts off a 20 inch springer.


Fathers Day Strut Cut

Strut on Bike

June 26th, 2015

Slowly chipping away at it. When I tried to put the chain on today I discovered that the sprocket I have mounted up is a little wonky so I will be breaking it down and swapping it out. The rack looks like it is going to work well but I am still ironing out the mount. I also hope to have the motor mounted up soon but in the meantime I have been trying to figure out the throttle and kill switch set up. Lots of trial and error but I think I’ve almost got it sorted out. In the meantime here are photos of the bike with the front fender mounted up and also the bars/throttle I will be using. Its a thumber off an old Honda Big Red three wheeler.

Screaming Rabbit Bike Progress

Bike Throttle

June 29th, 2015

Sprocket swap has been completed and the rack is mounted. I also got my long spring Messenger set up. If the seat post clamp seems a little high that is cause it is. The seat post was REALLY stuck. I have been alternating between Aero-Kroil and PB nearly every day since the BO began. I have also tried heat and had no luck with that either. Finally I realized that the old school seat post already clamped to the seat was a perfect fit to slide right into the Worksman post. All I had to do was cut a couple slices down the old tube and slap a clamp around it.

Night bike with Seat

June 29th, 2015

Here it is with the seat off and the clamp slid down a bit. I put two slits (one cut) in the seat post about 3/4 of an inch down. I had to add a spacer so the clamp would fit and I put a slit in it all the way through. Works great and if somebody 7 feet tall wanted to ride it I could probably raise the seat high enough. Any shorter than where it is at now and I would have to take some off the stuck post.

Seat post

July 10th, 2015

Time is starting to feel crunchy around here. I have a lot going on the next several weekends so I will be trying to get finished up before the deadline, hopefully. I got some paint on the rear rack and mounted it up. The rack also doubles as a motor mount so I figured I would try bolting the motor in place. The motor itself is B&S 5 horse but the cage and prop are off a Dragonfly air drive boat motor. One of my big worries was that the motor would be too heavy behind the rear axle and would cause unwanted wheelies. Not really a problem but I was prepared to fill the bars with bbs.

Mounted Motor

July 13th, 2015

I am hoping my small engine buddy can make it over tomorrow night to see what else I am still missing and see if maybe we can get it running. In the meantime I will be working on the patina and adding on a few tidbits. Up first is this self contained Campbell’s light I picked up from the FS section of this forum about two years ago. It has been waiting for the right bike and I think this might be it, although I might swap it out if I can find or put together a big oversized tractor light. I also slapped on my sweet Screaming Rabbit head badge.

Can and Badge

July 15th, 2015

My buddy who knows a few things about motors came over and helped steer me straight on a few things. We got the top end of the throttle sorted out but I have to get a different clip to hold the bottom end in place. I still have the kill switch to deal with and that is the part I am least sure about. Buddy says I can hook the switch directly up to the plug just as long as I have it grounded. Sounded legit at the time but now I am not so sure. I am on my own figuring it out as he was running behind and I had to head out last night myself for a little racing.

July 18th, 2015

Still haven’t started the motor, but I feel like I am getting close. In the meantime I threw this plate down over the kickstand.

Plate on kickstand

July 21st, 2015

Plugging away here. I have the kill switch and the throttle figured out (I think), just need to get the right bend in the end of throttle cable and then it will be time to fire it up and see if she will hold together. If it works as I am hoping, all that is left is to give some of the parts a little age. In the meantime here are a few do-dads I picked up. First up is an early brass fire extinguisher I found in my grandma’s basement, cause you know “safety first.” A few spot welds on a pair of clamps and I am all set.

Vintage Fire Extinguisher

Attached Extinguisher

Then yesterday I went to the EAA Fly-In and I picked this up. Should fit right in with this build.

Emergency tab

Remove before flight

July 28th, 2015

I have everything hooked up but I am still having a little trouble with the throttle cable. I am hoping to get it sorted out on Thursday as I have the day off, but that doesn’t leave me a lot of time if there are any problems. I have decided that I am going to take some pictures FIRST and then try to fire it up just in case there is a problem. I am confident that everything will go as planned with the possible exception of the connection points for the rack. That is definitely the weakest link. Worst case scenario the connection points don’t hold and the whole motor comes shaking off the bike. Needless to say I will have my itchy finger on the kill switch when I try to start it for the first time.

Either way I will video the initial start up, and if it goes well the inaugural ride.

July 30th, 2015

The weather cooperated last night and with the help of a friend I was able to get some good pictures. One thing is for sure, this bike gets A LOT of attention and I was not the only one taking pictures of it.

Now that posterity has been taken care of I feel like I can fire it up assuming I can get the throttle to respond the way I would like first. I will post more pics in the Finished Bikes thread but until then here is a little teaser….

The Screaming Rabbit

July 30th, 2015

Engine test went well but it turns out the throttle is not ideal. It lacks the range of motion needed to make this Rabbit Scream so it is effectively running at 1/8 -1/4 power when at full throttle. An easy future fix with a different throttle, but it has plenty of power the way it is now. This video of the engine test ends with us laying off the throttle because the two of us could no longer hold the bike back.

YouTube player

July 31st, 2015

This clip is for all the nay sayers (and there have been a lot). I’ve built a lot of dumb stuff before, but nothing that has had so many people convinced it would not work.

I will be posting final pics in the Finished thread tomorrow, cause I like to drag things out.

YouTube player

August 9th, 2015

Here is a little more video for you. Before you watch it I must preface, I am not a videographer, nor is my wife a cameraman. This is just some cellphone footage she took on our ride this morning.

YouTube player

7 thoughts on “An Airboat and a Bike Had a Baby and it’s Rad

  1. Antron Argaiv says:

    Loud enough to wake the dead? Nice job!
    (does it need to be registered?)

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  2. Scott Tuttle says:

    seems to go downhill great!

    1. Ghostboy36 says:

      There’s a hipster riding it, so you know it wasn’t built to actually be practicle.

  3. Brucinator says:

    I love it – how fast does it go?

  4. William Cartwright says:

    I would like to see it go up a hill…dumbest idea ever

  5. Ryan___Disqus says:

    At least the wind will always be at your back.

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I make stuff, play music, and sometimes make stuff that plays music. Fan of donuts, Arduino, BEAM robotics, skateboarding, Buckminster Fuller, and blinking lights.

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