Solenoid V-Twin Harley Davidson Motor

After making a solenoid motor in a couple of afternoons in the workshop I thought I should go for something rather more sophisticated. I wondered what a Solenoid V-Twin Harley Davidson motor would be like? One of the first objectives was to measure and improve the force developed by the solenoid. This would then allow me to operate the solenoid on the basis of a 4-stroke engine.


I made the bobbins for the solenoids from bog-oak. You can see in the later images that I drilled small holes in the ends of the bobbins to thread each end of the wire through. The bobbins were wound on the lathe at a low speed. BE VERY CAREFUL DOING THIS.

The armatures were machined from mild steel and then drilled.

Gears and Timing

I constructed this as a 45° V-Twin with a 4-stroke action on the solenoids, hence the 2:1 gearing on the operation of the switches. I cut the gears (see also: Gear Design) using a combination of Hobbymat MD65 lathe and Unimat 3 milling machine.

The frame of the engine was made from a homemade plywood, giving a lovely contrast in wood colours along the edge of the frame.

Brass Gears
two off brass gears for the cam drive

Each cylinder fits to one of these plywood frames and the crank boss goes through the 2 frames at the bottom. This allowed me to stagger the frames and so give the necessary offset for each cylinder centre, required to achieve a single pin big end. This gives the distinctive v-twin arrangement of a Harley-Davidson.

From the rear of the engine you can see the single pin.

When the crank is nearly at bottom dead centre both pistons for the solenoids are out of the bottom of the coils.


I made the crankshaft as three separate pieces. First the main shaft was machined from mild steel and the crank machined from brass that was then soldered to the main crank. The crank pin was then soldered to the crank. There is actually a fourth part and that was the timing gear that was machined seperately and once again soldered to the crank. In reality I held all of the pieces in a jig and then heated the crank, once hot I then touched some solder onto each joint.


I machined the conrods together as a pair from aluminium. With small ball-bearings in the big ends and plain bearings in the small ends. Once the conrods were machined and slotted I then bent the sides. I achieved this using 2 inch half round pieces in the vice to form the curves.

Pushrods and Switches

I made the pushrods with brass pads on the ends to run on the steel cams. I only made plain bearings for the cams with a light oil lubrication. The pushrods run in brass tubes, I decided to lubricate these with graphite. The pushrods operate small micro-switches.

The wires have shrink wrap insulation on the ends. I applied the shrink wrap in two stages. Firstly, a short piece that was shrunk with the soldering iron and then over the top of this a longer piece of shrink wrap. The effect is rather nice.

In the foreground is the boat shaped frame, this was designed to represent the lower part of a bike frame.


I machined the flywheel from a solid piece of cast iron. I machined the slots on the rotary table. The only small design problem was that I machined the end of the crank 6mm in diameter. This meant I had to centre drill and tap a 3mm thread. This ended up as a rather limited face to bolt the flywheel to.

The idea behind the 45° V-Twin with a 4-stroke action was to create a Harley-Davidson like sound from a solenoid motor.

You can judge how close I got to this target by watching the youtube video of the engine running and listening to the sound. Is this Solenoid V-Twin Harley Davidson Motor sounding like a Harley?

I made the video when the engine was at an early build stage, hence the engine being mounted in a rough working frame. I use this type of frame a lot as it allows me to work on the engine in the workshop and not worry if I damage it.

The power to the engine was provided using 4mm banana plugs and a good 12V 2.5A power supply to run well.

I must update the plastic covered brown and blue cables with some cloth covered ones as they will add to the look. This motor is all about looks…

single piston solenoid motor plan

The single piston solenoid motor is available as a set of downloaded plans. These plans give you the basics of a simple engine design from which to then use your imagination for more complex motors.

More of my engines are in my gallery page.

4 thoughts on “Solenoid V-Twin Harley Davidson Motor”

  1. Hi Nigel,
    Nice job , but if the V is 90 , it will be better so that there will be always rotation when the power is on.
    Best regards, Ata

  2. Fun project. It has some of the off-beat quality of a tiny Harley 🙂 The motor seemed to drag /slow every x no of turns. I notice the crank is evenly weighted & wonder if a bob weight would smooth it out? I’ve never looked inside a Harley but most bike cranks are bob-weighted in some way to smooth & balance out undesirable frequencies. Addition of some plasticine might prove it with your “motor”

    • Hi Rob,

      The single pin and fact that the two cylinders are in a 45° V and designed to fire one after the other means you get two power strokes 45° apart and then 720-45° of rotation before the next power stroke. Agree on the counterweight, not sure what was going through my head at the time.

      I have thought of re-making with laminated iron core cylinders and getting rid of the “four-stroke” that limits the number of excitations of the coils.

      Best regards, Nigel


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