Twin Engines



Anyone try two engines on one bike?

I have a Raleigh women's cruiser bike on steroids that I call "Girlie". She's had a 72-volt electric motor but now runs a Mitsubishi 2.2hp engine with tuned pipe, friction drive and 1.5" roller. I had a 1.125" spindle on it, but the engine redlined at 20-something mph. Acceleration was good, but it overrevved if I tried to keep up with traffic. I wanted more speed, so I installed a larger-diameter spindle.

Since replacing the roller, I can live with the soft low end because I now ride safely with the flow of traffic. I also like the top end, but I need more acceleration. Also, hillclimbing needs improvement because of the 1.5" spindle. I COULD reduce to a 1.375" roller, but the thought of running engines front and rear fascinates me!

Here's my idea: One solution would be to install a second engine, like a Staton front-mounted friction kit designed for trikes. To simplify matters, I'd use another 2.2hp Mitsubishi engine and a 1.125" roller. This would give enough low and midrange power to scream to 25mph. At that speed, I release its throttle back to idle and floor the rear engine, which had been idling all along. With the 1.5" spindle, the rear engine takes over for high end duties while the front engine idles. If the engines are identical, it'd almost be like shifting gears.

Do you think it'd work?

Has anyone done it?
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put the 72 volt motor back on it as a hybrid and use the electric as a kicker. i got a ht mountain bike that i have been depating putting my 43cc friction on also with the ht as a kicker for the hills
firstly you might find problems with fried clutches...

secondly you would have more controls than you knew what to do with or could operate safely

Thirdly - there is a very good chance thats completely illegal. I know it is in the UK for a fact. You cannot drive/ride/operate *anything* on the UK roads that has more than one engine/transmission pairing.

Hybrids get around this by simply calling the hybrid units a single propulsion system, strictly they are illegal by the letter of the UK law.

What might work is a dual roller system. the first position would be for speeding up and then the assembly is further dropped down to engage the fast road roller - its a much simpler variation of the multi ratio belt and adjustable sheave as used on early bikes such as the rudge machines. It could be done by spring-pinioning the roller assembly against the motor mount so that in the first position the engine/roller is locked to the tyre and then when you want to change up the pinion is dropped down to the higher ratio. The trick with that setup is getting the spring rates and tensions right so its easy to vary the ratio

Jemma xx
I thought about reinstalling the electric hub, but the memory of carrying and recharging 80 lbs of batteries turns me off. Since I live in a walkup, it was too much trouble to R&R the heavy batteries.

I have no idea why the clutches would disintegrate. Can you explain? At idle, the engines disengage their clutches. If needed for less drag, the friction drive assemblies can be modified to disengage and re-engage via cable control and doorsprings.

Right now, I have a brake lever and a thumb throttle on the handlebars. I can handle another thumb lever on the left side.

I'm not concerned about legalities, and local police aren't either. I've never gotten a second look from them. The cops MIGHT take notice if I had a frame-mounted engine, since it resembles a motorcycle.
Sounds simple enough to do and thats way less controls than a motorcycle. I'd say go for it. The baby will HOWL right in the middle when you're running both engines at the same time though... and don't say you wont because I know I would!
Pedal 3-5 strokes, hit low gear engine speed up to around 15mph and then engage high gear engine all the way up to 25 or so when the low peaks out and is dropped to idle.
Sounds fun as heck!
SirJake, after a few practice sessions it'll be more like:

1. Start and idle both engines.

2. Pedal from a dead stop.

3. Throttle the front engine to redline rpm.

4. Release throttle; when front engine speed drops to idle and its clutch releases, throttle the rear engine to desired speed.

The engines' speeds might sound like a slow shift change. Low speed and midrange should be awesome. Top speed might be faster because of the acceleration.

SirJake, if I throttle both engines simultaneously, the front engine would redline at 20-something mph. Then the rear engine will force the front one to its death before reaching 40 mph.

You're right; it sounds like great fun!
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I like the idea of two engines...

But there has to be a way to use only one and cover what you are looking for in terms of speed and torque...
S. Beaudry, Jemma recommended a multi-ratio roller system which is completely beyond my capabilities. And if I sell my bike and get a multi-speed bike, I could install a chain drive system and try to imitate what others have done for a twin-sprocket gear ratio. Or a new bike with NuVinci hub.

Although using two friction drives is the simplest way to double engine capacity on a cruiser bike, it is not cheap.

However, it is the cheapest way to double engine capacity or experiment with the aforementioned.

And of course, a front disc brake might be in the works. If my Rockshox fork doesn't clear, it's back to the original fork or a single-post suspension fork.

Let's not mention street legalities anymore. The bike is registered for as long as I own it. There are thousands of mopeds here that police are monitoring for noise, speed, modifications. stolen property. I have never seen another motorized bicycle here. I am invisible as long as I ride in a sensible manner.

If I don't hide one engine, I won't be invisible for long.

If the project fails, I can retrofit the extra friction drive onto my wife's cruiser bike.
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It is well worth the try.... I have learned way more by failing then succeeding myself!

Just keep yourself safe, remember the added weight to the front and back end and different center of gravity while stopping or turning may throw you off a little bit.
Thanks for props, s_ beaudry.

SirJakesus, if I use both engines at low speed like you mentioned, I might not have to pedal start!