Twin Engines

Discussion in 'Performance Mods' started by 5-7HEAVEN, Sep 1, 2008.

  1. 5-7HEAVEN

    5-7HEAVEN Guest

    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?
    Last edited by a moderator: Sep 1, 2008

  2. hill climber

    hill climber Member

    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
  3. JemmaUK

    JemmaUK Guest

    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
  4. 5-7HEAVEN

    5-7HEAVEN Guest

    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.
  5. SirJakesus

    SirJakesus Guest

    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!
  6. 5-7HEAVEN

    5-7HEAVEN Guest

    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!
    Last edited by a moderator: Sep 1, 2008
  7. s_beaudry

    s_beaudry Member

    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...
  8. 5-7HEAVEN

    5-7HEAVEN Guest

    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.
    Last edited by a moderator: Sep 2, 2008
  9. s_beaudry

    s_beaudry Member

    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.
  10. 5-7HEAVEN

    5-7HEAVEN Guest

    Thanks for props, s_ beaudry.

    SirJakesus, if I use both engines at low speed like you mentioned, I might not have to pedal start!
  11. 5-7HEAVEN

    5-7HEAVEN Guest

    The engine's in the mail!

    I just contacted David Staton. This Mitsubishi engine kit will ship out today, and is engineered to bolt on in less than one hour.

    Fortunately, the bike shop I do business with knows my bike. I bought it from them three years ago and buy all my bike parts there. Last month they scratch-built my new front and rear tires, wheels, axles and bearings specifically for severe-duty use. The matching pair have HD rims and spokes, kevlar protection, the same high-performance tires and high-speed grease.

    I kinda miss the electric hub, but at times I could actually feel the bike's frame twist from the extra 100 lbs. of e-drive.
    Last edited by a moderator: Sep 2, 2008
  12. JemmaUK

    JemmaUK Guest

    good luck with it - the clutch thing I mentioned that worried me was if the clutch was stressed from the non drive side (while the engine is off or idling) through bad alignment it might hurt bearings and mechanicals and such...

    I've had an interesting day - 2 busted spokes and a coaster brake that uncoastered itself at about 30 mph with a large and distincting pinging noise. I had to wheel the bike on the front wheel - not someone I want to attempt again - I was wheezing within 50 yards just because of the problem it caused with balancing and such.

    we want to see pictures..

    Jemma xx
  13. 5-7HEAVEN

    5-7HEAVEN Guest

    Jemma, I'm banking on both clutches' complete disengagement on cue.

    Hmmm, dual engines should produce twice as much drag at idle. Maybe if both clutches are engaged, there will be less rolling resistance at speed. If the drag is substantial, I'll try lifting the drive assemblies off the tires.
  14. SirJakesus

    SirJakesus Guest

    I've been thinking about this... Why bother with the two different gearings when you could run the same large roller on both and still have twice the power?
    I know you already ordered but it would be really nasty to have those two engines howling together with a single throttle control :)
  15. hill climber

    hill climber Member

    two of the same engines with two identical rollers, THATS SICK, it would be one bad machine
  16. 5-7HEAVEN

    5-7HEAVEN Guest

    SirJakesus, that's a possibility I can experiment with, if and when I buy another 1.5" spindle. A large roller sacrifices low end, but two engines with large spindles MIGHT push harder at all speeds with 4.4 hp at top end. Granted, because of the layout all this hp would not be fully harnessed.

    However, using different-size rollers would allow one engine to produce great low end torque AND be assisted by the second engine spinning slower and producing less power. The lower-geared engine is being helped throughout its range, so the bike should be quicker since more hp is being tapped. When the lower-geared engine reaches its peak, it is no longer usable and drops back to idle speed. The second engine is now in its optimum power range and pulls the bike to maximum speed. When you have an engine with 1.5" roller, it's like starting from a stop in second gear with a manual transmission car. Throttle response is sluggish and the engine stumbles weakly, trying to reach its sweet spot. Now if you start off in the correct low gear, the car engine will reach its optimum power quickly. Shifting to the next correct gear at a higher rpm will allow the engine to regain its optimum power range much faster. This would allow the car to accelerate quicker, hopefully reaching top speed before runing out of road.

    Sounds logical?
  17. 5-7HEAVEN

    5-7HEAVEN Guest

    Besides, the rear engine with larger roller has an ADA-1 tuned exhaust pipe, which is pretty conspicuous. The front engine will have the stock exhaust. Less power but more unassuming. I just hope the new engine doesn't **** out at high rpm. The rear engine pooped out with its stock exhaust. After I installed the tuned pipe, it screamed to redline with a 1.125" spindle.
  18. SirJakesus

    SirJakesus Guest

    I understand your point on gearing them differently however I think if you're able to manage with the single engine geared high right now having two engines geared high is still going to give you a substantial kick in the pants and it'll allow you to maintain high speeds even up hills. If you hit a hill that your current system farts out on you'll have to shut that motor down and go back to the low gear engine. With two geared the same you'll have lots of power through the full range of the engines powerband. It'll definitely be a cool experiment either way. Are you thinking about mounting one large gas tank that both engines feed from at the same time or are you going to run two separate tanks?
    Last edited by a moderator: Sep 3, 2008
  19. Torques

    Torques Guest

    Will the bike be attractive with two engines on it? ha ha
  20. 5-7HEAVEN

    5-7HEAVEN Guest

    Torques, it'll be like having two large red/black overgrowths instead of one.:cool:

    Dave Staton reminded me that the bike might be off-balanced and heavy to steer. I've carried heavy batteries in my front basket for my e-motor before, so I can live with it. I hope I don't have to change my suspension fork, because it definitely softens the ride.

    SirJakesus, my plan is to charge up the hills, maybe with both engines firing. The 1.25 low roller is a good compromise and should pull strongly. If it doesn't redline, then both engines pull the bike uphill. If the front engine overrevs, I release its throttle completely and rear engine is on its own. If high gear poops out, all I do is throttle both engines to accelerate the bike upward or pedal-assist. My hills are few, short and medium-sized, unless I take the long way home. There are two steeper hills worth challenging.

    I'll use the stock tanks for now. The teardrop tank would be hard to mount, since "Girlie" doesn't have the center bar. It's an inconvenience to fill the tank every 20 miles, so now it'll be a double PITA.
    Last edited by a moderator: Sep 3, 2008