Honda 125cc Inline 4 Cylinder Monkey Bike

Honda 125cc inline 4 cylinder Monkey Bike

Honda 125cc inline 4 cylinder Monkey BikeThe little Honda Monkey bikes, the 50cc Z series mini bikes, are pretty popular in some countries. Some fans of the little guy really engineer very nifty modifications, like this 125cc inline 4 cylinder engine for instance. It's so small it looks like a model but it's a real engine and sounds great!

Not a lot of detail on their website but very, very cool.

Thanks for the tip, Aaron!

More photos and video below:

Honda 125cc inline 4 cylinder Monkey Bike

Honda 125cc inline 4 cylinder Monkey Bike

Honda 125cc inline 4 cylinder Monkey Bike

Link: Wirthwein Motoren



  1. Mike says

    Where can I get one? This would make a VERY COOL engine to run while having beers in the garage.

  2. Rasmus says

    It isn’t running at very high rpm like other small inline fours. I wonder what it would be like with four carbs in stead of one… But still very cool. Nice engineering.

  3. matt w says

    Not so different from an Alan Millyard creation but I think he’d have used four carbs. It makes great noise but doesn’t seem to have the oomph! Four carbs = at least a couple hp. Maybe next time they can make a 200cc four and stick it in a CT70 or ST90!

  4. skeeter says

    Why don’t the big manufactures build street-legal fun punky little bikes? The Honda Ruckus comes close but it needs a 100cc engine rather than 49cc (a safety issue with the hills). If this 125cc 4-cylinder bike were street-legal and available in the USA I would buy it in a second as my city scooter.

  5. guitargeek says

    Honda does make the 250cc Big Ruckus. I hear they’ll do about 75mph on the highway, but I’d still rather have a proper motorcycle.

    This little monkey bike is a great example of brilliant engineering!

  6. WRXr says

    Forget about four carbs.

    It would be cool if they could adopt the new Honda Cub 50cc FUEL INJECTION for this. One injector per cylinder.

  7. Wolter says

    I have my doubts. If you look at the head, I can’t see any way of driving all thoses tiny whiny values?

  8. Mikey says

    Loomis, the cam is run off of a drive belt behind #2 cylinder. There’s a drive “box” back there.
    The timing belt looks like a very small toothed drive belt, looks a lot like the drive belts in copiers and medical equipment.
    The single cam has a matching drive pulley dead center.
    Check the Wirthwein webpage for closeups.

  9. QrazyQat says

    Why don’t the big manufactures build street-legal fun punky little bikes?

    They do. In Thailand and elsewhere in SE Asia. The question is why don’t they import them to North America?

    How about doubling up this motor for a 250cc V-8? And twin four-barrel carbs.

  10. Murray says

    Honda competed for the 125 world championship in the ’60s with a FIVE cylinder 125. With five carbs. With four valves per cylinder. But it was built by a factory team and probably worth the equivalent of a quarter million dollars in today money. This is brilliantly done.

  11. Murray says

    Nice to see the Stig fully wrapped for his test ride, too, rather than the usual kid in flip-flops who grins fit to bust until he decks it….

  12. atombomb says

    Does anyone know what the website is for this engine i tried searching for it but to no prevail. Any info would be nice.

  13. seb says

    very great sound
    pour les francais c’est trop de la frappe respect pour ton ingéniosité

  14. Ductapecrzyglu says

    I see that it turns left and right, But does it wheelie? I think this would be the coolest pit bike at the track.

  15. Dave Temple says

    Brilliant :)

    What a fantastic howl from that little engine……excellent piece of engineering, i think i,m gonna use the sound as a ringtone on my mobile lol.

  16. thewindmillman says

    what a sound …..lovely job…… sweet job i think every one should have one of these thanks for putting this video up


  17. says

    I have a 2008 gio125cc motor put into my 1983 Honda z50 bolts right in and goes way faster than that inline 4 he has there. Wheelie any gear anywhere in the rpms. Recently purchased a 1974 Z50 and it is also getting a gio125 motor (actually purchased already)