50cc to 80cc conversion...

Discussion in 'General Questions' started by Sillycodman12, Jun 14, 2016.

  1. Sillycodman12

    Sillycodman12 New Member

    Is it possible to convert a 50cc 2 stroke
    engine to an 80cc?

  2. jaguar

    jaguar Well-Known Member

    No, the stud spacing is different.
  3. JunkyardDog

    JunkyardDog Active Member

    The so called "80cc" engines are only 66cc. They are illegal almost everywhere. And cops are learning how to spot them. For me it would not be worth the fines and legal problems. My state has a 20 mph speed limit for MB, and a 48cc engine will reach that easily. My engine is 35cc, and it reaches 20 mph.
  4. jaguar

    jaguar Well-Known Member

  5. Marhsall

    Marhsall New Member

    I don't know about the weight, But there are true 80cc Honda motors out there, for dirt bikes, I'm wondering why the tranny couldn't be removed for less weight, and the engine used.
  6. JunkyardDog

    JunkyardDog Active Member

    The transmission is an integral part of the crankcase, and cannot be separated. And not only are those engines really heavy, but they have completely different mounting points than a bicycle motor. An 80cc Honda dirt bike motor would rip a bicycle frame to pieces. If you want an 80cc bike, they already exist. The Honda Trail 90 is a really cool bike, the Honda Cub based Symba 100 is also a nice bike. The Kawasaki KE100 is also a fun little bike. Or if you just have to modify something, get a moped. I have made 50cc mopeds go close to 60 mph with extensive modifications, including an 80cc top end. They didn't last that long, because the bottom end cannot be modified, and would handle the extra power

    Most motorized bicycle laws are for "motor assisted" bicycles. They were never meant to be fast. They were never intended to go faster than your average pedal bicycle. The only difference is that you don't have to pedal them. If you want speed, look elsewhere.
  7. jaguar

    jaguar Well-Known Member

    the bottom end destroyed itself because of the extra stress from the imbalance caused when you went to a larger piston.
    you should of modified the crank wheels by drilling extra balance holes in them.
  8. I keep seeing people say that about the laws. It truly depends are where you live. There are 52 States after all. I know in some as where I live you can have up to 125cc's on a bike. The only reason I haven't built one yet is, It seems very unclear even to Dmv, as to whether it needs to be insured or registered. I seem to be just about the only one in this county that has a motorized bike so that's understandable. I just don't feel like arguing with the police and the courts/ As far as what Dmv has on their site. The only requirement for anything from 50-125cc's is a license and a motorcycle endorsement. But it is legal here.
  9. Steve Best

    Steve Best Active Member

    As a foreigner I may have missed something, but I thought there were still only 50 states?

    Actually I am doing it the other way, putting a cast iron 49cc Minarelli vertical cylinder on my 66cc base.
    It is not a simple swap. A new intake and exhaust are needed, a cylinder spacer, a reed valve and some fancy drilling and grinding.
    I will have a street legal 49cc 2 stroke 6-8hp engine. Cost will be about $250 plus the $125 Chinese bottom end.

    A bit of head and port work on my Grubee 48cc engine had it working as well as the 66cc Grubee.
    Ultimately the 66cc will go faster but the 48cc is no slouch. Rips along pretty good at 30mph+ on the stock sprocket.

  10. Frankfort MB's

    Frankfort MB's Well-Known Member

    There are only 50 states:p
    A couple of territory's but they aren't states....

    I'd like to see this upgrade when you get done! Some crazy stuff if you can get it too work
  11. Steve Best

    Steve Best Active Member

    So much to do and so little time to do it.
    This is the cylinder and head in the orientation they go on the scooter.
    Scooter uses a fan to blow the air crosswise:


    I like that is says 49cc on the cylinder.
    This is how I'd be running it on my bike:

    The cylinder offset is due to tuning it 90 degrees. This is how it will bolt up. Large 1" exhaust instead of the 3/4" on the China Girl.

    Combustion chamber is fair, lots of transfer port area:

    Lots of cylinder port window area:

  12. Chevynova410

    Chevynova410 Guest

    What is the name of that cylinder and where do you get it? What about the big hole is that the intake side?
  13. zippinaround

    zippinaround Active Member

    nice found it! haha man that looks like a mean cylinder!
  14. Steve Best

    Steve Best Active Member

    This is a cast iron 49cc Minarelli vertical cylinder made for 50cc scooters. Reed valved and making about 5hp, it will almost fit on our China Girls with a little adaptation. This cylinder is absolutely stock, but there is an aftermarket for these. The Minarelli horizontal engine has a 50mm bolt pattern and would take some work to adapt.
  15. LRSimons

    LRSimons New Member

    Very cool! Is there a coating on the cylinder? I'd imagine that with a harder metal it wouldn't be as necessary. Looks to be a machined finish from the picture.

    It would be great to have a china girl made from iron/steel instead of pop cans and crappy chrome coating. It's not like it's going to weigh much either way. You've got me thinking again about machining one out of steel...

    Hope the case threads don't rip themselves out from the torque keeping that beast together!