50cc to 80cc conversion...

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.
 
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.
 
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.
 
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.
 
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.
 
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.

Steve
 
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.

Steve
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
 
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