The Jura Big Fifty build, evolution, repair and a-ha moments

Jul 2, 2018
A final a-ha moment, courtesy of the State of Ohio:

A moped, or motorized bicycle, is any vehicle with two tandem wheels or one front and two rear wheels that is capable of being pedaled and equipped with a helper motor.

The helper motor may not:
Have a piston displacement of more than 50 cubic centimeters
Produce more than one brake horsepower
Propel the vehicle at a speed greater than 20 mph on a level surface
If a vehicle exceeds the above criteria, or any of the other specifications outlined in Ohio Administrative Code Chapter 4501-23, it is legally a motorcycle.

Operators must obtain and display a rear license plate. Refer to Digest of Motor Vehicle Laws for driver license requirements.

I remember mopeds were a lot faster than 20 mph back in 1980, but whatever. In order to be a "legal" motorcycle, I'd have to apply for a Specially Constructed title, which means dragging it to the Highway Patrol inspection station with all the receipts, then taking a rider safety course and applying for an MC license, then registering it as a MC, which includes getting an E-Check for emissions. I don't know how the hell they'd E-Check it and can't be bothered to find out. This ain't a Hayabusa, it's a moped, and now plated as such.

So forget anything I said about going more than 20 mph. Never happened, okay?


Active Member
May 13, 2010
The law here in MN is the same except says 2 hp, just thank god you are not in Washinton or Oregon 35cc max. but they pull a bike perty well also...........Curt


Motorized Bicycle Vendor
Apr 18, 2010
It's 48cc here is AZ and every build I do, except electrics of course, say 48cc on my stickers.


The PoPo don't mess with us unless we are riding like idiots like so many kids do.
The min age here is 16 and I think that is good thing, old enough to know something about the rules of the road.

I have no legal requirements for what I wear riding, but I wear a helmet, good shoes, and glasses when I ride.
I have refused people that want to take a test ride wearing flip-flops or sandals, I provide suitable footwear for a test ride if I have it so as not to loose a sale, but you have to worry about people like that.
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Jul 2, 2018
That's a nice-lookin' bike, KC!

Went for a ride in the park yesterday, thought I'd give it a good long run. Gave it 11 miles and a thorough inspection once I got home. Nothing broke, came out of adjustment, or quit working. That was a pleasant surprise, and gives me some confidence in this thing.
Apr 9, 2018
So I said howdy, now's when I share the good stuff (and the bad stuff too).

In 2016 I built the Jura Big Fifty, using an Electra Cruiser 1 and a Bikeberry 49cc 4-stroke kit. This is what it looked like right out of the barn:
View attachment 82621

And of course there were problems. First I couldn't get the coaster brake to work. Felt like it was slipping. So in spite of it being brand new, I rebuilt and adjusted it. Got real good at rebuilding and adjusting coaster brakes. Still no go. Then I decided that the coaster just wasn't up to the task of stopping 300 pounds of bike and rider, even with the Sturmey front drum helping out, and ditched it. Got a new rear hub from Bikeberry/BBR that uses a thread-on sprocket and comes with a thread-on band brake.

The sprocket and hub was a wonderful upgrade. The Bandbrake was worthless. Worse than the broken coaster brake. Then the transmission input shaft broke and I had to pedal home. That's when I had the first a-ha moment. I had slip in the pedals while pedaling forward, too! Turns out the problem wasn't in the coaster brake, but in the wide crankset. The sprocket is pressed onto the shaft, and none too tightly. Hit it with the welder (just a couple tacks) and that problem was solved. But now I was stuck with this useless bandbrake, or so I thought.

Finally did something about it when I found a thread-on disc brake adapter. Bought that, a Tektro mechanical brake, made a mounting bracket and welded it to the chainstay. It barely misses the sprocket, and wouldn't miss the chain if I tried to mount it elsewhere. Sorry it's a little hard to see.

View attachment 82622

I'm sure you noticed the chain's off. More on that in a moment.

The brake cable was way too long, and I almost cut it but then had another a-ha moment. The extra cable goes into a piece of 3/16 brakeline (or a noodle if you want to use bicycle terms) and up under the rear rack, where it attaches to an ATV brake light switch. So now I have a real brake light (a GOOD one, that uses a real 1157 bulb, not LED's). Picked up the switch and lamp on Amazon.

So the wheel's not orange anymore, what's up with that? I changed the front to a 24 to match the rear, and the ride is a hell of a lot better now. And since the new rim was black (Odyssey Hazard Lite, way overkill but a really nice rim) I changed the rear to black as well. Looks better to my eye. Re-used the Sturmey-Archer drum in the new wheel.

View attachment 82623

Tires are Duro Beach Bum 24x3, with the decals buzzed off. Want to know what really burns me about these tires? The sidewall molding doesn't say Beach Bum, it says EACH BUM. Really, Duro, really? Other than that I really like 'em. A soft ride and nice feel overall.

With more rubber on the road and really good brakes now, I can stop from 25 mph in about 40 feet. Good thing I put a brake light on there.

So guess what happened yesterday?

View attachment 82624

Yeah, the damn input shaft sheared AGAIN, in the same place, My armchair analysis tells me this is probably machined from the cheapest Oriental bar stock they could find, and there's a nice stress riser right where it sheared off, since the other one broke in exactly the same place. My thoughts yesterday were to get a new one made by a machine shop, out of decent steel this time, and with a radius to eliminate the stress riser. But you'd still be pushing 2 HP through a tiny shaft. Might get away with that if you made it from titanium, but I'm not confident in that. So I'm ditching the 5G gearbox for a Grubee belt drive, which should arrive in a week or so.

One last pic, the bike as it sits today:

View attachment 82625

In this pic you can see the battery that runs the lights, the brace for the engine to the top tube, and the PMS (Puke Management System). What's the PMS all about? Well, the HuaSheng crapped the bed after about 20 miles of riding. It had so much blow-by that oil filled the chamber above the crankcase and got pushed up to the air filter. It would leave a puddle wherever it went. This engine isn't a HS, it came from a friend who gave up on it. It's another Honda clone. The only identification I can see is a pad that says BRAND. It runs a lot better than the HS ever did. So the PMS isn't needed (yet). It connects to the engine's breather outlet and separates out the oil from the air vented to the atmosphere. So far all it's caught is water vapor.

Stuff you can't see: A handlebar mounted light switch and key switch, wires routed thru the handlebars, memory foam grips, gel seat, lots of good stuff that makes the bike a real joy when it's actually running.
Where did you get that OHV cover? I might build a bike with a GXH50.
Jul 2, 2018
Been riding the hell out of this thing, and it's still a blast. The engine has loosened up a bit (or it's about to sh*t the bed) and I can now hit 35 on a good day (or rather I could if I was allowed to go more than 20, which would be illegal on my moped plate). But a couple things have been buggin' me.

I got tired of adjusting the rubber chain that comes with the Bikeberry kit, so I replaced it with a nickel-plated heavy-duty chain from ebay. Turns out it's a re-branded KMC chain, which doesn't have a good rep but ought to be able to handle 2 horsepower. I do know it runs a whole lot smoother now. The old rubber chain was pretty floppy, probably due to misalignment in previous evolutions of this bike. We'll see how this one holds up.


So shiny. I left it a little on the loose side.

Next up, the front wheel. I really like the Odyssey's triple-wall construction, but I don't like the narrow width. It leaves a bit of air space above the tube, which is no bueno. It's really hard to find wide rims in a 24-inch size, and the 38mm Ody was all I could find at the time. But I kept digging and found a Felt 50mm wheel. Bonus, it uses a big hub like my Sturmey-Archer drum, so I get spokes as well. The downside, those spokes are painted black. Since I ain't Mick Jagger I spent a few fun hours stripping the paint off them. If you ever need to re-calibrate your pain-in-the-ass-o-meter, stripping paint off spokes is a good way to set the high point.


Ody vs Felt rim width.

The Felt is a single-wall rim, which I'm not crazy about, but it's thick material and my rear single-wall has held up so far, so it'll probably be o-tay. After the spoke-stripping marathon (they're painted, but they are stainless steel) I laced up the drum and now the front looks like this:


The 12-ga spokes match the rear now, and they're stronger than they need to be (although the 14-ga spokes were, too). Now the front tire is just an RCH wider than the rear, but I can live with that. Re-rimming the rear wheel would put the chain uncomfortably close to the tire, and besides that these Felt wheels ain't exactly cheap.

The front feels a lot more planted now, and the extra air volume makes for a smoother ride. That's a result.
Jul 2, 2018
And the evolution continues, down to the little details at this point:


Automatic chain tensioner, made from leftovers. The tensioner brackets are welded to the frame so I didn't have a lot of choice in its location. Time will tell how the welds hold. They're just tack welds since I only needed them for location with the fixed tensioner. I think they'll do, but I can always add more welds and may do so over the winter.


A little paint on the speedo. The clear ring looked a bit cheap. And since this is something I look at a lot, it demanded dressing up.


And a flexible mount for the front of the chain guard. The chain guard has been a problem since day one. I think I got it licked now. Foam rubber sandwiched between the guard and its mount, held in by safety wire.