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

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:

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.


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.


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?


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:


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.
Let's throw some more pics up:


Rear view shows the Amazon brake light and the rear rack (which requires a bit welding and fabrication to fit the Electra frame).


Headlight switch and ignition lock. A bit of safety wire keeps the keychain put, since the switch doesn't lock the key in place. I could put the keys in my pocket or the bag, but this way it reminds me to lock it when I park.

The headlight switch and mount came from Amazon, but the included switches had a flaw: they illuminated in the OFF position, and wouldn't work any other way, so I ditched 'em and substituted one from I don't know where. Had to drill the housing a little to fit the ignition lock. It runs parallel to the kill switch in the throttle, with the wire run thru the bars (which I recommend for both its aesthetics and as a character-building exercise).

If you see anything of interest that's not shown, more pics are available. But as the FNG I don't want to abuse the privilege of posting pics.
Inspired by another member's build, I changed out the rack bag for a leather saddlebag (the Mrs. calls it my "little man-purse"). The rack may or may not stay; I'd like to custom up a tail light/fender mount to move the light forward.


Also put the front fender back on:


And here's a shot of my brake-light switch:


The cable comes off the rear disc brake, runs up thru the tube (3/16 brakeline) to pull on the ATV light switch. Easy peasy.

Still waiting for the Grubee belt drive to show up so I can ride the little booger again.

The problem with not riding it (aside from the obvious one) is that I keep thinking about cool stuff I can do. Somebody talk me out of putting this tank on it:
KOOL ! Bike, like the tires and saddle bag, and all. You will be much happier with the belt drive..........Cur
Here's the final evolution:



Belt-drive install went pretty smooth. I will share some a-ha moments, then more pics.

The spacers under the drive sprocket are not all the same. That means you can fine-tune the location by substituting a fat one for a thin one, or vise versa. A pickle fork (automotive ball-joint separator) comes in handy for getting the sprocket off the shaft. I like the "belt & braces" approach to the sprocket mounting. You have a keyway (with a set screw to retain the key) and another setscrew 180 degrees out that mates to a flat spot on the shaft. Very secure.

The clutch bell is welded to the input shaft, and while the welds look like good quality, I've broken welded bells before. Time will tell. The welds are damn near flush with the surface, so I'm guessing that there's good penetration there and they'll last. Fingers crossed.

Setting the belt tension is a little fiddly. There's a sweet spot you have to find, where the belt is tight but not so tight that it binds. Pretty sure I got it right. Belt tension affects chain tension. Don't overtighten the adjuster screws. They thread into aluminum and they won't take much torque.

You have to tweak the brackets that hold the cover in place, or the screws will shred your belt. Not a big deal, just something to be aware of.

This thing is heavy. Weighs twice what the old 5G chain-drive trans does, probably because of all the steel in it. Steel is good for drivetrain parts.

Okay, enough of that. More pics:


The rack is gone. In its place is a taillight mount, saddlebag bracket, fender brace and brake-light switch mount. Sounds like a big job for a 4-inch muffler clamp, some 3/8 hardline and 12ga steel strips. Booger welds displayed loud and proud. Deal with it.


That Skyhawk sticker had to go. My wife is Scottish, I've been there twice and I love it (hence the name of the bike (Jura is an island off the west coast, home to 5000 red deer, a couple hundred people and the distillery of my favorite single-malt.))

Also, for those who didn't notice it earlier:

I have friend who does CNC machining, and he made me a California-hot-rod valve cover. I like having the only one of something.

Q&A time:
Spare Parts, the tank is on eBay. I actually pulled the trigger yesterday, but they refunded me. Out of stock in the USA. It's a Chinese copy of the tank for a Honda Monkey minibike. Search "monkey tank" and you'll find one like it, maybe even one in stock. There's no info on fuel capacity. The Honda tank holds 1.6 gallons, but an Amazon listing for what looks to be the same tank I ordered says it's way too big. So I dunno. For now I'm gonna rock the China Girl tank.

Arty, the saddlebag came from Amazon. Goat-skin leather from India, 30 bucks. Took me a while to find a bag that wasn't nylon, cost $300, or both. Looks a hell of a lot better than the old bike bag.

Curtis, I sure hope so. For the price of this thing, it ought to bring me drinks.

Enough blabber. Time to go for a ride, it's a beautiful day for it.
Well, it rides great! The belt drive is a true 5:1 ratio, where the 5G chain drive uses a 5.75:1 ratio. So I've got a little more speed, and still enough bottom end to take off easily. Where I usually ride there's a big-ass hill, between 6% and 11% grade. The 5G got up the grade at 15 mph. With the Grubee I should be close to that, but there's only one way to find out. Need a few more neighborhood shakedown runs before I fully trust it; pedalling a 90-pound bike home with that hill in the way is no bueno. Once I'm sure it's dialled in properly and will get me home I'll take the plunge.

Speed is just over 30 indicated, but the front wheel (with speedo drive) is an inch smaller than before, so maybe only 28-29. Fast enough. Engine temps are right in the happy zone, 210 at the plug, 260 at the exhaust port, oil temp around 130. Those temps will go up on a longer ride, but not too much.
Time for a few more little tweaks:


I noticed the chain loosened up after every ride. I know some chain stretch is normal, but it's not growing half an inch every time I take it around the block. What was happening is, the wheel was moving in the frame. Bicycle hardware can only be snugged down so much before it fails, so I made a steel strap from the wheel to the rack mount. Non-adjustable, so no movement is possible. Now the wheel stays put and my chain adjustment is consistent.

Took the plunge down and up the 6-11% grade in the park. Hit 40 mph coasting down the hill, and the disc brake worked nicely. But when I got home, the disc was rubbing the inboard caliper. Turns out my thread-on adapter was tightening itself on the hub, moving the disc relative to whe wheel. What to do?


A little hard to see, but I used nuts behind the adapter to butt against the hub. That should keep things in alignment. Also tweaked the spokes for a little more dish, pulling the tire to the right about 1/4 inch for chain clearance.

Since I'm not a pro bike builder and not building wheels every day, I improvised a wheel stand from scrap lumber:


It's crude, but does the job. By changing it up, it's also a bicycle workstand. Also made dish sticks from 1x2 scrap and a couple of drywall screws.

Coming back up the hill, I made 15 mph on the steepest portion, The engine was bogging down with the load, but didn't drop below 15 mph or get too hot. Also, the Grubee sounds like a supercharger.