Dutch minibike build.

#1
Hello,
My name is John, born in 1976 and living in Netherlands. Small country in Europe where "your minibikes" are very rare. Ok, we do spot a small Honda once in a while. And those Chinese pocketbikes you get when you do grocery shopping;-)
I have a Chinese pocketbike, too. And when it broke down and looking for parts I ended up here. Seeing all those nice, 4 stroke engine powered, bikes and builds. It got me thinking; I want that, too. The Chinese pocketbike is in running condition again, but it's litterally a pain in the @ss. Also another reason to make me (and my daugthers) a real minibike.
But rare as they are, I will build my own from scratch. I'm not making an exact copy of 1 special brand/type, but will be snitching several ideas of this forum.
If anybody recognises his idea in my build; Thank you! Your idea has made it over the pond...
Really; thanks! Great forum, with loads of nice stuff to be found.

Details of my to build/drawing:
Engine: Honda GX 160
Tires: 145/70-6
Wheelbase: 890MM (yes, Dutch metrics.../25,4=...")
Rake: 30 degrees
Trail: 85MM
Center to center bottom and top tube: 450MM
Handlebars height from ground: 890MM
Main tubes diameter: 26,9MM (better safe than sorry and a more ridgid look)
Chain: #219
Sprocket front: 15T
Sprocket rear: 75-85T

If someone has any remarks, tips, or knows I'm way of in measurements, feel free to let it know.

For the build I have enough tools, like a mill, lathe, TIG & MIG welder, etc. Anything to make a nice bike.
Enough text for now, here are some pictures:


3-D software makes life a lot easier.

I bought 3 of those Honda GX 160 engines.

145/70-6 tires and 6" rims.

Getting a frame together. (at this point it seemed smaller as I imagined, altough I got some measurements from some threads here)

Head tube ready to accept some bearings I have somewhere in a pile.

Front/forks getting together.



I wasn't able to take a picture and sit on it the same time... (this is more comfortable as to a Chinese pocketbike)

More parts have arrived and drawing is getting upgrades. Sprocket adapter, axles, etc...

At the moment I'm a bit in a struggle with designing sprocket and disc brake adapters to fit my wheels. As I don't have the sprockets and discs yet. It has to be something solid, straight and easy to make.
"Stay tuned"
 
#2

Milling some bend up tubes to a perfect fit. Milling gives no dust compared to grinding and makes life easier.

Added some extra tubes. The tube on the back end will be handy to lift the bike. I guess that's what they are supposed for?
 
#8
Thank you all.
Today the rear sprockets and #219 chain came in. I had ordered several sizes of sprockets, because I don't know which ratio will be best, with the standard GX160 engine.
Clutch which I already have, has 15T. The clutch is probably a Chinese one. Outside looks like the Max-torque clutches I've seen in some posts. Well, it doesn't hurt to mess up a Chinese one in the beginning. When the bike runs ok, I can always skip to another clutch.
The aluminium rearsprockets have 70, 75, 80 and 85T. At 3600rpm the minibike will go between 40 and 50 km/h (25 - 30mph) depending on rear sprocket.
After the sprockets arrived I measured them, bolts pitch circle and mounting hole. I needed those measurements to complete the next drawing.

This will become the rearaxle, mounting hub (what's it called?).
I have been searching through a lot of posts and pictures and I came up with this. Which will fit my wheel best.
Basically it will be a 50mm tube from side to side. In the middle a support for the wheel and on the sides a support for sprocket and brake. All 3 support will slide over the tube with a tight fit. That way they will be centered and straight, I hope. Sprocket and brake will be centered on the supports, too. And in that way they will be centered to the tube also. The supports will require just a little bit of welding to the tube. Maybe tag welding is enough.
With the lathe I will make space for some ball bearings on the tube ends.
Tommorow another day of holiday.
"Stay tuned"
 
#12
Thanks all.

Shipping costs to the Netherlands (including taxes etc) and the fact I like to build my own bike/parts, is probably a reason I'm not riding yet. But the greater the satisfaction will be whenever I am (or my daughters...). I get more satisfied by the building process as to riding.
For brakes, I've been searching, and really liked the "clutch drum brake" idea. Still I didn't choose to go that way. I want front and rear brakes and I've heard that most braking capacity comes from front brakes. If my daughters are going to ride, I want the brakes to function properly.
I couldn't find any discs that would fit my axle assembly as drawn. I did find some discs for €15,-/each, but they were to wide and needed work to make them fit. Others that might fit, were to small in diameter.
180MM diameter, 3mm wide, is what I was after. I already have some mechanical calipers, so the discs have to match.
Next week holiday is over and I will have some custom made discs lasercut at my work (at least whenever they have time to do so). That's the easiest way and probably the cheapest way, too.

Calipers, sprockets, chain and some bearings.

Today I've worked on the rear- and frontaxle assemblies.
"Stay tuned"
 
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#13
Clutch drum brakes don't work if chain comes off..dual back and front discs ok if you got lever w dual cables..or a rear foot operated scrub brake and a disc up front w a single cable lever..with your skills you got options..bike sure to stand out and be different there:thumbsup:
 
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#14
Clutch drum brakes don't work if chain comes off..dual back and front discs ok if you got lever w dual cables..or a rear foot operated scrub brake and a disc up front w a single cable lever..with your skills you got options..bike sure to stand out and be different there:thumbsup:
It will get front and rear disc brakes (not so different). Operated by left and right levers from a Tomos moped. I got them today at a local bicycle store. "Supported the local guy".
 
#15
It looks like you have things working properly. Very nice design & execution! 100cc4.jpg

A rear brake is good to have, a front one also. At higher speeds, the rear brake is what you want to use most of the time. I was listening to a conversation on a tech inspection of a motorcycle at Landspeed Racing (Bonneville) this week & heard the inspector tell the rider to NOT use the front brake at high speed, just the rear one. At lower speeds, the front does more work.
 
#16
... I was listening to a conversation on a tech inspection of a motorcycle at Landspeed Racing (Bonneville) this week & heard the inspector tell the rider to NOT use the front brake at high speed, just the rear one. At lower speeds, the front does more work.
I'm not trying to break any landspeed records, yet... ;-)
For the next build (I think there will be another build coming up) I will make another design for the front and rear axle assemblies. This takes to much time on lathe and mill. Yes; I can say it's got "billet" parts, but it took me a couple of evenings to manufacture the parts, that nobody will see.
It's designed that it will accept the rims I have, the sprocket (which is exchangeble with many others) and a disc (will have to be custom made). And all has to be solid/straight to prevend any chain issues.
Today I got the parts assembled together. The "carriers" are shrink fit on a tube. Just a bit of locktite in between to prevend corrosion.
Pictures:

Fabricated parts for the front- and rear axle assemblies. (the connecting rods are not for the minibike...)

Heating up parts for shrink fit.

It fits!

Checking if anything is out-of-round after tack welding... Nope, as straight as it gets!

Tires were mounted on the rims after the picture was taken.

These axle assemblies will house ballbearings and a solid shaft will be made to fit in it and provide a spacer for the bearings. This solid shaft will be mounted, between the forks, with a bolt on each side. This way I can use plain bolts, instead of very long bolts, with a seperate spacer.
Anyone tried/made it like this? I think it's as safe as with 1 long bolt.
"Stay tuned"
 
#17
Hello,
I've got a rolling frame!
I have made some rearaxle mounts en welded them in place. Mounted the wheels and I got myself a rolling frame.
Still some things to do.

I had to measure a lot, just to make sure the axle mounts would be positioned okay.

Positioning the axle mounting plates.

Rolling frame.

Maximum steering angle.

Maximum steering angle.

"Stay tuned"
 
#18
Hey Popeye, nice to see your build on this site. I look forward to seeing your finished project. I see you have a good old American Bridgeport in your shop.
 
#20
Thanks!
I know it's not an exact copy of any particular original minibike, but I tried to make it look like it. It has got something of diffrent brands/makes. You'll notice it looks like a Lil indian, but it also has some Doodle bug and Fox sprite touches to it.
My goal is to get that "vintage" look US minibike with modern parts like disc brakes, and engine, which will be a Honda GX160.
When it's done we'll start riding unpainted. I know there will be some issues that need grinding, welding or something else.
 

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