Dutch minibike build.

#23
The engine mounting plate is made out of 20mm thick aluminium. 260mm long and 120mm wide. Slot holes for the engine/chain adjustment and slotholes from side to side for chain alignment. This alu plate will be mounted on fixed supports that are welded to the frame and they have enough holes in it to place the engine where I want it.


I bolted the supports to the plate, and welded them in place. After some accurate measuring.


The bottom side of the engine mount.


With the engine mount in place, I just had to put an engine in.

Because of the stock exhaust and intake the gastank is mounted in this position. That might change in future.


I also installed a clutch. "inboard" is what you call it. This way the engine is almost centered of the bike. I have modified a washer to "fill the gap" between the clutch and engine. It now has a chamfer in to fit the crankshaft. At the moment the clutch is not floating. Should it be floating?

Because the bike needs a seat and other parts, I ordered some parts at a Dutch moped shop. There was a seat which had a bit of a rounded, triangle shape and almost the right dimensions (and reasonable price), so I ordered it. It already arrived, along with cables and other small parts. Seat looks good (pictures will follow) and I already made a mounting bracket for it and welded it to the frame.

I'm waiting for the brake discs to be lasercut. But at this time I can figure out how to connect the throttle cable to the engine. I want the cable to "exit" the engine on the backside, close to the rearbrake caliper, so both cables can be routed together.

"Stay tuned"
 
#25
I had a day off of work today.
Today; the fuel tank mount is welded to the frame. The seat is placed onto the bike and I welded a tube to the frame as footpegs. I like to have foldable footpegs one day, but for now, this will work. Also the twistgrip throttle is connected to the engine.

Problem: Engine idle rpm was around 2000 rpm (bad). My throttle cable wasn't causing it. Idle adjustment screw didn't do nothing. It looked like the governor was not closing the butterfly completely. It wasn't touching the idle adjusment screw on idle. When I manually pushed/pulled the governorarm to idle position, the engine ran slower on idle (good).
There is a spring around the linkage from governor arm to butterfly/carb. After I unhooked this, the idle rpm was ok. I messed some more with the governor arm/shaft adjustment, trying to get it right with the spring on...But didn't succeed. At this time, the spring is off, it is gorverned and full throttle rpm is at 4200rpm.

Meanwhile at work, my new brakediscs and caliper mounts had been lasercut, so I picked them up. I want to have it riding tommorow.

Pictures:

Fuel tank mount adapted to the frame.


Twistgrip throttle and brake lever mounted.


New to this, but after a lot of adjustments, getting there.

Stay tuned
 
#30
News update: It's in running condition!
Wow, what a fun it is to build and ride such a minibike!
As I mentioned earlier, the brake discs had been lasercut, along with the caliper mounts.


Frontdisc: custom made, 180mm diameter, 3mm wide. Perfect fit with the frontaxle assembly.


Reardisc: custom made, 180mm diameter, 3mm wide. Perfect fit with the rearaxle assembly. Bolts have just 1mm clearance to the frame.


With a front sprocket of 15T, I choose to mount a 90T (#219 chain) sprocket on the rear. 1:6 ratio.


After drawing caliper mounts in CAD, they have been lasercut. I couldn't have done it better with a grinder.:grind:


These are "foating" calipers, but I had to change a bit on them, because the bolts, that let them float, came in contact with the brake disc. Fixed the problem.


Dutch minibike, ready to rumble...


My oldest daughter having fun.


That would be me.

Today it drove for the first time.

-I choose to go with a 1:6 ratio. As I didn't have any bigger rear sprockets, just smaller. And I thought it would be easier to shorten a chain as to lengthen it. (if I ever consider a smaller rear sprocket)
-This ratio is just about right I think, after today's riding. The hour/tachmeter registered 3 hours of driving. I have to mention that this tachmeter isn't very accurate.
-The clutch is a bit noisy when it's slipping (a bit of metal scraping sound-ish), once it's locked, the noise is gone.
-A lot of vibrations, as there is zero suspension. Maybe, tires to much inflated.
-Taking turns is easy, it handles just great.
-It outruns a 110CC quadbike, flat out.
-Overall; pretty happy with how it turned out.

All it needs now are the final touches.
"Stay tuned"
 
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#32
Looks like your daughter is having a great time on the bike. It is interesting to see your home in the Netherlands, I like to see the different architectural styles around the world, especially Europe. Also, it is nice to see who the builder is. Great build, nice brakes!
 
#33
Thanks for the compliments.
It isn't finished yet. it needs some small tweeks and fenders.
I noticed the chain does hit the engine mount. Even if the chain's tension is about right and I can't push the chain against the support manually, it seems it does hit it, during riding.
I will make a small roller out of some plastic/nylon piece and with a spring it will keep the chain tensioned, up and away of the enginemount.
Idea is to mount it to the engine, which will make it perfectly align with the chain at all times.
Stay tuned
 
#34
Nice build..:thumbsup: a chain tensioner is a must have ..you'll get some chain stretch and you wont have to shorten chain or move engine around so much..most mount them to the frame ..minis are super fun and easy to care for...enjoy
 
#35
..minis are super fun and easy to care for...enjoy
I agree, it's fun.
Tonight I took the standard exhaust of. Made a new flange and welded an open pipe to it. Now it's making beautiful noise.
When driving at full throttle, the engine stops making power for about a second and picks up speed again after that, until it holds back again... It is the governor, which closes the throttle a bit, when at full throttle. Something there is just not working properly. Needs some adjustments or something.
I found and downloaded a shop manual for GX engines, will have to see, what's in there...
Gr,
John
 
#36
May be the governor..what fun in having it control your throttle..people dislike taking governor out coz you could blow the engine and possibly get hurt if blows..i just use a tach and keep it below 4500 rpm..yeah safest is to put billet rod and flywheel but i don't wanna do eng work these are utility eng ment to run 3600 to perform work with longevity.to me it's like my boat 2 stroke that has no governor and I'm not going to peg the throttle till it blows..it's up to you..if you want to be safest either leave it governed and deal w the surging or put billet flywheel and rod to run high rpms with less chance of blowing it up..it is possible you could adjust springs and get a little more than 3600 on that large governor arm
 
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#37
First a picture of the exhaust, which replaced the stock exhaust.


It's made out of 25mm tube. And flange is made out of a piece of 6mm thick steel.

Well, about the shopmanual I downloaded from internet; It's not complete. It's missing the last 4-5 chapters. I can't seem to find a complete downloadable shop manual. So a lot of info is to be found on internet.

About the surging. It is solved, but now there's another "problem"...
What have I done? I took airfilter off, in such way I could take a look inside the carb. When I moved the governer arm full throttle, I noticed the butterfly in the carb wasn't fully opening.

Butterfly isn't fully opening. This is before the static governor adjustment.

I performed a static governor adjustment.
Butterfly is fully opening after that adjustment.
I started the engine up, it was idling to hard, but I took it out for a ride. It doesn't surge anymore, but it's not making the rpm's it used to do. I guess it's now making the rpm's (3600) it was designed for.
Before the adjustment it was making a lot more rpm's and running faster, but surging...
It's running, not surging and safer for kids to ride. Now I need to get the idle rpm down. Which is to high because of the governor arm, pulling the throttle.
 
#39
That sounds odd...i wonder why it would make less rpms with the governor removed.
Sorry if my English isn't that good, but the governor isn't removed or has ever been removed. I meant to say that because of the surging problem, I performed a static adjustment of the governor. This did cure the surging problem, but the engine wasn't making as many rpm's as before the static adjustment of the governor. It was making over 3600rpm before the static adjustment (with surging).

Today I went for a ride again. No surging, probably 3600rpm at top and high idle rpm.
I took it back in the shop and adjusted the governor a bit. Nice idle rpm, well over 3600rpm at top, but surging.
It outruns a moped which drives 50km/h. With the tires and sprocket ratio I have, that would mean around/over 4500rpm with governor installed and functioning.
 
#40
Li'l Popeye, you are too humble about your English abilities. I was immediately impressed with your English, very good I say. I once knew a Dutch lady who, after being in the U.S. for maybe ten years, was hardly recognizable as someone who wasn't born speaking English. I have seen Dutch people on TV who seem like her. Is this common?
 

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