Kimjon's not as cool or epic as Muncie's off-road goped Bigfoot scooter thingy

[Kimjon 752]

In a confined space its always hard to get an overall impression, so I pushed it outside for a first real stand back and admire look at it.

[Muncie 2,662]

Sprockets and chain are on their way to you. Looking good that exhaust shaped up well little muffler looks sweet where it is.

Envy the ability to transport this easily in say a car......

[Kimjon 752]

Yeah, I'm thinking total weight about 5kg? What's yours weigh;-)

Oh and thanks for the sprocket and chain...you're a GC Muncie!

[Muncie 2,662]

Haha engine alone is around 45kg on mine not to mention the 10mm plate I mounted it to hoping it wouldn't pretzel up. Think I'll build a lightweight one and tow it on a tiny trailer behind the big one. 

 

[Kimjon 752]

Added a fender. I'm using a mini quad rear mud guard which I had to trim down about 20mm, but otherwise a perfect fit.

Here I'm setting the angle I want it to be, then welding it in place.

And fitted in place.

[Kimjon 752]

To adapt this to run on a sprocket (which it was never intended to do), I machined up some spacers that will set the gap between the tyre and the sprocket.

These are all exactly 44mm long, which is the required distance from the hub face to the inside face of the sprocket.

A long bolt will hold the two wheel hubs together and carry on through the spacers and pick up the sprocket.

[Muncie 2,662]

Does it go yet? 

[Kimjon 752]

1 hour ago, Muncie said:

Does it go yet? 

Nope. I'm waiting on a diaphragm carburetor and manifold from eBay, this will allow me to mount the petrol tank lower than the carb. Once that arrives it should be a goer?

In the meantime it's still rough looking, so I'll keep chipping away at making the roughness disappear

If you're worried about racing...I have plenty more to choose from...

[Muncie 2,662]

3 hours ago, Kimjon said:

 

In the meantime it's still rough looking, so I'll keep chipping away at making the roughness disappear

If you're worried about racing...I have plenty more to choose from...

Not the racing I'm worried about it's just the high risk of death and injury from the shit I've built. At least it has polished rocker covers now for people to chat about while they hose me off the racetrack.

[Kimjon 752]

Okay, got a bit of spare time last night to break out the die grinder and start porting the motor.

This is the before, look how rough those ports are...the chamfer looks like it was chewed by rodents!!!

It would still work and that's how they all look inside. Fundamentally these are good motors, the only thing letting them down is the QC (lack of) before sending it out the door. With a bit of work you can make them pretty tidy and add a bit more horse power in the process.

[Kimjon 752]

I made a paper gasket then marked out the port shape. Very much a case of trying to fit a square peg in a round hole! But the pulse back from the expansion chamber will love this smooth(er) transition, and make more power.

Then realised that I could just use a circle template to do the same thing

I ported, then kept checking with this template that all was good.

Happy enough with this for now.

[Kimjon 752]

Then I made sure what's left of the gasket contact surface was given the best chance of sealing by sanding it flat.

Next I stuck the cylinder in the lathe and made sure the sealing surface was true by turning a minute skim off the face.

Then test fit the head.

All's going to plan so far. I'll attack the bottom end tomorrow where I'll make some big changes.

[MaxPower 439]

hey I've just brought one of these stand up scooters off an old mate for $100 with a stuffed 25cc motor, is it a mish to fit a generic 50cc engine from trademe to one of these? had one years ago was great for going to the pub and stashing round the back. 

[Kimjon 752]

42 minutes ago, MaxPower said:

hey I've just brought one of these stand up scooters off an old mate for $100 with a stuffed 25cc motor, is it a mish to fit a generic 50cc engine from trademe to one of these? had one years ago was great for going to the pub and stashing round the back. 

Put up a photo of your one so I can see what you've got?

[MaxPower 439]

pick it up on the last weekend of the month will put up a pic then

[Kimjon 752]

Shouldn't be hard to do. But may be easier with like for like?

[Kimjon 752]

Im jumping back and forwards a bit, but that's the reality of these projects. I tend to do as much as I can until I hit a barrier that stops me going any further...Then jump ahead and work on something else, to prevent losing momentum.

So in saying that, back to the sprocket:

I traced the brake caliper, as this will share the same PCD as the sprocket. Much easier to work with on paper, and soon I had the spacing sorted.

I drew circular guidelines to locate the sprocket.Then used the centre to take all measurements from. I blacked out the area and scribed a diameter 65mm circle.

This sprocket had 68 teeth, so been a nice even number the quarters equaled to 17 teeth.

68/4=17

And that split the diameter 65mm circle into 4. Giving a mark to centre punch and drill.

Sorted!

[Kimjon 752]

Quick test fit...yup, sweet as.

That'll work.

[Kimjon 752]

Jumping back to the motor.

This motor was a $20 buy off trademe. It came on a totally fucked pocket bike, that was stored outside with no spark plug in the motor for God knows how long? In that time the motor filled up with rain water.

I turned it over by hand and it pumped the water out. Luckily the oil in the 2-stroke mix saved the internals. But the bearings are toast!

I used an old clutch to make a gear puller to remove the clutch on this motor. It was well stuck...but this tool popped it right off! With that out of the way, I stripped the motor right down.

Externally its really suffered from its poor storage, but internally it all good. I'll probably sandblast it after porting, so it will look like new and its dirty past will be something we both pretend never happened

 

[Kimjon 752]

I'm going to flow the bottom end by porting/blueprinting it. Things like this lip the cylinder makes as it protrudes into the lower case will be reshaped to "seamlessly flow".

The arrows I've drawn on indicate crank rotation.

That sharp shelf in the photo above will receive a lot of work in this area. Any area like this will create poor flow due to an eddy forming in the low pressure area. The basic idea is that a motor is simply an air pump, and the more efficient that pump is...the more power you'll make.