Kimjon

So today I dragged this out, added a much bigger walbro carb, made a custom manifold to adapt this carb to fit. Then made an expansion chamber...and ended up with about double the power!!!

Then thrashed it for about 20 minutes off and on tuning it...got it dialed it sweet...Then smash!!! I stacked it hitting the tow bar of our family car. No damage to the car, but drift trike - ummmm yeah/nah.

Motor still goes surprisingly. So I may be able to weld up a new bracket to pick up the bolts on another part of the motor?

Oh well, guess it's true..."the faster you go, the bigger the mess".

Exhaust then got VHT ceramic paint

And that's about it for now.

I further milled a step on top to add clearance, and used the dremel to smooth it out

And then installed it, perfect!

Follows the crank, allows a nice wide opening, flow is now going the right direction...think it's getting there now.

Now they fit:

But I don't like the angle, its to restrictive and the reeds hardly open. So hell bent on thinking I can do better than the factory i further milled the base to change the angle.

On to the reed valves.

In my opinion, they face the wrong way in these motors? The air/fuel is dragged in, up and around the massive reed support.

I've flipped them around so that the air/fuel mix is pulled cleanly through them unobstructed. Fingers crossed this is the right idea???

However, problem is they don't fit! So I'll make them fit!!!

Okay...truth be told it was never going to hold how I clamped it above and it moved on me, so take 2 below:

Mmmmm pretty...

Okay...more porting, followed by more porting...

I'll do a bit more on the flow side and then polish it up again.

Piston received a little love. It was black as black can be with carbon build up.

Here it is after 10 minutes sanding:

Still looked shit...so I broke out the random orbital, couple minutes on that, then on the buffer wheel...finally got the dome polished where it needs to be.

That was way more work than anticipated.

Here's a before and after photo to see the difference

And after

And hopefully that equally more flow, and will be one of many things that add up to more power.

Next up for the motor is to calculate its port areas, timing, squish band and compression...then tweak those with yet more porting.

Cases polished

Transfer ports case matched

Roughing it out

Still a bit of work to do, but already a huge improvement.

When I'm happy with the "flow" it will get polished up.

The intake should be rough, the rest should be smooth

Here's a view of the piston placed exactly where it ends up at BDC. note the skirt is to long and the sides of the barrel don't match.

And here it is after matching

Now it's a matter of matching to (barrel) to the cases.

Here it is with the crank and piston installed.

The open style of cylinder with a removable head allows me to port time the motor. I'll stick a degree wheel on the crank, turn it over and measure the degrees at which the ports open and close. Once I have this data, I'll know where improvements can be made.

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.

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

Quick test fit...yup, sweet as.

That'll work.

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!

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

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?

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.

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.

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.

On 1/15/2018 at 20:13, flyingbrick said:

Wheelies must be TERRIFYING

Hell yes! Major fail on attempting that one.

4 hours ago, Kiwibirdman said:

That looks like a lot of fun. 

Would it work to have the chain wheel on the pedals (up top) go down to the original front then a second chain to the rear sprockets. This would give at least 5 gears. It looked pretty high geared to me.

Yes, absolutely.

I was going to do it that way, but thought it would be cleaner this way.

Both ways I could still run a rear derailleur and use the rear cassette, but for what it's for (just for fun) I didn't want to over complicate it.