Kimjon

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.

Hell yes! Major fail on attempting that one.

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.

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...

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.

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.

I used a pit bike exhaust like this on the "Mike-trike" and it sounds amazing! https://m.ebay.com/itm/Pit-Dirt-Bike-110cc-125cc-140cc-Performance-CNC-Exhaust-Pipe-System-Muffler/112543077898?hash=item1a3417160a:g:lt4AAOSw4INZo97Q Soft quiet idle, then roars like a lion at WOT. I only paid $33 with free delivery from China door to door. It keeps the obscene noise levels down for neighborly relations

Another way of adding rake/trail is to put tabs on the front of the fork ends like this: This would enable your handlebar stem/post to be more upright, giving you more room on the deck to stand. You can still lower the ride height etc this way.

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!

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.

I welded up a few ugly holes, added some more bracing for strength.

On to the front end. This gem was left outside for many years. I know, hard to tell...but you'll have to take my word for it I'm sure it'll buff out, no seriously...fuck it, let's give it a go and see? Boom!!! Not to bad.

These chambers vibrate like hell, and eventually this will fatigue the metal. I added a support bracket, and a little tab to the muffler as well. Here's how I made the support bracket. All welded, and the muffler tab added too. This metal is super thin and a challenge to mig weld. You'll be going good like a welding God, then it blows a huge hole...but that's the game we play.

Ouch!

Waiting around isn't one of my strong points, so to move this project forwards, I welded it straight this morning. I think it looks the part

A couple more pics. the cardboard is a mockup of a rear fender I'll make/add. And the yogurt container is there to help me visualise a gas tank. Next up: I'm going to port the motor and add a larger carburetor with a diaphragm pump, so I don't have to mount the tank higher than the motor, then tidy it all up.

I cut a port in the main pipe with a step drill to match, and welded it in place. Once again using a string line to centre it. Then I closed of the tip of the cone where the old muffler was, as the exhaust will no longer exit there. I'm going to curve it around and point it down towards the ground...but I couldn't help taping it on just to get a feel for how its going to look. I'll give it more time, as this look is growing on me. I may just weld it up like this?

Then I fitted the muffler. I cut this off another pocket bike, welded an extension that was approximately 60% the size of the header pipe diameter to restrict exhaust flow.

Going for a centrebleed pipe, so marked out location of bleed port. String line gives a centerline, just mark each side of the string. then find the tangent and mark that.

So, some rules of thumb. The longer the header, cone/s and barrel length are the broader the power band will be over the useable rpm range, but less intense. Inversely: a shorter header, cone/s and barrel length gives a much sharper and more aggressive power band, but this only happens at a higher rpm. For this project running a centrifugal clutch, I'm keen to have a broad softer starting power band with a wide midrange. Well that's the theory...reality check to come.

I feel like I'm winning on this one now, as the expansion chamber starts to take shape around the rear end. Cut, shape and tack: And then welded: I need to pick up a large bend to tie it to the other cone, but I have a plan (mates scrap bin)

Struggling to get the shape I want, but nothing a hacksaw, welder and some more thinking time can't solve.

On to the exhaust expansion chamber (yes that rather rusty one in the above photos). There's an entire science dedicated to these...and I've used none of it "designing" mine. What I have is a reasonable past history with 2-strokes, so I'm simply going by what feels right. At the end of this project I'll soon know if I did the right thing or not?