Kimjon

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?

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.

Hell yes! Major fail on attempting that one.