Long ago when I first got into 2 cycle bikes one guy I met had been at it a few years. He even worked in the summers of his high school year as a tech at a Kawasaki shop. I was a bit older than him but I learned loads from what he showed me.
The Dremel or any of the knock offs of it are handy. There are battery powered ones and swivel head models but his was a ball bearing high speed job. He had grown rather handy with it too. It seems he started with cycle magazines that showed how to tweek the Japanese piston port bikes which he was able to buy cheap as they were older.
He showed me an article on cylinders that detailed sizing and matching of ports and the photos showed the transfer ports and the other ports that were important to work on. It seemed the production finish was rather imprecise in those days and the article showed showed pictures of using a new piston to hold up in the bore of the cylinder (which was off the engine) and using a scrib to mark the bottom of the ports even with the lowest port and again the same way at the top by placing the piston down from the top of the cylinder. This used the piston edge like a straight edge to align the tops and bottoms of the ports exactly even. Then the Dremel tool was used to grind to the mariings and then relieve the edge so the ring wouldn't get caught on it. (basically rounding the edges of the ports outward away from the cylinder wall)
The reasoning was that all the ports would open or close at the same time as the edge of the piston dropped below the edge of the ports or rose above them. There were some tapered guides just behind the carb leading into the cylinder that he would smooth up and even whittle down a bit. Thus fuel air entry flow would be more streamlined. It's already been mentioned to match the intake ports, gasketts, and manifold to the same size so all is a smooth transition.
My buddy even had a half dozen new spark plugs he would torque into the head (which was off the engine) to check and inspect each one to see if any of the reach extended into the chamber. I actually saw him touch up a few and smooth them even with the head. Some of his bikes had rotary valves and some even had reed valves. With those he would shave the rotary valve back on one or both sides with his Dremel tool. I don't know if the Chinese are offering this technology yet, or just staying with the cheap and dirty little piston port 2 strokes. Reed valves seemed to be adjusted with a feeler gage to where they were tweeked to his satisfaction.
I used to go with him to the motorcycle drag races and help get the three bikes he raced on and off the trailer. He had this "OLD" Kawasaki Big Horn one cylinder dirt bike that he had installed a big bore piston kit on and changed the gearing. This thing looked like it had been drug out of a dump it looked so bad.....but he had smoothed up the ports, worked with the rotary valve and and a "torque tube" expansion chamber. He would run against Honda four cylinder bikes and beat them consistantly by a foot or two.....but he won. Talk about some angry Honda owners and a laughing crowd of spectators. I mean I don't think a self respecting dog would have chased after his old Kawasaki. But all the tech tweeks were on the inside where nobody would expect them when they looked at the outside.
But all this was back in the early eighties when I was first learning about this stuff. That's when I learned how much difference a Dremel tool could make.
Give this page a look.
Engine Modifications
