Cutting I have a good start on the cylinder porting. I removed many casting flaws and drilled the auxiliary intake ports. I'll match the barrel to the block using the lines I scribed earlier. I need to run some numbers with two-stroke software to help determine the final dimensions of the ports. Since the exhaust port is already at 64% of bore width I doubt I'll widen it much if at all. The intake ports "look" like they could stand to be a little bigger.
The intake port has been cleaned up. Compare it to the photo in Part 2 (4th photo) to see the changes. The auxiliary intake ports have been drilled. I did not narrow the intake bridge. There's still more work to do on this port.	I made the holes oval instead of round in order to conserve as much material around the cylinder base hold down studs/nuts as possible. There's plenty of material left so I won't worry about their ability to hold the barrel down and seal it.
The small port feeds to this area of the transfers. They're most useful when the tuned exhaust is sucking mixture out of the crankcase. They will allow some additional flow. Is that a 1 mm thick base plate spacer ?!?	The transfer port area has been cleaned up. Compare this photo to the photo in Part 2 (6th photo). The focus has been on smoothing things - not changing them. The black area reveals a dip that's below the surface - I did not chase it.
Porting I went over the painted surface of the ports with cutting tools. Along the way I was able to smooth things out a great deal. The sharp edges, lips and ridges are history - they have been replaced by rounded corners. Though I cut the liner pretty thin at the bottom (see these pictures), I put a generous radius along its top edge. There are a few black spots left. These are areas that did not clean up with the porting operation. If there had been any real bad pits, dips or valleys in the port walls or tunnels I would get out the epoxy, fill them and grind them flush, but there wasn't really anything that caught my attention enough to warrant using epoxy this time. I used the carbide tools to remove the nasty edges near the liner and the diamond tools to finish the surface. The diamond tools leave a bright looking surface when done but it's a little misleading - they leave more "tooth" than it appears. Running my finger across the surface reveals the direction of the grain. Many times transfer ports are cut and finished with carbide tools. I like the finish the tools leave when the proper piece of carbide is used. As a general rule a tool with few or no cross cuts in its surface will leave a smooth finish and those with some or a lot will leave a rougher texture. Some carbide cutters have many cross cuts in them and leave the surface with a very discernible texture. When using these tools it is especially important to keep them moving as they bump their way along - stopping while the port tool motor is running will leave a gouge. Working the tools properly will yield a grain that can work to advantage in either set of transfer port tunnels. When I say advantage I am referring to letting the mixture either run across the grain or against the grain. It's a small thing but letting the mixture go with the grain wastes the time spent on texturing the port walls. The diamond tools can be turned either way so getting the grain to line up the way it works best is very easy. The port tunnels are a lot easier to see when the black paint has been removed from the surfaces. I can now see the shape of the tunnels and their aim much more clearly. The main transfer ports are cut well ahead of the port window and are angled back very far to release the mixture well behind the center of the bore. They have a good amount of port wall taper to them (Bernoulli's principle) to keep port velocity high. These are good ways to keep short circuiting of the fresh mixture to a minimum. The tunnel has a substantial amount of arc to it and ends with a flat top. These designs are power range widening. The secondary transfer ports have much less arc to them and end with a slight upward angle - only a couple of degrees. They'll release the mixture a little higher in the cylinder because they have have less curve to their tunnel. The rear port wall "kicker" is substantial - it shoves the mixture toward the center of the bore. A design like this limits the amount of collision realized by opposite port pairs. The boost port is ordinary in its design. I drilled the auxiliary ports using a 1/8" Cobalt drill. I entered the material from the transfer port side and drilled toward the intake area. Because I wanted the new ports to be oval I drilled 3 holes on each side - on top of each other, and tied them together by working them with a ball end diamond tool. I made the port walls taper inward (top to bottom) from the intake side to the transfers and I gave them a bell mouth on the intake side. The finished ports are 11 mm tall by 5 mm wide. The bevels that are on the ports inside the bore were put there the last time the cylinder was bored - see the Thread Spread article about it at http://www.macdizzy.com/blasterpwr.htm. The victim of a midrange meltdown. The person who bored and beveled it could have used a smoother cutting tool - but I was able to smooth them out a bit using Cratex tools.

Date Last Modified: 8/8/99
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