Common problems with triples and how to solve them
The above is the condition of the exhaust port of the H1.
As expected, the top and bottom of the port have been severely worn down.
Even after boring, the black area have been worn down so much that they are concave,
so the blade cannot reach them like the silver area.
I think this dent is due to the piston rings jumping into the port and moving up and down, which wears down the top and bottom of the port.
On the other hand, the photo below is of the exhaust port of a Honda cylinder.
Honning has been completed and cross-hatching has been done. What I want you to see is the EXHAUST port, which is much wider on both sides than the H1, the pillar (bridge) standing in the middle, and the oval gray area around it = the state of the relief processing of the pillar.
Larger EX and IN ports can suck in and expel a lot of mixture at once. This definitely improves the power output of a two-stroke engine.
However, if the port holes are made too large, the rings and piston skirts will jump into the port. This is exactly the problem that the H1/H2 triples have.
Previously, it was said that the size of a 2-stroke port must be at most 67% of the bore (inner diameter size).
This is to prevent rings and other objects from jumping in. However, the H1/H2 ports are exactly 67% of this size. This causes abnormal wear, as shown in the photo. On the other hand, such problems do not occur with Honda cylinders. This is because there is a pillar in the middle, so rings do not jump in. Even if the port width is expanded to 100%, if there is a pillar in the middle, the size of one port is only about 45% of the bore after subtracting the width of the pillar. Therefore, there is no need to worry about rings jumping in at all.
Honda's so-called "T-port", as seen in the photo, was an attempt to solve the problem of the limit on port size.
Another advantage is that if rings jump in, the shape of the port must be oval and sagging to push them back toward the inner diameter. However, if there is a pillar, jumping in does not occur, so the upper edge of the EX port can be designed to be almost straight. This also has the advantage that exhaust gas can be released all at once when the piston goes down.
When HONDA first started racing with two-strokes, iB had the opportunity to help them manufacture cylinders for the RS125/RS250 and other models. And thanks to our masterful execution of this "pillar relief" processing, which other companies had trouble with, we were then able to take on the task of machining all of HONDA's two-stroke spare cylinders. I'll be sharing this proud story in detail somewhere in the future (^^;;;;
Anyway, this is iB's biggest hit technology among the two-stroke cylinder processing that we specialize in.
If this "pillar relief" is not done correctly, heat will concentrate on the EX port, causing the pillar part to expand and quickly seize up. It seems that HONDA also struggled with this problem in the early days of motocross and other models.
And because HONDA held a patent for this port shape, other manufacturers could not use the same port shape, and HONDA always had the advantage in terms of two-stroke power output. This was such an important technology that it could be said that they had the power to make the H1/H2 a better engine. They say that Honda has the power and Yamaha has the handling. It may be fair to say that the cause of this was here.
By using this technology, we could solve the problems that the H1/H2 had. That's what iB thought. The patent had already expired, and it seems that SUZUKI and Aprilia had similar ports in the final period of 2-strokes.
To do that, we thought we could make a sleeve with pillars by machining it, and then cut off the standard sleeve and replace it! We're good at making 2-stroke sleeves! (^o^)
With this technical background, iB decided to seriously tackle the problem of abnormal wear on the H1/H2.
Sorry for the long post. m(_ _)m
to be continued.