Chris-PA
Where the Wild Things Are
Also, if you have an old shot clamshell engine and access to a bandsaw (or you feel like using a hacksaw), you can make a nice tool to help visualize what is happening in regard to port timing:
Porting Saws on the Cheap
- Thread starter Chris-PA
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Chris-PA
Where the Wild Things Are
A note on port timing measurements - I almost never bother to find TDC. The port events on a piston ported 2-stroke are always symmetrical, so I just measure duration. I rotate the engine until the port just starts to open, then set the degree wheel to zero. Then I continue to rotate the crank until the port just closes, and read off the duration. I plot the timing events like this because it helps me to see what is happening:
There are many strategies for port timing and widths and shapes of ports, and I don't intend to get into that. Keep in mind that the wider the ports the more the ring will pop into the port opening as it goes by, and the more careful you need to be with beveling edges - so if that is difficult with your tools you should give it consideration.
Also, if a particular operation is difficult, such as raising transfers in my case, then you need to adapt your strategy around that. I've only raised transfers a couple of times when I really needed to. If the transfer timing is staying put, then that will dictate intake and exhaust timing depending on how you prioritize other factors.
There are many strategies for port timing and widths and shapes of ports, and I don't intend to get into that. Keep in mind that the wider the ports the more the ring will pop into the port opening as it goes by, and the more careful you need to be with beveling edges - so if that is difficult with your tools you should give it consideration.
Also, if a particular operation is difficult, such as raising transfers in my case, then you need to adapt your strategy around that. I've only raised transfers a couple of times when I really needed to. If the transfer timing is staying put, then that will dictate intake and exhaust timing depending on how you prioritize other factors.
BigRed96
ArboristSite Operative
Will be watching this thread.
