670 ctlinder design

[oldsaw-addict]

Has anyone else here ever taken a 670 apart and really looked at the cylinder on the saw? I did this a few days ago and I found that there is a set of 2 ports on the cyl. walls that I dont understand the reason for their existence.The reason I dont understand them is they are on the lower 1/3 of the cylinder and one serves no obvious purpose while the othe one, I think is the air intake from the carb. Can someone help me out here, I mean what the HECK are they for? Any and all thoughts are welcome and appreciated.  ???

[dozerdan]

Hi
 I can tell that you are use to working on 4 stokes and not 2 strokes. One of the main differences in the 2 engine types is how the fuel and air finds it way into the cylinder.
 On the 4 stoke it just flow in through the intake valve. On the 2 stoke it flows through the intake port and enters the crankcase, not on top but underneath the piston. When the piston is on the downstoke,it opens up those 2 transfer ports that you asked about. Since the piston is on the way down and the crankcase is sealed, it pressurizes the case. This pressure push's the air and fuel up through those ports and it end up on top of the piston.
Later
Dan

[oldsaw-addict]

I actually am used to 2 cycle engines, but I havent seen many saws yet with the intake ports on the cylinder wall like this saw I have here, I dont have the same style engine on my PM610 but the 670 has it there.