Best way to measure Transfer opening?

[danders7]

Hi guys, I'm a total rookie when it comes to modifying a saw but I've been reading what I can and am trying to learn. How do you accurately measure when the transfer ports open? I've got my degree wheel mounted and the pointer set to TDC. I've tried sighting through the spark plug hole with a small flashlight but I have a hard time seeing with my old eyes where the bevel stops and the port begins.

I read somewhere about using a thin wire to stop the piston at the top of the port, and I tried that but the measurement has to fall short of the actual close of the port by the width of the wire. The question would be how far that is in degrees so I took a thicker wire and ran the piston up to the top of the transfer and recorded that point with both wire sizes. By dividing the difference in wire thickness by the difference in degrees I think I came up with how far the piston moves in inches for every degree of crankshaft rotation when the piston is at the top of the transfers. Does that make logical sense, or am I just overthinking the crap out of this?

 

[nmurph]

I don't know how thick the wire you are using is, but 1° is roughly .5mm.

 

[danders7]

I used wires that were .034 and .072 inches thick. The closing of the intake port measured close to your rule of thumb - my calculated travel is hampered by an inability to accurately read partial degrees rotation from a paper degree wheel on a CD so it doesn't make sense to try to do that when you can actually sight the piston through a port, but for the transfers that I can't really see very well I'll use the calculated opening. It was interesting that I was able to measure a notable difference in piston speed between the various ports. The intake moved 3 degrees between the thick wire and the thin, and the transfers moved 6.

I'm at 158 deg on the intake, 159 on the exhaust and 107 on the transfers right now. From what I've read I think I'd like that transfer number up to around 120, but I don't have a good way of raising the transfer ports so I'd have to lower the top of the piston to make the adjustment and I'm already concerned about how much compression I'm going to end up with. Maybe it wouldn't effect compression that much. I dunno though so it's going back together as is and we'll see how it runs.