Last night when I put the cylinder back on, I used the degree wheel, first time. I got some readings but they don't mean much to me. They are as follows:
Exhaust start to open @ 93°
Full open @ 74°
Close @ 192°
Transfer and Boost ports are at the same level:
Start to open @ 118°
Full open @ 180°
Close @ 245°
As I said, they don't mean much to me, so if anyone could offer any help, that would be appreciated.
I think I stuffed up the exhaust close, I think that should be 267°
Based on your numbers, your exhaust port duration is 174 degrees, and your transfers are 124 degrees. The "full open" on both should be 180 degrees from top dead center, as that is half of the crankshaft's rotation. The closing value is not required - using some simple math (outlined below) you can sort all that out.
I'm quoting off-site here, forgive me:
Can someone explain me how to measure squish and port timings. I calculate the timings by measuring from the top on cylinder to the top end on the port, but doesn't seems to me that they are correct timings. Can someone explain how to measure with degree wheel. I have not got that one but I'll make it or order it. Please someone?
Thanks
Jon's suggestion on using the piece of solder crushed between the piston and head works great.
To use a degree wheel isn't too tricky.
Bolt the degree wheel to your crankshaft. You'll want to also bolt on some manner of pointer or indicator. I like to use a small piece of thick wire, as it's easy to mount and move around.
In the above photo, you'll notice the piston stop.
Rotate the piston clockwise until it hits the piston stop. Take note of the reading on the degree wheel (where the indicator is pointing). Then rotate it all the way counter-clockwise until the piston stops, and take note of that reading. You can then adjust the degree wheel (or the pointer) so that your readings are symmetrical. For instance, the piston stops at 9 degrees ATDC and 9 degrees BTDC:
9 degrees BTDC when the piston stops.
9 degrees ATDC when it stops in the opposite direction.
At this point, you have your degree wheel "dialed in", and it will provide you with accurate readings. Remove the piston stop and you can rotate the engine to 0 degrees which will be true top dead center.
Now, if you rotate the engine slowly and watch for the exhaust port to be opened by the piston. Sometimes it helps to shine a flashlight into the port so that you can see it easier. Take note of the measurement on the degree wheel. This measurement (let's just say 80 degrees after top dead center) is your port "timing". The duration is the span that the port stays open for, which is also measured in degrees. To determine your port duration after discovering the timing:
80 degrees is multiplied by two to get 160.
Subtract 160 from 360 to get 200. The duration of the port that opens at 80 degrees ATDC is 200 degrees.
It may sound complicated at first, but really it's not. You know that in a complete revolution, the crankshaft turns 360 degrees. From top dead center to the opening of the exhaust port, the piston travels 80 degrees. It's going to cover that same distance on the upstroke, which is why you multiply by two. Then, subtracting all of the rotation of the engine that does not involve the exhaust port will leave you with nothing but the the duration of the exhaust.
The transfers are measured the same way. Remember though, you will pass the 90 degree mark often when measuring transfer timing. After you pass 90 degrees, you need to pretend the degree wheel goes on past that, instead of counting back down, you count back up. After passing the 90 degree mark, the next one was 80 degrees, but you will need to count up instead of back down so even though it says 80 you need to think "100" The next after is 110 degrees and so forth.
I may not have done the best job explaining it. If I can explain something better, let me know and I'll do my best to help.
~Josh
Don't forget to use a piston stop when setting up your degree wheel. Otherwise your measurements will be off. When you go for the higher-end tuning, it's very important to get these things right.
Furthermore, don't forget that at some point in your measuring, you will pass the 90 degree mark on the degree wheel, and instead of counting down, you'll be counting back up (90, 100, 110 etc, instead of 90, 80, 70). It looks like you may have read back down when getting your "full open" value on the exhaust port.
Now, measuring the timings isn't the hard part... deciding where to go, and what to do with them are! It gets to be a bit much to explain at 11:00 at night (I'm usually in bed an hour ago), but if you haven't picked up a copy of A. Graham Bell's "Two-Stroke Performance Tuning", I highly suggest it.
~Josh
