1mm of timing????

[cchracer77]

Grew up in a world where we set timing in degrees, is the 1mm at the face of the flywheel or is it 1mm of piston travel, any idea how many degrees of advance that this is on a timing light?

 

[Jakobi]

Grew up in a world where we set timing in degrees, is the 1mm at the face of the flywheel or is it 1mm of piston travel, any idea how many degrees of advance that this is on a timing light?

Believe its 1mm on the face of the flywheel..

 

[cchracer77]

That seems how people describe it, but a quick eyeball would make that about 5- 10 degrees btdc, seems very small. My understanding of cdi's is that they retard it from this base setting, which would make the top possible 5 or 10 degrees?

 

[GMP]

mm refers to mm before top dead center, or BTDC. In the case of timing the GG, it just so happens that the 2K-3 stator plate is 353 mm across the mounting hole centers. What this means is that 1mm of plate rotation equals approx 1 deg timing change (353/360). To advance the timing on the 2K-3 you need to elongate the hole in the locating insert 1mm, or remove it.

 

[cchracer77]

mm refers to mm before top dead center, or BTDC. In the case of timing the GG, it just so happens that the 2K-3 stator plate is 353 mm across the mounting hole centers. What this means is that 1mm of plate rotation equals approx 1 deg timing change (353/360). To advance the timing on the 2K-3 you need to elongate the hole in the locating insert 1mm, or remove it.

If that is the case then the circumference would be 3.14 * 353mm = 1108mm / 360deg = 3.1mm/deg or 0.32deg/mm

 

[bergerhag]

If that is the case then the circumference would be 3.14 * 353mm = 1108mm / 360deg = 3.1mm/deg or 0.32deg/mm

The math is correct but is it reasonable? This calc would assume the engine is sportin a 10 inch flywheel. Or 0.3 m. No, the 353 mm is a circle drawn through the centers of the stator mounting screws. The math is already done.

 

[Jakobi]

As Glen said.. 353/360

0.98mm per degree

 

[pscook]

I believe the circumference is 353 mm, which drives a 112.42 mm diameter flywheel. 353 mm diameter flywheel would be almost 14" across. The 112.42 diameter number is probably more accurate as that is 4.43" (I'm American. I can't do visual approximations in metric over 25 mm).

 

[cchracer77]

If that is the case then the circumference would be 3.14 * 353mm = 1108mm / 360deg = 3.1mm/deg or 0.32deg/mm

Was jesting at the apparent confusion between diameter across and circumference around, but that neither here nor there. I am trying to establish timing marks to verify that it is accurate, not just blindly advance it a few degrees.

 

[GMP]

Sorry guys I worded that poorly. Its approx 353mm circumference, THROUGH the hole centers, not across. Close enough that you can use the edge of the stator plate and case for reference marks.

 

[Leo]

This relation between mm before top dead center and rotation degrees in flywheel change with the connecting rod angle. So, this is not an good method. To do the movie below, i see that near TDC this relationship change very quick. Try to use one kind of scale thru the spark plug hole at least to check if the degrees math/measurement is ok.

http://youtu.be/XkJQsVgMTLE