Friday, September 16, 2011

Timing settings

I've been looking at what to use for crank timing settings.  There's a difference in the 60-2 timing wheels between the non-VANOS M20 & M50 and the VANOS M50, M52, S50, S52 & S54.  For some reason, the S54 was put back into the non-VANOS camp.

The notch in the wheel is offset by 120 degrees between the two. 

Megasquirt 3 needs to know the degrees of rotation from the #1 tooth BTDC to the point where the motor is at TDC.  The #1 tooth is the first tooth that the sensor sees after the long gap.  The angle is measured by counting the gaps between the teeth and multiplying by 6.  There are 14 gaps between the tooth at TDC and tooth #1 on the M20 wheel, 14x6=84.

The bottom line is that for non-VANOS motors the number is 84 degrees BTDC and for VANOS it's 324 degrees.

A comparison of the two types of BMW DOHC timing wheel
Also of interest, the internal crank-mounted wheels on the M52, S52 and M54 have the same timing as the ones pictured.

There is a 1 1/2 degree difference between Hall sensors and VR sensors; a Hall sensor reads the edge of a tooth while a VR sensor reads the middle of a tooth.  I don't think it makes a difference since tooth #1 is read the same as the TDC tooth.

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