- Thu Jun 07, 2012 6:22 pm
#13281
Hi Howzie. The Auto advance unit (AAU) will advance the timing by about 20-25 degrees. The figure is usually stamped on the back of the rear plate of the unit and is shown as the actual points-cam movement in degrees (10 or 12 degrees) so you double the number to get the actual crankshaft advance figure. What really only matters is the timing at full advance and with a mechanical device it usually at around 2000-3000 rpm but the exact figure depends on the strength of the springs fitted. If the AAU is the original type that is correct for the engine, it will be provide the correct timing at the correct rev range. So all you have to do is check with the strobe that when you rev the engine the full advance position shown by the strobe marks is just reached and increasing the revs higher must not produce any further advance in the timing. What ever the revs are when this occurs will be set by the AAU and as long as the timing mark appears to lock out at the correct position, everything will be correct at lower revs. Of course the springs could be very weak, and the max advance will occur at lower revs, but what is more important is that the maximum advance timing will not be exceeded no matter what higher revs you go to as the bob weights simply come to the end of their movement range and cannot move any further. Slight variation of the advance range at lower revs can only be dome by comparison to a known perfect/new AAU. Rest assured though that the springs are never stretched that much in use and the amount of weakening over a life time is very small. New and stronger springs are available should you wish to renew them.
