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MG MGA - My Ignition Mechanical Advance - Again

Those of you who followed my recent thread will remember that I had problems getting my DM2 mechanical advance set up right in my 1800 engine. The distributor came back from the rebuilders supposedly reprofiled for the 1800, but it never worked well. I found it had an incorrect (7 degree) cam arm. Something in the region of 12-15 degrees would have been more like it. I eventually got it sorted and have been driving the car for the last 2 to 3 weeks.

However, during this time I have increasingly felt that acceleration up to 2500RPM is not as good as it should be, although the car performs very well at higher RPMs.

So, I have today refitted my 45D distributor (with an Aldon (pertronix) electronic ignition). The car instantly felt right. I plotted the advance curve and you can see on the attached image how the 2 distributor curves compare.

My analysis is that the primary spring in the DM2 is too strong or the bob weights are not heavy enough, giving insufficient advance at the lower RPM range.

The attached diagram assumes 8 degrees static. So, for example, at 32 degrees crank advance at 3500 RPM I have subtracted the 8 degrees and divided the resulting figure by 2 = 12 degrees of distributor advance.

Any comments?

Steve


Steve Gyles

Steve,

What are the cam arms stamped with (degrees) in your old Metro 45D distributor?

Regards...John
J Bray

John

15 Degrees.

Steve
Steve Gyles

This thread was discussed on 23/02/2008

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