[Healeys] Dwell angle for standard BN1 100/4

David Porter frogeye at porterscustom.com
Fri Oct 24 07:07:07 MDT 2014


oh geeze.. hope this doesn't turn into a 'what oil' or 'what tires' 
thing.. anyway it has made me think and start reading (easy with 
computers these days). problem is separating machinist think from 
mechanic think, I think. ;~)
  Any way here is a short explanation for all of us directly from the 
Internet I found this morning:

When the distributor shaft is rotating, the contact-breaker points open 
as the heel of the moving point is pushed outwards by a lobe of the cam, 
and close while it is over the flat area between two lobes.

If, for example, the angle of rotation between the centres of the lobes 
on the cam is 90 degrees, the dwell angle - the period with the arm over 
the flats and the points closed - may be 52 degrees; the remaining 38 
degrees are taken up by the action of opening and closing. This would be 
a typical dwell angle for a four-cylinder engine 
<http://www.howacarworks.com/basics/the-engine>.

A dwell meter connected between the distributor or ignition coil and 
earth registers the dwell angle on a scale, and must remain steady at 
the prescribed figure while the engine is running. If the dwell angle is 
not the same for all cylinders, the result is rough running and poor 
fuel economy because the moment the spark-plug fires varies from 
cylinder to cylinder.

The dwell angle varies according to the make of car; check it in a 
service manual. There are two scales on the meter, one for four-cylinder 
engines and one for six-cylinder engines. Eight-cylinder vehicles are 
taken from the four-cylinder scale and halved.

  End of article... I liked this one best as they use the numbers I 
posted yesterday that let me validate (personally) that I haven't 
completely lost my mind yet..:-)
   BTY, I don't ever disagree with Michael or Richard, Kees sometimes..
dp


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