Bob Paul wrote:
>Is there a formula to turn a physical gap opening into a 'dwell' ? Maybe
I'm
>just being real stupid about this, but....... The gap is published but I've
>never seen a report of the 'dwell' for a TR 3. Any help out there.
Actually, the gap setting is derived from the required dwell angle. For each
complete combustion cycle, ie. two revolutions of the crank, the distributer
rotor makes one revolution, or 360 deg.
For a four cylnder engine, each cylnder has a maximum of 90 deg distributer
rotation. During this 90 deg, the points must remain closed long enough to
allow the magnetic field to build up in the primary side of the coil, and
then open to allow the field to collapse, generating a high voltage discharge
from the secondary side. If the points don't stay closed long enough to build
the magnetic field, a weak spark will result. Too long, and the discharge
time is reduced.
Adjusting the timing sets the crankshaft angle (based on piston position in
the bore) at which the points open, and adjusting the point gap determines
the dwell angle. A smaller gap increases the time the points are closed, and
a larger gap the opposite. My Haynes Manual for an MGB gives dwell values of
60 +/- 3 deg, or 51 +/- 5 deg, depending on the model. These values should be
good starting points for the Triumph engines as well, I would think. In the
meantime, some TR3 owner will provide the exact values for a TR3, I'm sure.
Dan Masters
Alcoa, TN
'71 TR6 full restoration
'71 TR6 undergoing Ford 302V8 transplant
'74 MGBGT original
'68 MGBGT organ donor for the '74
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