Scott,
Sounds mostly like a dying, or now dead, alternator - although I admit it is
strange that Hobbs started up right up after driving for bit, which is usually
a sign of a dead battery - battery charges while you are driving, is fully
charged once you have stopped, but loses its charge over time (usually
over-night). When you say that he is starting up without problems now, is
that even after sitting over-night?
I would do a little voltmeter diagnosis. With the car having sat over-night or
longer, check the voltage at the battery - should be 11.5-12V, any lower and
you have a dud battery. If possible, get someone else to turn the engine over
while you continue to check voltage - it should drop to around 7-8V (I think)
while the starter motor is cranking. Any lower, or if the starter motor is
cranking weakly or not at all, you have either a dead battery, or the battery
is simply flat because it is not being charged.
With the engine running, check the voltage again. Should be 14-14.5V (with the
engine running a bit over idle, say 1000rpm+), any lower and your alternator
is dying (if voltage is above 12V) or dead (if voltage is 12V or lower).
In the UK at least, new batteries are about 25 quid ($38), and re-con
(exchange) alternators are 30 quid ($45), and, surprisingly, I have found not
only batteries but also alternators at my local car parts dealer, and cheaper
than the Triumph specialists. Not a huge amount of money to worry about.
Hitting the starter motor only works on solonoid-engaged starters. These use
an electical coil to move a magnet, which pushes the pinion along the starter
motor shaft so it engages with the flywheel. As the pinion engages, the
solonoid also completes the electrical circuit so the starter motor will turn.
Sometimes the solonoid does not move quite far enough to complete the
electrical circuit, but hitting it jogs it so it moves a bit further and the
circuit is completed, and the motor turns.
The Spitfire starter works a little differently. There is still a solonoid,
but it is remote from the starter (sits on the bulkhead next to the coil).
This has just one function, to complete the electrical circuit - it is
essentially a big relay. The starter motor pinion engages with the flywheel
because it sits on a worm gear on the motor shaft - as the motor suddenly
starts spinning, the inertia of the pinion means that it would prefer not to
spin, so the worm gear makes it shoot along the shaft instead, until it
engages with the flywheel. Conversely, once the engine starts it will try to
drive the pinion faster than the starter motor, and this drives the pinion
back along the shaft until it disengages - this is why the starter motor on
Spitfires disengages if the engine fires once but does not run.
With a flat battery, you often get a loud 'clunk' when you turn the key for the
first time - the solonoid has completed the circuit, the motor has started to
spin so the pinion has engaged with the flywheel, but all then stops because
the motor does not have the strength to turn the engine. Next attempt you get
a quieter 'click', which is the noise of the soloniod completing the circuit,
but this time the starter motor doesn't even try to turn.
Hope this helps, keep us all posted!
Richard & Daffy
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