I'm sorry but these specifications make no sense, and are not supported by
any literature I have read in the automotive field over the last 40+ years.
A 2 volt drop in a starter circuit is huge. A 2 volt drop is border line no
start on any car. The industry specification is 0.3V for the positive cable
and 0.2V for the negative cable. Note some sources say 0.2V for both
cables. Remember we are talking about the voltage drop or difference in
potential between the battery end of the cable and the starter end of the
cable, so we are discussing just what is being lost in the cable and
connections, not the draw down by the starter.
Torque at 1,000 RPM? Starters turn the engine at 200-300 RPM period. Don't
believe me? go out to your Healey, crank it and look at the tach. It is not
showing 1,000 RPM 15.5 foot lbs of torque from the starter? I have no clue
what this is supposed to be or how you are going to verify it. Talk about a
useless number.
570Amp draw on the starter as normal? No way, no how. Normal amp draw on a
gas engine starter is in the 100-150 amp range. I would expect a Healey to
draw in the neighborhood of 125 amps or so. Most batteries won't deliver
570 Amp for more than a few seconds. For a comparison a high compression
big block Chevy motor with a bad starter will draw 300 Amps and barely turn
the engine over. Also a 300Amp draw the battery cables get hot from the
amount of current.
Locked up torque? No idea what it is, but 900A draw? You will melt the
cables. This is basically a dead short across the battery terminals. You
are discussing major league arc-welding here. 900A at 12 Volts is about
14.5 Horsepower.
Likewise a 115Amp hour battery? I don't think so. Gas engine cars
typically have a 30-45 Amp hour battery. The replacement battery that Moss
sells for a big Healey is a Westco and is rated at 31 amp hours. sounds
about right based on my experience. A diesel Mercedes has a fricking HUGE
battery, it is rated at 88 amp hours, and you are telling me the Healey had
a battery almost 50% larger than that? Nope, not buying it.
Rick
On Mon, Aug 8, 2011 at 12:46 PM, John Harper <ah at jharper.demon.co.uk> wrote:
>
> Joel
>
> A larger diameter cable will do no harm and perhaps give the starter a
> little more 'sparkle' but the original cable to the correct specification
> with good terminations is quite adequate.
>
> 2 volts drop is not that great. Bear in mind that the official test
> specification for 'our' M45G starter is
>
> Torque at 1000 r.p.m.: 15.5 lb.ft with 570 amp at 8.8 terminal voltage
>
> Lock Torque 32.5 lb.-ft with 900 amps 6.4 terminal voltage.
>
> This with fully charged 115 amp.hr battery at 10-hour rate.
>
> So taking the first 1000 r.p.m. as being a typical starting figure we have
> about 4 volts drop and this with short test leads used on the rig and a good
> high capacity battery.
>
> It is more likely that your battery has an increased internal resistance
> due to age etc.
>
> Before changing anything else I would try an alternative battery.
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