Nolan Penney wrote:
>
> 10 seconds on, but how long off? It should be 15-30 minutes to allow
> a good cooling down. Now of course, none of us actually do that.
> We crank and crank and crank, hoping that the motor will act enough
> like a heat sink to allow us to get away with it. Often times you can,
> sometimes you cannot. Most starter motors will allow you to
> get away with upwards of a solid minute of cranking before
> self destructing in a terminal manner. But this does not mean
> that all starter motors will do this.
While it is an only slightly different situation for large diesels, the
same general rules apply. The starter we use is fairly lightweight for
heavy-duty diesel use, a Delco 41MT. This starter weighs approximately
85 lbs. The recommendations we make is to crank no more than 30 seconds,
and let the starter cool for at least two minutes before again trying to
start.
Even though the starting loads are obviously smaller for a Spitfire, so
is the starter, by a good measure. I would guess that after anything
longer than about five seconds of cranking, the starter should be
allowed to cool for two or three minutes. That may seem like not very
much cranking time, but count that out on the second-hand sometime, and
see how long it seems. An engine in good condition will start in about a
half-second, and perhaps 2-3 seconds in cold weather.
But, yes, one can appreciably reduce the life of a starter by
over-cranking. One large customer of ours had seen starter life go down
appreciably because their drivers were consistently over-cranking
starters in the winter, even though they were trained not to do it. When
they began to specify thermostatically-controlled starters (these have
an element which breaks brush power when the starter gets hot), the
problem went away, simply because the driver couldn't start the engine
until the starter cooled sufficiently.
Cheers.
--
Michael D. Porter
Roswell, NM
[mailto: mporter@zianet.com]
`70 GT6+ (being refurbished, slowly)
`71 GT6 Mk. III (organ donor)
`72 GT6 Mk. III (daily driver)
`64 TR4 (awaiting intensive care)
`80 TR7 (3.8 liter Buick-powered)
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