At 04:15 PM 4/19/99 -0500, Perry Robinson wrote:
>>.... My A still won't turn over. .... with the spark plugs out, it spins
like a top, with them in, it won't even turn over one complete revolution.
>>....
>>The parts house where I got the starter retested it and says there is
nothing wrong with it.
I may have missed some of this, but do you have a good battery? A starter
can turn a free spinning engine without spark plugs with only about 30 amps
of current. With the plugs in and normal compression it will take 100-200
amps. If the battery is bad the voltage at the battery can go very low
with a high current draw. Low water level in the battery can cause the
same symptoms. Put a volt meter on the battery, directly on the battery
posts, not on the cable terminals. Try cranking the engine and see what
happens to the battery voltage. If it goes below 10 volts the battery is
bad (or may need to be recharged), or you may have a tremedously high
current draw from a short somewhere in the starting circuit.
And the starter needs to be tested while running under load. So, also
using a volt meter, put one test lead directly on the end of the power stud
on the starter motor, not on the nut or cable terminal. Put the other test
lead on the starter motor case, not on the engine block or chassis. Then
have someone crank it over while you watch the voltmeter. If you have at
least 9 volts across the starter motor while trying to crank and it still
doesn't turn the engine over, the starter is bad, take it back and get
another one and don't take any crap from the store manager.
If the voltage goes down to 5-8 volts while it barely turns, it may be
drawing an abnormally high current from an internal short. Ditto the prior
solution, take it back. Otherwise a common place for a short is where the
power stud passes through the end plate of the starter motor. It should
have a nylon bushing and bakelite washer here to isolate the stud from the
end plate. If the nylon bushing fails you get a short to ground.
If the voltage goes below 5 volts, then you probably have a bad connection
elsewhere in the high current circuit where you're losing the voltage. A
common problem is a missing ground strap between the engine and frame,
causing the starter current to flow through the choke cable or some other
high resistance path to ground. This short ground strap should be across
one of the engine mounts, or from a bellhousing bolt to the body or frame,
or from the rear cylinder head bolt to the body. There is hardly anywhere
else on the engine that it could reach a chassis grounding point.
Otherwise start checking sub-sections of the high current circuit with the
volt meter while trying to crank it to see where the voltage drop occurs.
Start with one test lead on the battery post and the other lead on the
cable terminal. If you see more than 1/4 volt here when cranking you need
to clean the cable terminal and battery post to get a better connection.
Do the same test for other connectors in the circuit: where the long
battery cable connects to the starter switch, where the starter switch
connects to the starter cable, where the starter cable connects to the
starter, where the grounding cable goes from the engine to the chassis,
where the battery earth cable connects to the chassis, and where the earth
cable connects to the battery. With two batteries you would also check the
connection(s) of the intermediate cable between the batteries.
When cranking, the starter motor should see at least 9 volts, and the
battery voltage should not drop below 10 volts. The loss of the remaining
volt or two should be equally shared amongst the 8 or 10 heavy cable
terminals in the circuit, not to exceed 1/4 volt loss at any one
connection. Voltage loss in the cables is nearly negligable, perhaps 0.02
volt per foot of length when carrying high current.
>>Does anyone know of a good reliable supplier of starters for the MGA? ....
Actually, no, I haven't had that experience. I've never killed a starter,
just had to repair a short at the input terminal occasionally. Starters
normally seem to last about forever, as they only run about 5 seconds for
each 50 miles that you drive. The most common cause of a burned out
starter is from someone cranking on it too long when it doesn't want to
start. Starter motors are designed for intermittent duty only, usually
specified as one minute use out of any 10 minute period (sometimes only 30
seconds out of 10 minutes). If you crank on it for a couple of minutes
straight there is a high probability of internal melt down.
And as this seems to be a rather persisent problem, the next question is,
where do you live? I have a perfectly good spare starter motor that I
could loan you for test, if it isn't too big an expense or hassle for
shipping. If all else fails, lemmeno. Uh, and don't the rest of you on
this list get any grabby ideas, 'cause I don't make a common practice of
loaning out parts of my car.
Regards,
Barney Gaylord
1958 MGA with an attitude
http://www.ntsource.com/~barneymg
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