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MG MGA - Strange Electrical Problem

Hi Folks. My friend Terry recently completed a ground up restoration on his MGA 1600 roadster. The car runs great, and all the electrical components (such as lights, signals, horn, wipers, starter, work perfectly. EXCEPT when the car sits unused for a week or so. After sitting for a week or so, the car cranks very, very slowly. BUT, after pulling the starter button numerous times, and having slow cranking on those occasions, the cranking speed eventually INCREASES to very near normal cranking speed!!! It is as though the almost dead battery gets better after cranking the engine several times. I have checked the battery terminals and posts, and they are clean and tight. I have checked the ground strap on the engine mount, and it is clean and tight. I have also checked the battery cells with a hydrometer, and they are all reading as very good. The starter and generator are freshly rebuilt, I have retested them, and they are both working fine. Before the car is stored, the battery cutoff switch is engaged, making battery drain from the car's electrical system essentially impossible. After the car is driven for a while, and shut off, it immediately restarts at normal cranking speed, and does so until the car is stored for a week or so, and then it cranks slowly again. This is an unusual situation to say the least! Has anyone run into this situation before? Does anyone have any idea what could be wrong? Personally, I think the battery might be internally defective, and intend to try swapping out the battery, with a different one. Thanks! Glenn
Glenn

I have seen this before (as recently as last week). The cutoff switch is the culprit. It has a resistance, which reduces as it gets warm from the current passing through the contacts. Try bridging the contacts to bypass the switch, and I think you will find that's where the problem is.

If the MGA is properly wired, there is nothing that can cause a drain on the battery if the ignition is off, so the isolator switch is not required (even as a security device - I find that the unusual handbrake is enough to confuse anyone!)
dominic clancy

Glenn:

An alternative to the electrical fault line of thinking...

You state in your post that the car was recently rebuilt from the ground up. Assuming that the engine was rebuilt at the same time and that this problem was present from the first time it was started after the rebuild, is it possible that the starting problem your friend is experiencing is due to internal engine binding - such as from the crank journals being slightly misground? A check would be to remove the plugs and see if the engine can be turned by hand easily with the crank (or a wrench/spanner on a engine with no ears on the crank bolt). After the car warms up and the oil thins out, it would start up more easiliy.

Steve
Steve Brandt

Glenn, Is it safe to assume that since it was a ground up restoration, that the battery is new?
I would take it to a place that can test it and see what it shows, sounds as if it might have a high internal resistance.
good luck/ gil
gil

Two things.

I cut the brown wire that goes to the starter solenoid on my car and installed a spade terminal and plug thing on the solenoid.
So when it is not being used I can disconnect all the electrics. also if your working on the car you can unplug it...

Also I replaced the Solenoid, as mine would start OK one min and the next crank very slowly. Problem solved when I did.

Hope this helps
<MARK>
Mark Hester

If you have a voltmeter, you could check the battery voltage right on the battery posts during cranking. This would tell you if the problem is with the battery.

I know you have checked all the connections and they look good, but looks can be deceiving when it comes to connections. I would still suspect a poor connection somewhere in the starter circuit. New cabling can have bad crimp connections, or possibly the starter switch or the cutoff switch are developing slight corrosion after sitting. If it is cranking slowly because of a weak connection, that point will most likely be getting hot. When it is cranking slowly, feel all along the heavy wiring between the battery and the starter including the cutoff and starter switches, and all the ground connections.
Jeff Schultz

Mark, In standard form, the disconnecting of the brown wire for storage is unnecessary. If the generator control box is functioning properly, (see post about a week ago) there is no current draw while sitting parked. All that changes the minute one upgrades the car such as adding a radio clock or other electronic devices (solid state SU fuel pump or ignition?). I routinely store my car for 5 months at a time without disconnecting anything except the radio/CD Player.

In hot environments, the self-discharge rate of the battery will leave you with not enough to start the car. But that would occur with or without the brown wire disconnected as it is internal to the battery.

Glenn, Are you trying to start the car with the clutch depressed? Does the slow cranking go away when left in neutral and the clutch pedal untouched? Possibly could be the thrust bearing being a bit dry and needs the oil to circulate a bit. This would explain a cranking speec that slowly increased as you cranked. I always start my car with the trans in neutral and the clutch untouched.

If the cranking stayed consistently slow then all of a sudden started cranking fast, I'd do a voltage drop measurement across the starter switch while cranking. More likely this is the culprit.

Chuck
Chuck Schaefer

Hi all. Thanks for the useful tidbits of information. I will investigate the problem further in the next week or two, and will post what I discover. Cheers! Glenn PS The battery is brand new, the engine turns over nicely with the hand crank, I have tried starting both with and without the clutch pedal depressed, and I have jumpered (bypassed) the starter switch. The problem remains.
Glenn

This thread was discussed on 04/10/2005

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