intermittent slow turnover

[David Ambrose]

Hi, i am currently trying to restore a 1967 Mk1 MGB GT which is giving me a few issues with starting.
it seems to have an intermittent fault where it sometimes seems like it's pulling to much power and acts like the battery is week, i know it's not the battery as i have tied multiple batteries and also via jump leads from a running car.

I have replaced both the earth lead from the battery to the chassis and the chassis to the engine. i also tried disconnecting the dynamos invade that was causing an issue.

this is only intermittent as approx 2 our of 5 times it will turn over as expected and start up.

Any ideas would be greatly appreciated.

Thanks

[Peter Cresswell]

Hi David,
I have encountered something similar many years ago with a MK1 Escort RS2000. It displayed all the symptoms of a flat battery, and if the battery was put on charge, for a while it started fine. I even replaced the battery which initially enabled it to start easily but after a few days the problem reoccurred. Eventually I took the starter motor out and took it apart. The field coils, which are attached to the case had a braided lead to earth them to the case and this had frayed over time. I drilled through the flat part of the wiring just before the braid started and also through the case with a suitable size for a small brass BA bolt and nut to earth the coils. The problem never occurred again. A very cheap fix!
Before you dismantle the starter though, have you tried changing the starter solenoid? You mention the car is undergoing restoration, so presumably it has been unused for periods of time. I think your car (1967) will have the Bendix type of engagement and a separate solenoid mounted on the offside front wing. These are cheap to buy so it might be worth trying a new one to see if that cures the problem. I suppose there is a chance that the starter has been changed to the pre-engaged type where the solenoid is mounted on the underside the starter motor. In this location it gets all the muck and spray off the road hitting it and often the terminals are not in good condition, especially after 50 years. Access is only from under the car, and it will be easier to take the starter motor out so you can see what you are doing. The solenoid is available separately but is a bit more expensive than the remotely mounted types. I don’t think you can change the Bendix type starter for the pre-engaged type without changing the engine backplate, and if your car is the Bendix type, you will need a spring compressor to remove the pinion.

I hope you have checked the main battery feed from the battery to the front of the car, as this very vulnerable to damage underneath the car.

So check all the wiring first, then the solenoid and replace is necessary, then if you want to strip down the starter motor to check the earthing of the field coils do so, or replace the starter motor.
Don't forget to disconnect the main lead on the battery before working on the starter motor or the solenoid. It can carry several hundreds of amps in a short circuit, and although it may not kill you it will shower you with a lot of molten metal!!!!