Hi Mike

I looked in the Yellow page and found an auto electrician. They had a test rig and confirmed its servicability.

Charged me a fiver for that and testing my alternator.

Should be one in your area.

Pete

Hi Mike.

Peter's advice sounds sensible!

However, if you are into sussing out your own problems, you could try following the hefty red cable from the starter motor and see where it goes. If it goes straight to the +ve of the battery, then the starter relay is built into your starter motor assembly.

If, however, the cable goes to a small unit before continuing (from a separate terminal on the unit) to the battery, then THIS is the relay. Check the tightness and cleanliness of the terminals on this unit, and it should make a definite 'clunk' when you turn the key to 'crank'. You can also do a by-pass test on this relay (ooh, look at the sparks!!) by bridging the two heavy terminals with a HEFTY piece of metal - say, a spanner. It WILL spark quite dramatically, and will leave scorch marks on you tool (ooh-er, missus) - try and press it on firmly for a couple of seconds (and make sure the car ain't in gear...)

If this causes the starter motor to turn, then you can safely consider the problem to lie with the relay or its wiring. As well as the two heavy-duty terminals on the relay, there should be a separate thinner wire. This is the 'trigger' wire from the key switch. If you take a 'live' from the battery +ve, and touch it on this terminal, this should cause the relay to energise and the starter motor to turn. (If there are more wires than this on the relay, make sure you know which one you are working with!

If the relay is built-in to the starter motor assembly, you can try the same trick of taking a 'live' from the battery and touching it on the 'trigger' terminal on the starter motor, ie: the thinner wire terminal. If this makes it work, it would appear that the problem lies with the feed from the key switch.

MAKE SURE YOU ARE COMFY WITH WHAT YOU ARE DOING BEFORE YOU DO IT!

(I've no experience of the MG's starter - the above is based on Ford stuff, but should be similar!)

My donor is a '69 GT and I don't recall a separate relay on it when I dismantled it. So the relay is probably going to be built into the starter.

All

Many thanks for your comments and tips gentlemen, I'll give them a 'go' this weekend.

1. The lighter wire travels from the small starter motor terminal to a small relay under the dash.
2. There are 2 types of MGB GT starter motor, mine is the pre-engage type (2 units strapped together).

Regards
Mike

Hi Mike.

In that case, the 'relay' will be built-in to the starter motor assy. I understand what happens is that a solenoid (the extra bit that's attached to the side of the motor) fires the pinion forward to engage with the flywheel and at the same time the solenoid lever bridges the heavy-duty contacts which delivers the large current to the motor itself. The starter motor drive pinion is therefore engaged with the toothed ring on the flywheel before the starter begins to turn.

The thinner wire is the triggering wire from the key switch. The relay you found near the dash is there since the solenoid itself needs quite a few amps to power it, and the key switch (or push switch?) would find it hard to handle this current directly.

(This relay is, however, quite different to the relay we were talking about earlier! This earlier relay (or the solenoid contacts you seem to have) has to handle literally 100's of amps to supply the starter motor. You DON'T have this separate relay - it's all part of your starter assy.)

Based on what you say, I think my testing procedure would be something like:
(a) check that all the terminals on the starter motor are making good contact (but I guess you've done this anyway since you had the motor off?)

(b) take a live feed from the battery and touch it on the smaller contact on the motor and see what happens! This will tell you if the motor assy itself is working ok (assuming the thick supply cable and battery connection is fine, of course)

(c) remove the thinner wire from the starter motor and connect it to a 12V lamp, with the other end of the lamp going to a good earth - turn the key to 'crank' (or push your button!) and see if it lights up. This will tell you if the key switch and small relay is working ok.

Based on the results of the above, you should know roughly where the fault lies!

Donnie

Many thanks for the tips. I will try them this weekend.

I checked with MGBhive this morning and they have pre-engage starter motors in stock (£75). I just wanted to be absolutely sure that it was the motor.

The motor has been failing to run over the last couple of months or so but only after I have driven some distance and parked. I'd get out turn the fuses around, waggle a few wires and it would turn over.

I had to have a push start last Sunday to get us home. I must put a stop to that!

Regards
Mike

Ha ha! You certainly don't want to have the same problem after fitting a new starter!

If the motor tended to start working again after a bit of jiggling of the wires, it would suggest loose connections rather than a faulty motor (yeah, I know - eggs, Granny, and suck...)

Dodgy connections do tend to become worse over time, so it's not too surprising if it's completely kaput at the moment.

You can also separately bench-test the starter motor if you wish: first clamp/tie it down firmly using, say, a 'workmate' or similar. You'll need jump-leads for the heavy-duty supplies, and then simply take a +ve link to the smaller terminal. It should burst into life quite dramatically - a loud 'clunk' as the solenoid fires the pinion forward, followed immediately by a crisp and powerful spinning of the motor; there shouldn't be any laziness or slow build-up of speed - it should all be pretty immediate.

The large connections on the motor really do need to be in good order as they carry huge currents. Any resistance due to loose/dirty connections will cause problems due to this current - it'll create heat and make the connection worse.

Check not only that the cables themselves are bolted down tight on the terminals, but also that the terminals themselves are secure and look clean - no signs of over-heating, etc.

Enjoy!

Donnie

I am going to have fun this weekend. The bench test method is going to be very convenient. The Motor is all 'cleaned up' and sitting on the bench and I have a power pack with heavy duty leads.

Regards
Mike

Hi Mike.

By 'powerpack' do you mean an electric starter booster? I guess this will do the job, but bear in mind that a starter motor will draw (and require) a couple of 100 amps to run properly, and if your unit won't deliver this, it might give you a false idea of the motor's performance. Eg, a normal battery charger won't even begin to move the motor!

The simplest thing to use is a fully-charged battery and jump leads (but keep the ends well apart!)

Good luck.

Donnie

The Power Pack is a powerfull portable battery as sold in Halfords etc. It has delivered sufficient power to start the car in the past.

Pproblem has been solved by replacing the fat bodied Starter motor with a new slimmer version. One of the terminals on the old motor was broken inside the pre-engage solenoid.

I still have an issue with electrics after the engine has been running for a while. But this is a seperate issue and am working my way through the loom to discover what's causing it. A wildly fluctuating Fuel gauge has my full attention at the moment.

Again many thanks for the information.

Regards
Mike

Hi Mike.

Very pleased to hear it's sorted. It's also good to know the actual cause has been found - nothing worse than 'fixing' something, and not knowing what the problem was in the first place...

There's a thread below started by 'Ned' concerning a 'fuel gauge' problem - erratic reading. Can't add much to it!