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MG MGB Technical - How to test a starter?

Does anyone know how to test a starter using the car's batter etc.

I am having issues with starters and I have already replaced two since the Summer and the last one died on me yesterday, having only been installed for a week and a half :-(

When I remove it I just want to test it to make sure that its the starter and nothing else before I go and buy a new one. One came out of my parts car and the other, which just dued came from a car show, which bench tested fine.
GG Ginty

GG - You don't say what year your car is, which would make a big difference in troubleshooting the problem. In an early car the problem could well be the the external solenoid rather than the starter itself or the drive gear/ring gear that is causing the problem. In a later car, there is less change of the drive gear/ring gear causing problems and the solenoid is part of the starter assembly, but there is a starter relay that could be causing the problem. Before replacing another starter, I would suggest taking the suspect starter to an auto electric shop (a real one, not the bench at the back of Auto Zone or other such discount store) and have the test the starter after explaining what you have been experiencing. Cheers - Dave
David DuBois

From your later post you say that your car is a'74. As Dave said, the best way to test it is to have it done on a test bech at a shop. However, you can mount it in a vise, run jumper cables from a battery to the starter and get a basic test accomplished. Ground the starter to the negative terminal of the battery, run the positive cable from the battery to the the large post on the rear of the solonoid. Nent, jump the connections from the large post of the solonoid to the smaller solonoid post. There may be 2 small spade connectors on the solonoid, one for an ignition boost and the other to activate the solonoid and starter. If one of the jumped connections does nothing than try connecting the other spade terminal to the large post on the solonoid. It should cause the starter to run at a very good speed. Failing this test, the starter should come apart for inspection. RAY
rjm RAY

It doesn't need cables you would use for jump starting for doing a simple go no go test on the bench, any couple of wires will do. The starter only takes a very high current when it is turning the engine over, not when it is spinning freely. Thinner wires are easier to wrestle with and will cause less of a problem if they happen to short together.

Only a rubber bumper starter would normally have the second solenoid terminal, but of course one picked up from a show or whatever could have either, and it is moe of a problem if a starter for a rubber bumper car *doesn't* have the 2nd spade.

Your ears are a good test of what might be wrong. On a car with a starter relay i.e. 70 on the relay should make an audible click as the ignition key is turned to crank, less easy to hear on a LHD perhaps but still should be possible. Ordinarily that will be drowned out by a louder clonk from the solenoid, and again ordinarily that will be drowned out but the grinding of the motor. So the important question is, if it didn't turn the engine over, did you hear a clonk? A click? Or nothing at all?

If you heard a clonk then the problem is definitely in the starter, either dirty contacts in the solenoid, or in the link cable to the motor, or bad brushes or windings in the motor.

If you heard the relay click but no clonk then the problem is either bad relay contacts, no 12v supply on the brown to the relay, a bad connection in the white/brown from relay to solenoid, or the solenoid winding open-circuit.

If no sound at all then the problem is either in the ignition switch, the white/red wiring to the relay, the relay winding, or there is no earth on the black to the relay, i.e. nothing to do with the starter at all.

It's quite possible that changing the starter jiggled some bad connection elsewhere so initially the replacement starter worked, but the bad connection has reared its ugly head again. This is why you should always do a full diagnosis before diving in and spending money. Or the original starter was faulty but something else has gone wrong now, or the other way round. Or both starters are indeed faulty, which is a problem with new stuff let alone 2nd-hand.
Paul Hunt

Paul,


I am pretty sure that there is a define clonk when you turn the key. I may just have to break down and buy a new one. The one I put in earlier came out of my 77 parts car. The car had been standing since the late 90's and started to show symptoms soon after, didn;t sound strong after about a month and it took me a while in the morning to fire up. Once it fired up I had no issues at all durnig the day until the following morning. It finally gave up with just one loud clonk when the ignition was turned. I replaced ths a week and a half ago with the current one, which was second hand. The first time I fired the car up with this starter, as soon as the car fired up there was this loud squeek/whizzing noise which would go off as soon as the starter disengaged and lasted no more than a split second.


Gerry
GG Ginty

I think most auto parts places will bench test it for little or no fee.
Patrick Callan

The load squeak/whizzing noise will be the engine spinning the starter, as it isn't disengaged until you realese the key unlike the earlier inertia starters that throw the pinion out of engagement as soon as the flywheel turns faster than the starter. A whzzing noise would be normal, a loud squeak less so :o)
Paul Hunt

Before you buy a new starter, look into rebuilding the one(s) you have. I've worked on marine outboards and had several MGs over the years. I never had to buy a new starter. You should be able to find a good auto electric shop in the yellow pages to test it and rebuild it. Thus, you maintain the correct, original starter.
Rick Penland

I had a failing starter where you could hear the solenoid clonk but sometimes the starter wouldn't fire. It turned out to be very worn out solenoid contacts. I just bought a new solenoid (a very nicely made Japanese unit) and that sorted it out. I do remember a long time ago bench testing the starter with a battery and some wires just to make sure the starter gear would move out and engage properly and then the starter would spin.
Simon Jansen

Testing questionable starters with skinny wires on the bench in your home garage or haveing it tested by 'Billy" at the local Auto Zone will give you a little info and only a little. A good rebuilding shop can test the starter under load seperateing it from the rest of the car, so if it works on the test bench and not in the car you know you have to test the rest of the car not the starter. Finding a local rebuilder
that you can get to know and form a close relationship with, is worthwhile. A true pro will have knowledge and equipment that most of us don't have the time or money to obtain. Keep us informed. RIC
RIC LLOYD

To be fair I did say using skinny wires was only for a simple go/no-go test and is something you definitely want to do before fitting aa replacement to the car and finding out it is a no-go! Rebuilders in the UK at least are few and far between, probably only deal with retail suppliers, and won't be geared-up for some bloke turning up with a mucky unit in his hand asking if it is any good.
Paul Hunt

Paul no disrespect, but I have found that people sometimes take even the best instructions out of context. The point I was makeing was that there are tests that can be made by pros that give good info that are hard to duplicate for the hobbiest. I can't speak to the number of rebuilders in your area, but I can say that they are out there,often they are small,three or four people, and if you get to know them they are willing to help.
"Test twice, install once" Ric
RIC LLOYD

This thread was discussed between 01/11/2009 and 19/11/2009

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