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MG MGB Technical - hot engine starter issue

My 1973 MGBGT will start fine when cold even after sitting for weeks. But after driving and letting it sit the starter just clicks and may are may not eventually work. I put in a new battery and also had the starter rebuilt by a reputiable shop.I have cleaned terminals. It seems to be some type of heat sink issue, the block heats up the starter and affects it.
bs stone

Does the 73 have an intergral solenoid? If its the seoerate one you can jam a big screwdriever across the terminals to see what happens! Just keep it clear of earth.
Stan Best

Your starter should be a pre-engaged type which means the solenoid is attached to the side of the starter. My guess is that the company that rebuilt the starter didn't replace the solenoid. The way it works is the solenoid first pulls a lever that engages the starter gear, once the gear is engaged the contacts within the solenoid apply power to the starter. It could be that gear (dog) is not moving freely, unlikely as this should have been checked on the rebuild, most likely is the contacts in the solenoid are the problem. The below link may be of interest
Bob Davis

i had/have the same issue. its very embarrassing when in a car park and you turn the key and all you get is a loud constant clicking noise. i replaced my starter with new which helped but when hot it still clicked about. i often had to leave the car to cool right down. after more inspection turned out the relay contacts by the fuses were very dirty. i cleaned them up and it was definately an improvement, but it isn't cured. it still does it occationally and so ill be keeping a lookout for a new starter relay.
Hope this helps
A P New

Thanks for your input.It does have a new external solenoid. I am surprised no one on this side of the pond has any suggestions.
bs stone

Seeing that you have replaced the solenoid I would suggest that you remove and clean all connections at the battery and starter end including the earthing strap. I would check the voltages at all points while trying to start You could have a cable that looks good be making poor connection inside the terminals themselves.
Probe check the battery post then the battery clamp and then stick the prob into the actual cable itself. do this at all ends and connections
You may be surprised to see the different voltages at thos points.

I had this problem many years ago with a VW. It turned out that the ignition was too far advanced. The car would start cold but when hot the compression was too great for the starter motor to overcome. Barrie E
B Egerton

Is it the starter clicking, or the relay? for how much the relay costs it would be worth replacing.
c cummins

V8 solenoids can definitely gradually fail whereby they need more and more current to operate them, but the symptom is that as the load of the starter is put on the battery the voltage falls, and if that falls below what is needed to hold in the solenoid then it will release, disconnecting the starter from the battery, so the voltage goes up again, the solenoid operates again and so on. Cleaning up my relay and solenoid connections did improve my chattering, but in the end I had to get a new starter.

I've not come across that happening to a relay but it's possible. If the starter still chatters when the relay brown and brown/white are connected together *reliably*, then the starter is still at fault, but it could also be a bad connection in the brown and brown/white going through the relay and down to the solenoid. If that's OK but it is the relay chattering, then it could equally be a bad connection anywhere in the brown - ignition switch - white/red - relay - black earth circuit as well as a faulty relay. I'd be measuring the voltages on all four relay wires and the terminal at the solenoid and comparing that with the battery voltage when the chattering happened. I hate buying stuff in the hope that it will cure a problem only to find it doesn't.
PaulH Solihull

If it's a bad connection or faulty solenoid or faulty relay. Why does it start when cold ? Barrie E
B Egerton

I'd agree with the above comments in that you need to measure the voltage at strategic points. Starters are fairly simple devices but because of the currents involved can be a pain tracking down the problem. I understand you've had the starter rebuilt but it's not impossible that's where the problem still lays. The company that rebuilt your starter will almost certainly only have tested it at ambient temperature, at which we know it works ok.

To understand what can cause a problem with starters you need to look at the figures. If we take some simple (but not unrealistic) figures, if the starter is trying to draw 100A and you have a connection somewhere in the circuit that has resistance of 0.05 ohms (to small for most cheap meters to measure), that connection will drop 5V across it, leaving only a nominal 7V for the starter. This could be either internal or external to the starter. If this were the case one give away would be the faulty connection would get hot, this wouldn't help if the problem is internal to the starter.

My suggestion would be unless you're proficient with a meter and vehicle electrics to take it to an auto electrician. Get the vehicle warmed up before you take it so that it'll fail and they should be able to diagnose it in a couple of minutes.

To answer Barrie's question, the problem is almost certainly caused by thermal expansion. This will cause the offending joint to expand and open up slightly. If the problem were in the starter the heat comes from the engine by heat soak. If it's elsewhere it comes from radiated heat from the engine.
Bob Davis

It gets worse when hot because physics dictates the resistance of the solenoid goes up which reduces the current. If the solenoid/relay is marginal or there is a bad connection and it's only *just* working when cold, it can easily *not* work when hot. BT, DT.

Ideally there should be less than half a volt dropped in all the connections between battery and starter motor when cranking. Even with only half a volt lost a good battery will lose another couple of volts internally, so you really never get more than 10v at the starter motor itself. I have seen 3v lost when there are bad connections in the main cranking circuit, but even though that results in only about 7 or 8v at the starter that should still be enough to operate the solenoid and relay reliably, the battery has to be pretty-well flat for the voltage to drop low enough to cause chatter - *if* everything else is OK. Get a faulty solenoid or relay, or bad connections around *those*, then you can get chatter even though you have good voltage at the starter.

You need to measure the cranking losses in the main battery circuit first, presumably when cold when it does crank OK. Disconnect the coil and put one meter probe on the 12v battery *post* (not the clamp) and the other probe on the battery cable stud on the solenoid. Crank, and measure the voltage. Then do the same between the battery earth post and the starter body. If you have twin 6v batteries then do the same again between the two battery posts the link cables are on. You may well need an analogue meter for this as the voltage will be wavering as the pistons approach and leave TDC on the compression stroke, digital meters can give average or unreadable results. Ideally each should be below half a volt, if any are over a volt then it is worth investigating further and cleaning connections carefully

Although I suppose you should measure between the battery posts first, to get an idea of the condition of the battery. However battery problems usually reveal themselves more during cold cranking than hot.

If all that is OK you can measure the voltages on the four relay spades, and the solenoid spade. The white/red, brown and brown/white on the relay, and the brown/white on the solenoid, should all be the same as the voltage on the solenoid stud during cranking, and the black on the relay should measure 0v. Any departure from this indicates a problem.
PaulH Solihull

Being over advanced will prevent hot starting. With the Bendix it doesnt crank, just throws it back out and you hear it whirr as it spins round. Not sure what a pre engaged does. Easily tested by retarding a few degrees. 100% agree rebuilt does not = good. Finding that out has cost me plenty over the years
Stan Best

This thread was discussed between 11/10/2010 and 15/10/2010

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