Morris Oxford - Morris Oxford

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Sat 10 May 2014 08:22
Morris Oxford - Morris Oxford - Moggy1950

I have a 1950 Morris Oxford. The coil heats up after running her for a while...I've put a new coil on but it's heating up as well. What would cause the coil to heat up? The car stalls and stops when the coil gets very hot. Thanks

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Sat 10 May 2014 09:02
Morris Oxford - Morris Oxford - gordonbennet

Blimey, racking the old grey matter now..;)

They do tend to get hot, oil filled to help keep the heat down.

Coil connected the right way round, bearing in mind that many positive earth (if it was) dynamos were flashed over to neg earth, can't remember if the coil needed reconnecting, might be worth checking.

Other than that, possible condensor breaking down or some other fault, with points unless you're running the new fangled electronic ignition, the coil may not be the base problem, obviously you've checked spark plugs and leads, and all LT wiring, oh and fuel pump and is there any oil in the carb piston damper, SU or Stromberg...did Stromberg have a piston diaphragm?

Have you substituted the other coil when the car stalls, does that immediately cure the problem until that one heats up?

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Sat 10 May 2014 09:23
Morris Oxford - Morris Oxford - skidpan

Have you fitted a coil intended for a ballasted ignition on a car that was never wired for a ballasted coil. A ballasted coil normally runs at about 9 volts through a ballast which is bypassed to give 12 volts initially on start up to aid starting. If you run a ballasted coil on a non ballasted system it will receive 12 volts all the time, something it cannot cope with.

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Sat 10 May 2014 09:44
Morris Oxford - Morris Oxford - Railroad.
There are basically three types of ignition coil and it is important that you have the correct one for your car otherwise you will have problem. Remove the two small wires from the coil, and check its resistance using an ohmmeter.

1. 12v standard coil. For use with basic 12v systems with points and condenser. Primary resistance around 3 ohms.

2. 12v ballast. For use with 12v systems with points and condenser, and fitted with a ballast resistor. Primary resistance around 1 - 1.5 ohms.

3. Electronic. For use with electronic ignition systems. Primary resistance less than 1 ohm.

Unless your car has been modified it will most likely have a 12v basic system. Fitting one of the other two coils will seriously reduce the life of the contact breaker points and cause the coil to get hot.
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Sat 10 May 2014 12:33
Morris Oxford - Morris Oxford - Peter.N.

I would agree with the above, its likely you have the wrong coil fitted. In 1950 as far as I remember ballast resistor circuits had not been introduced so you need a 12 volt coil, not all that common as from the '60s or even late '50s they all had lower voltage coils with a resistor in series which was shorted out during starting.

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Sat 10 May 2014 18:47
Morris Oxford - Morris Oxford - skidpan

you need a 12 volt coil, not all that common

Not a Morris parts supplier but I have bought lots of parts form Burton Power before and never had an issue.

On this link there are coils for every type of system, no shortage of non-ballasted coils.

www.burtonpower.com/parts-by-category/ignition-ele...l

Personally I would buy the Bosch Blue one.

www.burtonpower.com/parts-by-category/ignition-ele...l

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Sat 10 May 2014 22:09
Morris Oxford - Morris Oxford - focussed

I had one of these! Big old black barge - bought it for £15!

The ignition system is totally conventional - buy a 12 volt coil for a standard Morris Minor and you should be all right with that, but as stated get the polarity the right way round.

www.dsnclassics.co.uk/minor-parts-shop/minor-engin.../

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Mon 12 May 2014 11:50
Morris Oxford - Morris Oxford - Railroad.
The condenser is fitted in parallel to the contact breaker points, and its purpose is to minimise the current passing across them. A faulty condenser is not likely to be the problem. It can only really fail in one of two ways.
1. Open circuit. In this case the current draw across the points would not be supressed, and the points would arc and burn very quickly.
2. Short circuit. The ignition coil would not switch off, and so there would be no HT spark at all and consequently the engine would not start.

The resistance of the primary windings inside the coil is the only resistance in this very simple circuit. The coil connections should be marked '+' and '-', or '15 and '1'. Older coils were marked 'SW' and 'CB'. Connecting a coil the wrong way round could mean the HT spark is weak and could give poor starting and/or a misfire at higher engine speeds.
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Mon 12 May 2014 13:29
Morris Oxford - Morris Oxford - bathtub tom

>>The condenser is fitted in parallel to the contact breaker points, and its purpose is to minimise the current passing across them.

Although a dodgy condenser will result in pitted points, I understand the condenser is to control the CR time, ie the decay of the current that defines the HT voltage.

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Mon 12 May 2014 17:05
Morris Oxford - Morris Oxford - Quicksilver

A 1950 Oxford!! Was it even a 12V system on this car? It is so old it could have been 6V?

Assuming it was a 12V system it will have a standard not resitor ballasted coil. The original one would have had the screw on connections which came long before the push on type.

A 12V standard coil should have a resistance of around 3 ohms. This means that the steady state current will be around 4A. Steady state power will be around 48W so even if it is only active for 25% of the time the unit will get warm/hot.

I used to have several of these lying around from various mini's and minors. I binned them many years ago as there was no use for them.

A good electronic ignition module, (with the correct coil!) will make the car start better and will elimate the points burning.

Good luck!

Q.

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