407 Coil Failure

[Barrie]

A pal has a 407 on which he's spent much money but there is a problem defeating him and his advisors.
The coil originally failed by leaking all its oil after the ignition was left on for 30 mins. Since then there have been two further brakdowns to the point where the coils cut out and each caused a failure to proceed. This was remedied by allowing them to cool down.
It all suggests that the coils are overheating.
Any ideas why this should be?

[Stefan]

May need a resistor inline with the 12v supply, this can be bypassed in the 406 for starting.

[John Simmons]

Stefan is correct. I had this exact same problem in a 404 (Arnolt) when I first purchased it (used). Somebody had bypassed the resistor. This will also burn up the points. My 40 year old memory says you want about 9 volts to the primary side of the coil.

I don't know the configuration in a 407, but here's a picture showing a typical resistor (lower left) and coil.

[Nick Challacombe]

Odd one that, I would have a word with Martin Barnes at ACCS. I have had my 407 for 16 years and never have had a problem with coil, dynamo or starter. I have changed the regulator once, essentially the electrics on the 407 are very simple. I have not changed to an alternator as the electrics were not designed to take it. I have kept to positive earth and not added any extra load.
If any body has had the problem I an sure Martin will have heard of it as he specialises in American V8's.
Nick

[Julian Caples]

Barrie

The two issues with the coil may not be directly related (except in that they both involve the coil)

for all of the below, I assume that you are still running the original points system (i.e. it hasn't been replaced by an electronic ignition system of some sort)

Re the initial burning out of the coil: this can (and does) happen if the ignition is left switched on without the engine running for a significant period of time if the points are closed. under such conditions the points complete the circuit to earth and the coil draws current continuously - it will overheat after a time if this happens, just how long depends on the quality of the coil. depending on how you have the points set up, you have about 160 degrees chance out of 360 (so a bit less than 50:50) depending on exactly where in the cycle the engine stopped when last turned off.

I suspect this is what happened in this case
As a general recommendation, if you are going to switch the ignition on without the engine running for any period of time (e.g. electrical work), then disconnect the coil (sw terminal - white and yellow wire on the 407 if it still has the original colour coding)

Re the current overheating of coils: this is strongly suggestive of using coils that are designed for use with a ballast resistor without the resistor.
whilst it is a little difficult to diagnose by forum (i.e. without seeing the car), the first place i'd look is the ballast resistor.

the 407's original ignition system does have a ballast resistor (and it is bridged out during starting by a ballast relay that is switched by the starter solenoid).
I can only guess what has happened in the past, a typical scenario goes something like this:
1) coil needs replacement and a 'non resistor' coil is procured and installed by mistake - the car will start well, but run very poorly (because the resistor that is in circuit during normal running effectively halves the voltage to the coil)

2) in an attempt to rectify this, someone removes (or shorts out) the resistor and that 'cures' the problem and the car runs fine now (well it's harder to start, particularly when very cold or when the battery is getting a little tired, but it runs 'just like it used to')

3) now the mistaken coil burns out and is replaced by a correctly specified coil (a 'resistor type'), but now running without the resistor - this means that when running the coil will 'see' twice the voltage it is designed for - it will inevitably burn out

So, how to diagnose and deal with this
is there a resistor? (see the picture on john's post - the resistor is the rectangular white object with a wire on each end) in the 407 it should have a white wire attached to one end and two white and yellow wires attached to the other.
if it's there, is it connected? or has it been bridged out (e.g. a wire placed from one terminal to another)

if the resistor is all in order, the next place to look is the ballast relay - if that has an internal short or is stuck closed, then it is effectively shorting out the resistor all the time

cure - install resistor correctly and use with correctly specified coil, replace ballast relay (and verify correct operation during starting)

the (NOT RECOMMENDED) alternative to problem solving and rectifying the problem is to replace the coil with a 'non resistor' coil - this resets the car to the same state as the original 'bodge' - the car will run fine, but may be more difficult to start than it needs to be - sadly this is a common solution (one that the makers of aerostart are most grateful for :-))

hope that helps

Julian

[John Simmons]

Julian covers it thoroughly.

Just to clarify a bit regarding the ballast relay. On the (1966 vintage) Chevrolet 283 V8 in my Arnolt, the ballast resistor bypass wire originates from a terminal on the starter solenoid, so there is not a separate relay. The relay (or contact) is internal to the starter solenoid.

I don't know the configuration with the Chrysler engine.

John Simmons

[Julian Caples]

The 407 does have a relay

you must have either a relay or a diode in the feed from the starter solenoid or you will have power fed (at about 8-9v) from the coil feed back to the starter after the engine has been started - this is unlikely to be a good thing

the other method for bypassing the ballast during starting is a separate circuit independently switched from the ignition key (i.e. when turning the key to the 'start' position, it activates two independent circuits - one for the starter solenoid and another that bypasses the ballast)

John's chevy installation must have a diode or relay in the solenoid (i.e. specific terminal for a ballast bypass that does not allow feed back to the solenoid)

regards

Julian

[Nick Challacombe]

Barrie,

My 407 wiring diagram clearly shows a ballast relay between the coil and the starter. A white wire when built goes from C1 on the ballast relay, through the fuse and ignition switch to ignition warning light and then the control box. A white and red wire leave the ballast relay from W2 and goes straight to the starter. From the ignition coil a white and yellow wire join with a white wire at a ballast resistance where it leaves as a white/yellow wire onto C2 of the ballast relay
I have a spare Instruction Manual and a spare, Spares Handbook should your pal wish to purchase them.
I do not want to confuse but the wiring diagram I believe is also available on the BOC web site.
A hand book is always a good thing to have. I even have a Brand New Instruction Manual and Spares Handbook, never been in a car but in my archive.