• Hi Guest!
    If you appreciate British Car Forum and our 25 years of supporting British car enthusiasts with technical and anicdotal information, collected from our thousands of great members, please support us with a low-cost subscription. You can become a supporting member for less than the dues of most car clubs.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

the coil?

Share this page

IF your car is negative ground you connect the coil (-) terminal to the distributor. On older Lucas coils (used on positive ground) the markings were SW and CB for Switch and Contact Breaker. Most ground conversion articles I've seen focus on that coil when they talk about moving coil connections.

EDIT: I have deleted my next three posts because they were an exchange between Keoke and myself that did not add to this thread.
 
Hi TH, If your car is "NEGATIVE GND" then the NEG terminal{-} of the coil goes to the Lucar connector on the dizzy.Otherwise they connect in reverse.---Keoke
 
HI DK, That is not the problem. If the coil terminals are in reverse the polarity of the spark is wrong at the plug you want a NEG spark there. If reversed the secondary high voltage will need to increase about 20% to jump the gap. This voltage increase can over stress the The wiring rotor cap etc.---Keoke
 
DK ,it is well documented in most repair motor books and can very easily be seen on the analyser screen.---Keoke /ubbthreads/images/graemlins/yesnod.gif
 
OH DK, try this search:"Why are there many different types of sparkplugs"---Keoke
 
[ QUOTE ]
Keoke, I've heard that sort of argument before. Until I see technical proof (I mean an o-scope trace showing what the peak voltage is) I don't believe it.

The polarity of the spark is "wrong"? The coil works when the low tension field collapses. This collapsing magnetic field produces voltage in the secondary winding. The magnitude of the voltage in the secondary winding is proportional to the voltage in the primaries by the winding ratio of each. Exactly how does a collapsing magnetic field increase by 20% the energy in the secondaries without changing the number of secondary windings?

[/ QUOTE ]
Hi Doug,
I'm sure that you know the common theory:
Electrons flow from negative to positive electrodes.
Electrons are emitted more freely by a hotter electrode, ie. the old vacuum tubes with a cathode heater.
The spark plug center electrode is hotter than the ground electrode.
So:
A hotter center electrode that is negative with respect to the ground electrode should require a lower voltage to ionize the spark gap & vs.

How much lower the required voltage, is subject to how much hotter the center electrode is than the ground electrode & possibly other variables. Possibly 20% under the right conditions. I have never seen a scope trace or other measurements that would quantize this "lowered voltage requirement". I think any benefit would only happen if the ignition was marginal to start with.

In any event, the coil primary & the secondary will only build the voltage level that is necessary to ionize the spark gap. Once this ionizing level is reached, the voltage required to maintain the spark is considerably lower.

In the real world, I have found no practical difference in engine performance with either spark polarity. Maybe Just not in the right place at the right time?
Later,
D
 
Okay, excuse the ignorance but if I have neg ground (the block)and the center of the plug is neg, how does the spark flow from center post to the outer electrod if it is seated in the block ?????? I am so confused. But I will connect as instructed. It wo;rked before. I just don't see the logic.
 
TH,Read the search item I posted it is pretty straight forward. The center electrode is not grounded and it is full of free electrons that can move and they are attracted by a amore positive potential the block. It isn't logic its Physics. I just don't like giving lessons. Dave pretty much covered the underlying factors---Keoke
 
[ QUOTE ]
Okay, excuse the ignorance but if I have neg ground (the block)and the center of the plug is neg, how does the spark flow from center post to the outer electrod if it is seated in the block ?

[/ QUOTE ]

Hi TH,
Since the coil windings are separated (electrically insulated) from the coil housing (metal), the coil can be connected with either side of the primary, (small terminals) to ground through the points. Which way the two terminals are connected determines the polarity of the spark independently of which way the battery is connected. In the case you mention, ignition secondary (high voltage) ground is actually positive with respect to the coil HV output although the rest of the circuit grounds may be negative with respect to the battery connections. See this reference for operation of the "Kettering" ignition system:
https://users.mrbean.net.au/~rover/ketterin.htm
D
 
Back
Top