Insulation of the contacts of the distributor cap burned

[Bertson]

I think this might well be a mechanical assembly issue

Short answer:

remove Pertronics; run with points for a while and see what happens.

consider buying a quality rotor and cap from the Distributor Doctor, not SNGB etc

Long answer:

The distributor shaft top section is a solid unit, and the six sided cam section can't be moved relative to the notch at the top that locates the rotor arm. The top section positively locates on the lower shaft and is held with a screw. It does rotate with centrifugal advance but this doesn't affect the relationship between cam and rotor arm. So under normal circumstances these cannot become mistimed.

It is possible for the distributor drive shaft to be incorrectly timed relative to the crankshaft. We see this pretty commonly on cars we work on.

This either occurs because allowance isn't made for the rotation caused by pushing the drive gear home on the crank, or simply not aligning the shaft properly, up to and including getting it 180 degrees out. However none of this will affect timing per se because you can compensate for it by altering lead position and rotating the distributor.

Furthermore as above the relative positions of the rotor arm and cap are fixed as both are located by notches on the shaft and distributor body respectively. With points fitted I don't think it's actually possible for the spark to be mistimed mechanically.

However the OP has a Pertronics unit fitted. If I understand them correctly, they work by the Hall effect. The trigger is a wheel which is pressed down over the cam section with a magnet located to trigger the unit. Now if this wheel is mispositioned, or the unit itself is in the wrong place on the baseplate then you can well imagine that the spark might be mistimed between the rotor and the cap. If the Pertronics units provide a stronger spark as well (not sure about that) this would potentially worsen any problem.

Hello Abowie,

you have described the Pertronix very well. There are six magnets in the trigger wheel that match the cylinder number.

I think also that the Pertronix has a problem and to install a breaker contact with a condenser will show if the Pertronix is the problem or not. Could be a missposition.

I will try to mill long holes in the base plate of the Pertronix hall sensor to change the position of the trigger wheel to the hall sensor.

I have installed a lambda probe in the first exhaust duct which show me the correct mixture, which is normally optimum. My spark plugs are often very sooty, and power is not that what I expected, especially at high revs.

But first back to breaker contact, is quicker..thank you for the tip I will check...

Best Regards,

Robert

[Bertson]

I think this might well be a mechanical assembly issue

However the OP has a Pertronics unit fitted. If I understand them correctly, they work by the Hall effect. The trigger is a wheel which is pressed down over the cam section with a magnet located to trigger the unit. Now if this wheel is mispositioned, or the unit itself is in the wrong place on the baseplate then you can well imagine that the spark might be mistimed between the rotor and the cap. If the Pertronics units provide a stronger spark as well (not sure about that) this would potentially worsen any problem.

Misplacement of the trigger wheel on the shaft seems the most likely cause and to check I suggest you do a static type of timing check where you rotate the engine by hand with the ignition on to determine the firing point (use a neon indicator in the lead from the coil or monitor the current flowing into the coil). At the point the distributor fires, stop rotating the engine and remove the cap and see where the rotor arm lines up to relative to the contacts in the distributor cap and you'll likely find your problem.

Reverting to points doesn't really help as you'll be sidestepping your problem and the weaker spark is less likely to cause any contact burn.

Hello Johnetype,

yes, but the trigger wheel of the Pertronix could be in the wrong position.
Static test with a lamp as for the contact breakers will not work, because the principle is different. Therefore I always use the strobe pistol and timing is OK.

Normally the ignition point of the Pertronix should be much more accurate than with a breaker contact and I always prefer the Pertronix.
I will check with breaker contacts to eliminate and if these are adjusted very well, the ignition works very well with them. Must only be checked frequently and they must be greased frequently.
I will call the team from Pertronix to check if I use the correct type of Pertronix, because was ot installed by the previous owner.
Thank you for the tip...

Best Regards,

Robert

[Bertson]

Reverting to points doesn't really help as you'll be sidestepping your problem and the weaker spark is less likely to cause any contact burn.

I disagree. It removes the whole Pertronics unit which is the most likely cause of the problem. You can always refit it later and see what happens.

Hello Abowie,

yes, your idea seems logically to me and I will try with contact breakers to to exclude the cause with the Pertronix.
I will mention here in the forum, that the Pertronix is a very good solution, but the problem is, Pertronix was installed by the previous owner...

Could be that the Pertronix was delivered for an etype, but the distributor is for an XJ, build after 1974, could be a small different in the two Pertronix versions, but this could cause perhaps the problem....

I will call the team of Pertronix to discuss my problem.

They should know how to test their own ignition system.

Thank you for the tip...

Best Regards,

Robert

[MarekH]

As you appear to consistently be putting too much energy into the spark and the only non standard part of your setup is a Pertronix 1, I would check the sensor gap inside the distributor to verify that the Pertronix does not have too high a dwell set.

A coil with too low a resistance will also pull too high a current, so I would make sure it is not below 3ohms, which is the Pertronix spec in this case.

Was the XJ 1974 a ballasted ignition?

kind regards
Marek

[MarekH]

My thoughts are that if this Pertronix board expects to run a coil from a ballasted voltage, then it is permanently in cranking mode if always at 12v.

kind regards
Marek

[MSM]

As you appear to consistently be putting too much energy into the spark and the only non standard part of your setup is a Pertronix 1, I would check the sensor gap inside the distributor to verify that the Pertronix does not have too high a dwell set.

kind regards
Marek

My understanding of the Pertronix set up is that there are no adjustments, other than setting timing, and the dwell angle is permanently set.

The other possibility is that, given the rotor arm appears to be out of sync with the connections in the cap, is the Pertronix magnet wheel correctly positioned on the shaft?

[MarekH]

The other possibility is that, given the rotor arm appears to be out of sync with the connections in the cap, is the Pertronix magnet wheel correctly positioned on the shaft?

If not all of the terminals are similarly affected, is the cap properly centred and attached to the distributor?
The installation of the Pertronix board ought not interfere with the relative geometry of the other parts.
Cut up one of your spare caps to check
kind regards
Marek

[MSM]

It would also be interesting to see the state of the rotor arm tip.

[Bertson]

My thoughts are that if this Pertronix board expects to run a coil from a ballasted voltage, then it is permanently in cranking mode if always at 12v.

kind regards
Marek

Hello Marek,

Sorry but do not understand the part: "if this Pertronix board expects to run a coil from a ballasted voltage, then it is permanently in cranking mode if always at 12v."
Currently I use a Lucas sports coil, resistance is higher than 3 ohm.

You are right the gap between trigger wheel and pickup must be correct, yes I have adjusted correctly.
All contacts are burned in the same way.

Best regards
Robert

[MarekH]

Dear Robert,
I am trying to reconcile how it could be that you consistently keep putting too much energy into the distributor cap, time after time and the only non standard part of your setup is a Pertronix electronic ignition.

The way most electronic ignition sytems work goes like this:-

It is very hard to start a car with a cold engine but easy to keep a car running or restart a warm engine. To accommodate both difficult starting and easy running, electronic ignitions reconcile these two scenarios by running the coil via a ballast resistor.

During cranking, full 12v goes to charge the coil and provide a big powerful spark, but once the engine starts, the starter motor diverts the 12v to charge the coil through a ballast resistor, so the coil charges from only about 9v instead of 12v and produces a weaker spark. The coil ohmage specification is set so this lower charging voltage is the norm, but briefly running it to charge more only at start is tolerated.

The Pertronix appears to be a setup which always runs from 12v, but it isn't obvious to me whether the circuit is internally ballasted, maybe set via a timer, such that for the first five seconds of startup, it puts out a big spark, but then cuts back to a weaker spark for general running. Some ignitions demand to be connected by a specially provided wire which incorporates a resistance, so their wiring diagram looks normal, but a ballasted voltage is being provided to the unit during normal running because their wire means a lower than 12v supply is running the ignition, even though you don't realise it.

I am simply trying to work out a scenario whereby you are in the position of always putting too much energy into the distributor cap. If the Pertronix you have expects to run from lower than 12v during normal running, then you may be accidentally "running it hot" and although the coil can take it, the distributor caps can't.

To get to the bottom of this, you really need to have the exact specification of the ignition unit and make sure it has the correct components connected. It obviously isn't supposed to put oput so much energy as to keep burning distributor caps, so if it isn't misalligned, is together with the right spec omponents, then is somehow not running the way you expect it to be internally.

If you cannot reconcile why or how there is too much spark energy, then simply running the ignition through a ballast resistor may solve your problem:- it'd only see full power during cranking and a slightly reduced energy spark during normal running, if the electronics in the unit allow for such solution.

kind regards
Marek