Faulty aftermarket Champion plug caps

[abowie]

We have recently had three sets of these plug caps fail on installation.



The first two cases occurred while setting up newly rebuilt engines. In both instances the engines would idle to be tuned but would run very poorly under any load on road testing. In both cases when measured with an ohmmeter all caps had essentially infinite resistance.
Today I put a third new set on my 4.2, which runs perfectly. Before installation I measured the resistances of all caps out of the bag. They were all near as perfect at 10 kohm. I then took the car for a drive. Within 20 km I began to notice some missing and hesitation under throttle. Within a further 5 km the car was pretty much undrivable except under minimum throttle. I then replaced the caps with a set of old, known good ones. Car has now run perfectly for another 30 km.
I have just rechecked the resistances on the third set of caps and they are all now infinite resistance.
I bought the third set from SNGB in September of last year. The other 2 sets came from David Manners. They are identical, with the 10 kohm stickers.
If your car is misfiring and you have these caps fitted take them off and check them with an ohmmeter. They may be faulty.
I will send an email to SNGB to let them know as well.

[jag68]

About 10 years ago I bought a set of caps like yours from a local N.A. supplier. They measured 10k - 15k resistance. A couple of years later when again tested they showed infinite resistance, but surprisingly the car shows no effect from this - that is it continues to run fine. I run steel core wires, non resistor plugs and I make sure the distributor cap doesn't have the resistor graphite center electrode, so is this the reason it still runs?? David Vizzard in one of his excellent books makes the observation that the plug circuit always has infinite resistance ultimately because of the air gap in the spark plug, so minor problems in the wiring are truly minor in comparison. I note that some of the suppliers (can't recall who now) now have these Champion caps with a solid brass center.

Terry Sturgeon

[PeterCrespin]

In my younger days riding anything with an engine around local fields, I recall a stinky old two stroke that fouled plugs regularly. It was probably me using completely the wrong grade and putting treble the amount of sump oil in the petrol instead of low-ash 2-stroke, but what does a 13-14 yr old know?

I read an article in one of the old-school bike publications that had reader's tips and recall advice to cut the plug lead in half and shove both ends into a piece of transparent 1/4" petrol line leaving a gap of about 1/4".

With 20:20 hindsight this was probably ambitious for a tired flywheel magneto, but young legs could kick or push the bike forcefully enough to start it. The idea was that by forcing the spark to jump a 1/4" gap en route to the plug, it would be strong enough to jump a fouled plug into life. It seemed to work and the idea surfaced every decade or so later, as go-faster widgets supposed to give more power, better fuel economy and help you leap tall buildings in a single bound.

[cactusman]

I had exactly the same thing. Mine were marked as 5K (5000 ohms). One failed within a few miles and a second went open circuit after a couple of hundred. I hacked one open. The other four seem oK....for now. I got a load of spares of ebay and carry a couple with me!

SNG Barratt/ebay sellers (Dave Manners etc) here is the reason. Original ones used carbon composition (carbon rod) slugs as the resistance element. Tolerance probably +/- 20 % but fine. Most importantly they are robust and immune to high voltage arcs etc. The new FAKE ones use metal film resistors - at least mine did. Two end caps on a ceramic rod that has been sputter coated with metal film and then a diamond saw used to cut a spiral to obtain the appropriate resistance. Put several thousand volts across it and you get arcs from one spiral turn to the next. Metal film burns away and hey presto. Open circuit. The car will probably run as the spark will jump the now open resistor and the plug gap but your spark at the plug will be weak.
SO...who ever makes the "repro" ones use carbon compossition resistors and NOT the metal film ones I found in mine.

[abowie]

I have had no further information from SNGB although they have agreed to refund me for 2 sets of caps.
I have fitted some NGK LB05EH's which are working well.