Originally spark plugs had the earth above the centre electrode and as the electrode eroded the gap got bigger.
Modern plugs have side earths - even with a single earth that gives two spark paths, one from each corner - using quad plugs will give 8 spark paths so last a very long time.
I'm genuinely puzzled by your comment above. As far as I knew the ignition lead attaches to the centre electrode which is sealed in the ceramic insulator, the side electrode is welded to the threaded portion screwed into the head and therefore the side electrode forms the earth. Back in the 1960's I remember Lodge introducing plugs with 3 side electrodes, I was never aware of another earth path above the centre electrode?
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Originally spark plugs had the earth above the centre electrode and as the electrode eroded the gap got bigger.
Modern plugs have side earths - even with a single earth that gives two spark paths, one from each corner - using quad plugs will give 8 spark paths so last a very long time.
I'm genuinely puzzled by your comment above. As far as I knew the ignition lead attaches to the centre electrode which is sealed in the ceramic insulator, the side electrode is welded to the threaded portion screwed into the head and therefore the side electrode forms the earth. Back in the 1960's I remember Lodge introducing plugs with 3 side electrodes, I was never aware of another earth path above the centre electrode?
My bad - my assumption of "above" is with the plug out and being examined - for most cars that's "below" when installed.
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The "Golden Lodge" plugs came on the market in the (early?) 60s. They had golden looking metal and 3 wider side electrodes than the ordinary Lodge 3 sided electrode spark plugs of the time. They were supposed to be last longer and give a better spark, which I think they did. But they also cost as bit more. A spark plug invariably cost 5/- (25p) then and was that price for a long time. A classic case of inelastic supply and demand economics as not many manufacturers produced them but all cars etc required them and to be replaced regularly.
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Modern plug life has been improved by plating the side electrodes with Copper(C) and then both electrodes(CC)-then moved on to Platinum(P & PP)-now it's Iridium!
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Its quite amazing how much spark plugs have improved over the years I took some out of a 2003 Mercedes with 155kkm use and they were like new I suppose they are made to last about 160kkm around 40 years ago you were forever setting them and exchanging them .
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Modern electronic ignition may be easier on the plugs than the old coil and contact breaker/condenser system? Unleaded petrol doesn't build up deposit on the electrodes either as the old 4star used to, no doubt present fuel additives also help keep plugs clean.
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Modern hard materials like iridium are 95% responsible. Remember how plug tips eroded within 4-5k miles 40 years ago? Sofy materials - you could bend the tips. Try bending iridium - it will break,
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Iridium plugs are excellent for classic cars and bikes too -- especially old 2-strokes like mine. The narrow centre electrode means a good spark even with marginal, 40+ year-old electrical systems and the oily soup that passes for a 'mixture'.
I've found they never oil up, nor need gapping on my Suzuki GT: just fit and forget. They're also pretty cheap these days from online shops.
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Will need to fit a set to my CB500 soon, do you buy these Iridium ones pre-set to the correct gap, or do you still have to set them yourself with feeler gauges?
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Will need to fit a set to my CB500 soon, do you buy these Iridium ones pre-set to the correct gap, or do you still have to set them yourself with feeler gauges?
They do come gapped to 40thou / 1mm but for my bike I set the gap to 25thou (I'm still running points ignition, which needs all the help it can get!).
If your CB is a modern one with CDI, I'd just fit them as they are out of the box.
It's worth noting that the plugs have a 5K ohm resistor as standard, so you might want to order some NGK non-resistor type plug caps (I got mine from http://www.sparkplugs.co.uk/, the part number is LZFH, a pound each)
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Will need to fit a set to my CB500 soon, do you buy these Iridium ones pre-set to the correct gap, or do you still have to set them yourself with feeler gauges?
They do come gapped to 40thou / 1mm but for my bike I set the gap to 25thou (I'm still running points ignition, which needs all the help it can get!).
If your CB is a modern one with CDI, I'd just fit them as they are out of the box.
It's worth noting that the plugs have a 5K ohm resistor as standard, so you might want to order some NGK non-resistor type plug caps (I got mine from http://www.sparkplugs.co.uk/, the part number is LZFH, a pound each)
Points ignition - that takes me back - electronic ignition designed for retrofit from those days is nothing more than an amplifier, which means that the current across the points is very low reducing pitting yet the output voltage is high giving high voltage at the plugs when multiplied up by the coil.
However, the gap determines the spark voltage - it jumps as soon as the voltage is high enough to cross the gap - increasing the gap will increase the spark voltage.
Just a thought for you.
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Points ignition - that takes me back - electronic ignition designed for retrofit from those days is nothing more than an amplifier, which means that the current across the points is very low reducing pitting yet the output voltage is high giving high voltage at the plugs when multiplied up by the coil.
However, the gap determines the spark voltage - it jumps as soon as the voltage is high enough to cross the gap - increasing the gap will increase the spark voltage.
Just a thought for you.
That's true, but with the original battery / coil set up a big plug gap can be too much. There's a pretty big aftermarket for optical- or magnetic-trigger electronic ignitions now which do away with the points, condensers etc entirely, but points don't need that much adjusting if you keep the cam lubricated to reduce wear on the fibre 'heels'
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Iridium plugs are excellent for classic cars and bikes
Seem to be the 'in' thing for LPG users in the know too.
Certainly a new set of those perked up the running of our LPG Outlander.
Whats the current thinking about periodically removing plugs...or indeed glow plugs on a Diesel, and cleaning the threads up before re-inserting.
I ask because some engines are prone to seizing the glow plugs solid after some years in situ, only hear of rare problems with broken or stuck spark plugs but if an vehicles prone to this it would make sense.
Also, what to DIYers and mechanics here do when fitting spark or glow plugs, dry and clean threads, coppaslipped, oiled?
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I put a dab of copper ease on the new spark plugs before I put them in.
I had to buy a small torque wrench for the old BMW. I had a ticking noise coming from the engine that scared the hell out of me. Failed hydraulic tappet? Small ends, big ends going? No, I took it to my garage and they diagnosed a loose spark plug with a stethoscope.
I hadn't tightened them up properly and after a while one of the spark plugs worked loose and a small amount of gas was leaking out of the spark plug aperture. But it sounds very metallic - something that only someone with experience would recognise.
It amazed me how much more I had to torque them up to do the job properly, being scared of over tightening with the alloy head. It takes a few more turns to compress the washers.
Funnily enough, Car Mechanics magazine is doing an article on seized injectors in the Feb issue.
Edited by corax on 01/01/2014 at 12:05
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Car Mechanics magazine is doing an article on seized injectors in the Feb issue.
Thanks Corax, i'll try to remember to pick one up.
Should subscribe really, about the only mag of any description that i look at these days.
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When I had a clapped out Wolseley 4/44 - it wasn't so old either - one of the cylinders must have had fragmented rings and so the spark plug oiled up and ceased to spark. A local garage owner sold me a plug with a longer central electrode, in reality a shorter insulator, that ran hot and solved to fouling problem.
My brother once showed his daughter's boyfriend how to gap plugs and found that he couldn't get any of them out. The boy had bought the car only a short while previously under the understanding that the dealer had given it a full service. Not wanting to break anything my brother phoned the dealer. Unbeknown to my brother his neighbour had been watching, and knew the dealer personally. The neighbour knew that my brother was a police sergeant and had already warned the dealer that the police were becoming involved. The car then got a very good service.
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Don't forget that plugs haven't become coated with lead oxides for 20 years or more. That must make some difference?
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Its quite amazing how much spark plugs have improved over the years I took some out of a 2003 Mercedes with 155kkm use and they were like new I suppose they are made to last about 160kkm.......
I have just bought plugs for my 130,000m Audi A6 2.8. I last changed them at 80,000 and kept the old plugs which the service record showed had been in since 40,000, the recommended mileage for changing. They look almost identical to the new ones, and have an identical 45-50thou gap between the virtually unworn central electrode and the two side earths.
Can't really see the point of changing them yet. It is clearly a far too conservative recommendation to change at 40,000. Surely a correctly gapped spark plug either works or it doesn't.
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The official line is the materials although looking ok will break down and not give the correct performance I can only go by my own experiences which tells me that is stretching the truth.
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The official line is the materials although looking ok will break down and not give the correct performance I can only go by my own experiences which tells me that is stretching the truth.
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The spark does gradually erode the two surfaces, widening the gap - modern material and multiple side earths give much longer life than they used to but they won't go on for ever.
They could no doubt last longer than specified - but only with a proper inspection in between - if they're out for inspection you might as well put new ones in!
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They could no doubt last longer than specified - but only with a proper inspection in between - if they're out for inspection you might as well put new ones in!
Yep, will do, and if the 50K ones look as good as the 40K ones [which I suspect they will] I shall never ever buy any more! If the car and I are still going after after another 50K, I shall put the 40K ones back in.
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