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Old 13-04-18, 06:51 AM   #11
Craig380
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Default Re: Spark plug observations

Iridium isn't as good an electrical conductor as copper, it's true. But because it's a much harder metal, the electrode tips can be made much narrower and more pointy (pointy, geddit ) than with a conventional copper-cored iron-tipped plug.

This lowers the actual voltage required for the spark to jump the plug gap, which means for a given HT voltage from the coils you get a more reliable spark in marginal conditions (such as in a old 70s 2-stroke with an over-rich, oily fuel mixture, or in a high-output turbo engine, in which high boost pressures can literally blow the spark out).

As pointed out above, rare-earth plugs will also wear less. But as I said in my original post, conventional plugs don't wear much at all in SVs either. You pays your money ... although the price gap for a pair of Iridiums isn't that much more than a pair of ordinary plugs these days.
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Old 13-04-18, 07:20 AM   #12
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Default Re: Spark plug observations

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Originally Posted by R1ffR4ff View Post
Yes but in your previous post you made a point of saying that the lower resistance of Iridium would be beneficial which is fact incorrect as Iridium has a higher resistance.

Also resistors are fitted to Spark plugs to suppress Back EMF from interfering with the ignition circuit.
As costs have come down Iridium plugs have been fitted by most car makers for a few years now, both our Honda cars came with them as standard.

I never said Iridium had lower resistance than copper alloy, what I said was that due to the small diameter (made possible by heat resistance and hardness of Iridium) an Iridium tip needs lower voltage to form a good spark. Due to the fact that spark voltage is over 20KV and very low current a piddling little extra fraction of an Ohm in the circuit caused by bulk resistance of Iridium slug is neither here nor there, to put it in perspective the integral suppressor resistor in plug body is 5000 ohms.

http://www.ngksparkplugs.com/about-n...tor-spark-plug
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Last edited by SV650rules; 13-04-18 at 07:24 AM.
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Old 13-04-18, 07:54 AM   #13
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Default Re: Spark plug observations

It only needs 7kV to jump the gap on a Spark plug.

The 2017 SV650s come with NGK MR8E-9 Platinum plugs.

https://ultimatemotorcycling.com/201...12-fast-facts/



Also I like to take my plugs out and check them from time-to-time as they give a good indication of how the engine/mixture is running but it's easier for me to get to my front plug on a,"Naked" and especially as I've removed the horn bracket and only have to remove the three Rad bolts and push the Rad forward.

At the end of the day it's down to what the user finds runs best for their machine.My 1999 curvy runs better on standard copper Plugs.

HTH
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Old 13-04-18, 09:39 AM   #14
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Default Re: Spark plug observations

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Originally Posted by R1ffR4ff View Post
It only needs 7kV to jump the gap on a Spark plug.


The gap should be 0.7mm which at 30kV/cm for discharge is actually 2.1kV for spark.
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Old 13-04-18, 09:40 AM   #15
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Default Re: Spark plug observations

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The gap should be 0.7mm which at 30kV/cm for discharge is actually 2.1kV for spark.
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Old 13-04-18, 10:20 AM   #16
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Default Re: Spark plug observations

Hi, Ive always worried with running plugs for very high milages about the risk that the ceramic around the electrode might break up. It is subjected to high temperatures plus more importantly thermal cycling and of course if it fails could cause a lot of damage....
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Old 13-04-18, 10:24 AM   #17
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Default Re: Spark plug observations

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Hi, Ive always worried with running plugs for very high milages about the risk that the ceramic around the electrode might break up. It is subjected to high temperatures plus more importantly thermal cycling and of course if it fails could cause a lot of damage....
My concern with plugs that may not be touched for a long while and having been through it,is welding to the cylinder head.

Sometimes it's an advantage to have to make regular service checks and break the seal on Spark plugs I've found.

This is the same reason I'm happy with Standard coolant and renew it at least every two years as I then flush my cooling systems before putting fresh coolant in.

My 10 penn'th.
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Old 13-04-18, 10:53 AM   #18
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Default Re: Spark plug observations

Long life Iridium and platinum plugs have a special tri-valent nickel plating on threads which is designed to resist sticking to aluminium of the head, it is much superior to passivated zinc or cadmium plating of normal life plugs. I changed the OEM fitted Iridium plugs in my Honda Civic last year at 70,000 miles and they unscrewed very easily (in fact much easier than normal plugs I have changed at as little as 7,000 miles). Also changed plugs in wifes Jazz at 65,000 and they came out easily. Modern ceramics are leaps ahead of older ceramics as well in terms of heat resistance and breaking up.

The difference between a spark jumping a gap in free air at normal pressure and doing the same at higher pressure and heat of the combustion chamber (where mixture can swirl and try to 'blow out' the spark ) also has to be taken into account. But the end result is that finer tip of Iridium (or even better Platinum) plugs can focus and stabilise the spark. Some plugs with multiple ground electrodes (Bosch seem to favour these but warn against using them in Japanese engines) work on the fact that electricity will always take shortest path and when one gap has opened up due to erosion of the side of one ground electrode and ground electrode opposite the spark will go to next ground electrode and a fresh place on side of centre electrode and ignore the largest gap, thus offering 4 erosion points instead of 1.

The spark actually happens when power is removed from ignition coil and the magnetic field collapses, because the discharge path of primary coil (higher current low voltage coil, few turns of heavier gauge wire) is electrically blocked (by open points or a transistor that is turned off = non conducting state) the voltage in secondary coil (high voltage with many turns of smaller gauge wire) will rise until it is high enough to discharge its energy somewhere (across the spark plug gap hopefully) if the gap is larger than it should be the voltage will rise until it can jump the gap, if the gap is too big this voltage can rise high enough to break over the coil electrical insulation and once that happens the coil often fails. So the time power is applied to the coil (called 'dwell time' actually charges the magnetic field, and when power is removed from primary coil the energy stored as a magnetic field will create a spark on the secondary coil side).

interesting article here http://bustekhub.com/index.php/2016/...ark-plugs-101/
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Last edited by SV650rules; 13-04-18 at 11:50 AM.
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Old 07-01-19, 03:51 PM   #19
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Default Re: Spark plug observations

A quick update to this: another 7,000 fastish open-road miles later, I thought I'd check the Iridium plugs again. They were in perfect nick, and the gaps had not changed. So basically, if you've got a K3 to K6 pointy, unless you start getting a misfire, Iridium plugs hardly ever need checking
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Old 07-01-19, 04:08 PM   #20
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Default Re: Spark plug observations

you only check plugs if your having problems.
you only change plugs as per manufacturer recommendation or your having problems.

dont keep checking modern plugs especially thin walled ones like the SV has. you will crush the sealing washer too much and put more stress on the threads.
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