Changing the sparkplugs on an MX5
Posted by Maurice | Posted in Servicing | Posted on 04-03-2010
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Today’s the day I begin in earnest – the sun is shining and I’m kitted out. Maurice has almost croaked and just managed to limp pathetically up the driveway this morning – it’s a sad sight on such a beautiful day. Anywho, crap happens as they say – no whizzing around with the top down for me today – bummer 
Since I changed the air filter my little MX5 sounds very sporty but doesn’t perform like it, so I change the spark plugs. I got my natty service kit inclusive of four new NGK spark plugs, so I consult The Book. I do as instructed – pop the hood; check. Find the HT leads; check.
Pull them out by the boot not the cable; not quite check. By the boot I’m assuming The Book means the fat end as the cable goes into the engine block – that’s fine, except I think there is more than a little bit of vacuum as they haven’t been out for a while. Two I manage to wiggle out – but the others? the temptation to pull on the leads is almost unbearable. I’m not very patient, so I decide on my usual tack of lots of profanity to build up sufficient internal rage that gives me enough strength to pull an elephant through a porthole.
It works; I pull out the remaining two leads and apologise to the binmen for my language, as they approach my wheelie bin looking absolutely terrified. The leads are different lengths so it’s obvious to an idiot which hole they go back into – so I see no need to mark them as The Book suggests. I’d bought a 10mm spark plug socket from Ebay and a torque wrench with extender bar as the sparkplugs are deep in the engine block. They take a bit of unscrewing as the threads are quite long but they came out easily – no bad language required.
New spark plugs, I read somewhere, are supposed to come with preset gaps – the NGK ones I bought needed a little adjustment – so it was just as well I’d bought a gap gauge tool to set the gaps to the required 1.1mm.
They needed a little widening, so a gentle prise upwards with the gauge blade was enough to get the desired gap. As the threads on the plugs are only fine and soft, it’s very easy to cross-thread them – The Book suggests a length of hose to put them back in to start off with. So, I hacked a piece off the garden hose. It was just slightly too narrow so I used the extender bar from the torque wrench to start them off. I then clipped the wrench back on to tighten them to the correct torque – 15-22 Nm or 11-16 1lb ft. I popped the HT leads back in the engine block – they go back in far easier than they come out and then had a look at the spark plugs that had just come out.
Hmmm. Very black with lots of carbon – I revisited my earlier post of How Do Spark Plugs Work? to see if it would give an indication of Maurice’s health. Not really; but apparently I drive like my Grandma 
Eagerly, I hopped into my little knackered MX5 and started the engine to see if he sounded any different. The answer? is no – he still sounds like an asthmatic in a hay barn. Oh well – at least he started, so that means I got the spark plugs right. I’m beginning to think that Maurice’s asthma is not going to be solved by a mere service parts – a bit of sleuthing is needed so I’m off for a bit of online investigation.
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