Advice - when I last changed the spark plugs on my Corolla, the Toyota garage told me that it had to be done by a 'proper' dealer, as along with changing the plugs they hooked the engine management into a computer to set the engine up afterwards.
Is this true, and do independent (cheaper) mechanics have access to this sort of gear ? If not, does that mean independent mechanics aren't setting your car up properly after a spark plug change ?
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Provided there are no pre-existing faults the engine should not require 'setting up' after a simple plug change. Just set the plug gap correctly and don't over-tighten the plugs in the head.
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Just make sure you use the correct plugs though, I once changed the plugs on a Rover 216 (old Honda accord shape) and put normal plugs in, instead of resistor type, and the ECU did not like it at all. Changed them to the correct resistor type and all was well.
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Thanks both for the reply - now I can go off and use my local independent and save a lot of cash !
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Check that you use the correct tightening technique. I think some plugs you tighten to a specific torque, which you usually guestimate, others to a particular amount and then half a turn, or something like that. Depends on the kind of washer, I think.
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Reason for different tightening methods is not the washer but the plug type.
Some plugs have a tapered thread whereas others have parallel threads, obviously overtightening a tapered thread could have dire consequences!
Good idea to use an old plug with hacksaw blade cuts in the threads to clear out any carp, it's a little extra time but you'll know you've engaged the threads properly and not cross-threaded by the ease in which the plug does up.
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Thanks Malcolm. But isn't there something important about washers? Some compress on first tightening, and either shouldn't be reused or need a different torque the second time?
I know the days of cleaning and reusing plugs have long gone, but it still makes sense to remove and check them in between replacements, if only to stop them seizing up - a frequent forum topic.
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Sorry, Malcolm_L, but ALL spark plugs have parallel threads.
The 'taper' is the sealing part of the plug (at the opposite end of the threads to the firing electrode).
Many vehicles use spark plugs without this taper, and they rely on a compressable washer to seal the gasses.
When tightening spark plugs, wind in by hand until touching, then tighten the final stage using a ratchet.
Washer type - 1/8th of a turn.
Taper seat - 1/th of a turn.
Make sure that you spark plug matches the type of seat in the cylinder head. The washer will fit a flat surface, the taper will fit into a chamfered one...
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Try this URL for more technical info:
www.spark-plugs.co.uk/
I use a small 3/8" drive torque wrench when putting plugs into alloy heads - avoids the guesswork. I also clean the threads using a plug 'thread chaser' (few ££ from a tool factor) and put a spot of copper grease on the new plug threads. Never had a problem.
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Changing the plugs on my 1.0 Yaris was a simole job, and well worth the time. Even though I've only done 10K in 3 years in getting smoother running and another 1 mpg better economy.
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