General Spark plug gaps

[FuzzyPanda]

I gave my car a service a few weeks ago which comprised of oil, filters and spark plugs. The plugs were NGK items and the gap was not adjusted as it appeared to be near enough correct (had the Haynes out, but can't remember the setting it said).

Since the service the car has a very slight rattle from the engine, I think this is what could be commonly desribed as pinking, but I'm not entirely sure. I ran half a tank of V-Power last week to see if any deposits were causing problems, but the noise remains.

I suspect the gaps on the spark plugs aren't correct, but I don't have any knowledge of what adjusting the gap does, the best way of doing it, or whether it's causing the rattle. The oil used was 10w40 Semi synthetic, which I have used since purchase with regular changes, so can't see this being at fault.

Any ideas?

 

[Nuova500]

pinking is caused by too much ignition adavance, i.e. too far advanced timing or too big a gap on the points, but you dont have them do you? never heard of plug gaps causing it, but I suppose if the gap is too far out youll get problems.

 

[Steven]

From memory the gap should be 0.7mm. You shouldn't really be guessing the gap. A cheap gap feeler like this one on eBay will let you set the gap accurately.

http://cgi.ebay.co.uk/DRAPER-METRIC-SPARK-PLUG-GAP-FEELER-GAUGES-10-BLADES_W0QQitemZ200146194738QQihZ010QQcategoryZ30922QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Edit - check Haynes or Porter for the correct gap rather than take my word for it, I'm not 100% sure it should be 0.7mm.

 

[Plug]

Right, then..

From what I remember from my physics days (many years ago now) it takes a potential difference of about 100,000 volts/cm to create a spark in air. Scale that to 0.7mm assuming Steven is there or thereabouts with his plug gap, you're looking at a PD of 7000 volts to arc across the plug. This seems reasonable, I've had a belt or two off an HT coil in my time - cars and CRT monitors have both played their part in this - and they both hurt pretty much the same.

Consider that the coil packs on your car are 13 years old, they may not be performing as new and the plug gap may be more critical. I've no idea what the tolerance on them is as I'm more used to dealing with low voltage systems (as stated above, HT hurts and I don't enjoy pain.. ).

On the other hand, I may be talking out of my posterior, in which case feel free to disregard my wafflings..

Cheers,

Plug