Hi
My Escort has an HCS engine with carburettor. The specified spark plug gap is 1.0mm. However, when the garage fitted new plugs (champion copper core/electrode), they didn't adjust their gap and left them at 0.8mm. Being as this didn't affect performance, I though I'd leave it as that. However, I've just had a rethink, and was wondering if there is any damage being done to the coils in terms of increased current?
Any thoughts?
Thanks
Mike Farrow
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Mike,
I would think minimal damage will be occurring to the coils. High voltage electrical kit tends to fail after either physical damage, overheating*, water damage, or fatigue failure, with peak voltage playing the analagous role to peak stress in the fatigue of mechanical systems. Reducing the plug gap, providing it doesn't send the HCs up is not a bad thing to do, to reduce 'stress' on the ignition system.
* Since the demise of contact breaker points, coil overheating failures are much rarer.
number_cruncher
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Lazy garage! If the recommended gap is 1.0mm (32 thou)I would set the plugs to that. A narrower gap promotes spark erosion.
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0.8 mm can and will cause slightly premature and weak arc as the HT has not risen far enough before it leaps across the normally controlled gap. This will infact cause misfire, particularly under higher speed higher load conditions where you may not detect it. 1mm is in fact 40 (39.37) thou and that you should use. Regards Peter
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Peter,
I agree in all but pedantry. You say 'it will cause misfire', I would say 'it may cause misfire', which is why I mentioned HCs in my earlier post.
Rather than the peak HT voltage being important, I view the spark energy and burn time as the important things.
Setting the plugs to the recommended gap is, of course, a reasonable thing to do - just not something to loose sleep over!
number_cruncher
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NC. In theory you may be right. But in practice it doesnt work out..In most cases of plug gap not being correct usualy causes problems. Maybe not straight away but later in the plugs life..As Peter mentioned. It happens a lot..Ps isnt the gap designed to give max spark at peak HT.Surely if this wasnt the case a specified gap would not be needed?
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Steve
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Hi Steve,
If you set the gap *way* too small then you get misfire problems, especially if the engine runs very weak, or is very turbulent near the plug. (Which the HCS engine may be?)
If you set the gap *way* too big, you get misfires because the spark finds another way out.
Some engines are really sensitive to running with narrowed gaps - particularly BMW six cylinder engines for some reason. Others aren't too picky, Vauxhall 8 valve engines for example - with minimal combustion chamber changes, these engines have gone from points to wasted spark four pronged plugs over the years.
Obviously, as soon as use the engine, the plug gap is changing!
number_cruncher
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You have only told me what I know already..Except you mean excessive gaps..I think point made was gap is not to spec should it be so..Simple answer is yes.AS for plug gap changing whilst using the engine..Unlikely gap will change by anymore than a micron or two/probably less
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Steve
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Steve,
We are in broad agreement here. We are only disagreeing over the importance.
The original poster says the car is running well. My experience of this issue is that the car will probably continue to run well.
Therefore, I think it is unlikey to become a show stopper, and this (at least) 11 year old car is likely to have more important 'issues' elsewhere.
As I said above, setting the gap correctly is a sensible thing to do, but I still say not to loose sleep over it.
number_cruncher
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I dont agree with your post..NC.Your point was made..Also see other point made..Tend to think you missed the point..Its all very well knowing the reasons why certain things happen. But would suggest your point made in laymans terms.. few people out there know technical terms as you put it..I have no wish to insult your intelligence but think on some occasions laymans terms will help rather than HI teck. As some will not understand. I stress the point.. not having a go please relate to those that dont have a clue. many out there dont..Sorry if I offended. Have no wish to..
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Steve
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Peter D, I meant to type 39 thou instead of 32 but you are quite correct that its actually 39.37 thou.
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Steve,
Thank you for your kind stylistic feedback. Thankfully, I haven't taken offence.
However, please don't be offended if I choose to ignore your style advice.
While I hope that I write intelligible English, it is possible that some people may have difficulty from time to time. If so, I am happy to discuss further any source of confusion, as and when it happens; this relies on the correspondent asking intelligent and articulate questions where necessary; something at which most users of this forum shine.
It is a healthy state of affairs for us to disagree on small issues occaisonally - it needn't be a source of friction, because neither of us can be or will be right (or wrong) all of the time.
number_cruncher
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Hi
I seem to have started quite a debate!
Thanks to everyone who replied. I will change the plug gap when I next fiddle, probably the January oil change. I would have changed the gap in July if it had been for one Haynes manual saying 0.8mm, and another (for Orion) saying 1.0mm (I'm reading the HCS sections not for older OHV, in case you ask).
As I've said before the engine runs fine at the lower gap, and when the garage changed the plugs (which I'd only fitted and gapped to 1.0mm 6 months previous {snarl}) I didn't notice any difference, not even on motorways which I thought you would have in a car with 4 gears (that's 10mph per 500rpm in 4th).
I hope coking won't be an issue, as I use Redex, though mainly for prolonging bore life as it only travels 1/2 mile every day! Anyhow I don't want to start the "is Redex any good?" argument again!
Thanks again!
Mike Farrow
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Getting back to Plug gaps..I noticed today going to local motor factors. Not for plugs though. A chap was filling up a plug bin.
And was surprised to notice the plug box was thrown across the the floor toward the bin..Can see why so many plug failures and incorrectly gapped plugs.
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Steve
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Well, Got to agree with NC here. The plug gap is nominal in the same way a 12v battery is. A couple of volts higher (or lower on starting) or a few thou. either side won't make that much difference.
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