[T3] Spark plug gap

[Jim Adney]

On 2 Jul 2016 at 16:53, 73 squareback Cincy wrote:

> looks like its .024 in the bently manual.

I'm sure .024 works, but I usually go to .027, mostly because that's 
one of the settings on my gapper and that opens up the gap a bit and 
also seems to work. If the gap gets TOO big, the spark will find 
other places to jump and you'll get misses. If the electrode corners 
aren't too rounded, it's often acceptable to just re-gap the plug and 
re-use it. I know that the plug makers say you have to replace the 
gasket/washer, but I've never found that to be necessary.

It took me decades to understand what constituted a worn out spark 
plug. Look at the center electrode: When new, it's corners are 
square, which means very large electric field which breaks down 
easily (sparks easily). As the plug is used, the corners wear away 
and get rounded; Eventually the corners get so round that the spark 
won't form and jump the gap. Then the engine starts to miss. That's 
the time to replace the plug.

If the insulator looks to be the wrong color, that's usually not a 
reason to replace the plug; that's a reason to look at your mixture 
(carbs or FI) or consider using a different heat range plug.

Of course, if the insulator is broken, you'll need to replace the 
plug, but you also need to figure out WHY the insulator broke and fix 
that root cause. For the record, the only cracked insulator I've ever 
seen was on my snow blower, when I heated the plug with a torch to 
clean it off and heated the insulator too abruptly.

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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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