Finally got around to replacing the plugs

Only I broke the rules and changed 4 things at once so I don't know what made the improvement........


The 4 things were:

1. Autolite extended tip 985 plugs
2. .044 gap
3. cutoff electrode so end was only over 1/2 of center electrode
4. (semi)-indexed the plugs. (went thru 12 plugs to get 2 sets where the side electrodes would be in the upper section of the combustion chamber - best fit for all 6 plugs, not necessarilly best for individual cylinder)

see:
http://www.slantsix.org/forum/viewtopic.php?t=21933

for my comment on slant 6 indexing and indexer tool.....

_________________
Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

How did it change the idle? In my experiene just extended tip plugs made things better by quite a bit. Tell us the theory behind cutting the electrode back.

Sam

_________________

The idea of the cut back electrode is to expose more of the spark to the combustion chamber.. see:

http://www.sparkplugs.com/sparkplug411. ... und&mfid=0


As for the idle, with the standard plugs, I had what was essentially a random misfire. Maybe once or twice a minute (might extend to once every couple of minutes) there was a miss, felt it more than heard it.

_________________
Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

The idea is to "unshroud" the spark so that the fuel/air mixture in the combustion chamber has greater exposure to the spark. NGK spark plugs come with a V-notched centre electrode which accomplishes the same goal, though I suppose one could cut back the side electrode of an NGK "V-Power" spark plug to further unshroud the spark. The tradeoff of this modification is reduced spark plug electrode life. If you do this (to any spark plug), take care not to create a sharp ridge at the lower inside edge of the side electrode, which would foil attempts to check and set the gap correctly.

Trivia: It's known as "J-gapping", probably because Champion's numbering system used to assign a "J" suffix to spark plugs that come this way from the factory, primarily those intended for use in small air-cooled engines, where such plugs are more resistant to "bridge fouling" that occurred with older gasoline formulations under some conditions.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

I tend to "J" gap the plugs that go into race engines... quick & easy unshrouding with-out snipping or grinding.

On the topic of plugs...
You don't want to unshroud the spark by leaning the center electrode over to one side!



http://www.dutra.org/pictures/engine/plugs.jpg

Last time out at the track, I put a new set of Autolites into the engine and picked-up a miss. After a bunch of trouble-shooting (and lost rounds) I found a defective spark plug. At first I thought something had gone thru that cylinder and hit the plug's center electrode but upon close inspection, the plug came out of the box that way. If it was not for this plug running "darker" then the others, (misfiring) It would have taken even longer to see the defect.

Needless to say... I am looking closer at new plugs as they come out of their boxes.
DD