Why spark plugs fail?
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Topic author - Posts: 6496
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Why spark plugs fail?
This morning I was asked this question: "What would cause a plug to NOT fire under compression?"
I know one reason, but there are others. What do you think?
I know one reason, but there are others. What do you think?
The inevitable often happens.
1915 Runabout
1923 Touring
1915 Runabout
1923 Touring
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Re: Why spark plugs fail?
Often, carbon will build up, or a film of gas/oil, and the plug will spark between the base and the insulator, not across the gap...
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Re: Why spark plugs fail?
I wondered why my Grandfather had several T plugs he kept along with a box of coils. They all looked to be pretty good. After having the T he gave me over 50 years ago and the boxes of extra parts that came along with it I’ve come to the conclusion he wasent the first and certainly not the last to have an extra part or two to interchange when the T didn’t seem to run right.
I still do the same thing. It’s just the nature of the T I guess.
I still do the same thing. It’s just the nature of the T I guess.
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Re: Why spark plugs fail?
Plugs do get worn out. Even cleaning them only works for a short while till they need to be redone. The spark likes to jump from a sharp edge and when that edge gets rounded over, not so much.
I know the voices aren't real but damn they have some good ideas!
1925 Cut down pickup
1920 Dodge touring
1948 Ford F2 pickup
1925 Cut down pickup
1920 Dodge touring
1948 Ford F2 pickup
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Re: Why spark plugs fail?
Common causes:
Fouled with oil or carbon
Gap incorrect (too small / too great) for ignition type / source /cylinder compression
Excess heat, deforms electrodes, metallic particles affixed due to heat
Deformed electrodes from current wear over time
Cracked porcelain, due to heat or trauma, causes short circuit
Un-common:
Broken center electrode from pliers used to tighten the plug wire
Champion 25 uses an adhesive fixed upper for the center electrode.
Best to always tighten spark wires with only finger and thumb, holding the plug thumb nut as you rotate the wire terminal snug.
Fouled with oil or carbon
Gap incorrect (too small / too great) for ignition type / source /cylinder compression
Excess heat, deforms electrodes, metallic particles affixed due to heat
Deformed electrodes from current wear over time
Cracked porcelain, due to heat or trauma, causes short circuit
Un-common:
Broken center electrode from pliers used to tighten the plug wire
Champion 25 uses an adhesive fixed upper for the center electrode.
Best to always tighten spark wires with only finger and thumb, holding the plug thumb nut as you rotate the wire terminal snug.
The best way is always the simplest. The attics of the world are cluttered up with complicated failures. Henry Ford
Don’t find fault, find a remedy; anybody can complain. Henry Ford
Don’t find fault, find a remedy; anybody can complain. Henry Ford
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Re: Why spark plugs fail?
And that is why I do not use those 25's, been there done that.^
I know the voices aren't real but damn they have some good ideas!
1925 Cut down pickup
1920 Dodge touring
1948 Ford F2 pickup
1925 Cut down pickup
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1948 Ford F2 pickup
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Re: Why spark plugs fail?
" spark likes to jump from a sharp edge and when that edge gets rounded over, not so much."
Mark, since both electrodes on the old brass-top Champions are made of round wire, would the sharp edge be only where the base (grounded) electrode is sheared off ? It's easy to note the "wear" (erosion) on spark plug electrodes, would it help to dress the edge of the ground electrodes as they become "dubbed" with use ?
Mark, since both electrodes on the old brass-top Champions are made of round wire, would the sharp edge be only where the base (grounded) electrode is sheared off ? It's easy to note the "wear" (erosion) on spark plug electrodes, would it help to dress the edge of the ground electrodes as they become "dubbed" with use ?
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Re: Why spark plugs fail?
I have had spark plugs fail from being flooded with gas. No amount of drying or heating would make them fire properly again.
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Re: Why spark plugs fail?
I had an annoying skip while under load that drove me crazy for weeks. After checking all the usual suspects, wiring, timing, etc.., i decided to pull all the plugs apart and found this. Although i couldn't visually detect a crack in the porcelain, there was some definite carbon tracking going on. Replaced the plug with a spare i had, and the skip was gone. You never know how little things like this can make your T run, but then again, that's part of the fun of this hobby.
Experience is a wonderful thing. It enables you to recognize a mistake when you make it again.
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Re: Why spark plugs fail?
Re"Mark, since both electrodes on the old brass-top Champions are made of round wire, would the sharp edge be only where the base (grounded) electrode is sheared off ? It's easy to note the "wear" (erosion) on spark plug electrodes, would it help to dress the edge of the ground electrodes as they become "dubbed" with use ?"
That is what I have read in the past. So I am going to say yes, the spark wants to jump from the sheared sharp edge. You can only sharpen the edges so many times.
That is what I have read in the past. So I am going to say yes, the spark wants to jump from the sheared sharp edge. You can only sharpen the edges so many times.
I know the voices aren't real but damn they have some good ideas!
1925 Cut down pickup
1920 Dodge touring
1948 Ford F2 pickup
1925 Cut down pickup
1920 Dodge touring
1948 Ford F2 pickup