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Why do some spark plugs have a screw-on contact terminal?

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Doc

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Nov 22, 2012, 9:46:10 PM11/22/12
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The subject mostly says it. Why do some plugs have these terminals
that screw on as opposed to a solid piece?

Steve W.

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Nov 23, 2012, 12:10:33 AM11/23/12
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Doc wrote:
> The subject mostly says it. Why do some plugs have these terminals
> that screw on as opposed to a solid piece?

Because they are also used in applications that use the threaded stud as
the contact. Many snowmobile and military engines use the threads to
retain the wire. Keeps the wire on regardless of vibration.

--
Steve W.

m6onz5a

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Nov 23, 2012, 9:43:16 AM11/23/12
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On Nov 22, 9:46 pm, Doc <docsavag...@yahoo.com> wrote:
> The subject mostly says it. Why do some plugs have these terminals
> that screw on as opposed to a solid piece?

small engines use them.

Tegger

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Nov 23, 2012, 12:33:36 PM11/23/12
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Doc <docsa...@yahoo.com> wrote in news:9dd9d43a-b2c7-4378-a717-
c1b018...@b6g2000yqd.googlegroups.com:

> The subject mostly says it. Why do some plugs have these terminals
> that screw on as opposed to a solid piece?



For the reasons given by others. Very old cars (Ford Model-T, for instance)
also used this type.

I've been told not to use the screw-top types on modern automobile engines.
If the screw tops happen to be loose (or come loose), they can cause arcing
and ignition problems.

--
Tegger

jim beam

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Nov 23, 2012, 2:19:46 PM11/23/12
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yeah in theory, but in reality, they cause more reliability problems
than they solve. screw-on terminals aren't typically weather sealed in
the way that push-on terminals can be. and the threads themselves can
be problematic too. when trying to use a push-on over a screw cap [as
is typically the case with modern applications], if the cap isn't
absolutely tight, there can be sparking and erosion under the threads
causing all kinds of intermittent misfires that are otherwise hard to
diagnose. to make matters worse, caps have a nasty habit of loosening
over time [thermal cycling] and what may once have been "fixed" can soon
become a problem again.

bottom line, i won't use them - only one-piece capped plugs for me.


--
fact check required

JR

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Dec 3, 2012, 10:22:21 AM12/3/12
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Use jam nuts on them and they won 't lossen. My 1914 Model T Ford car has the old style spark plugs. The spark plugs also can be easily disassembled with two wrenches for easy cleaning.
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