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Old 01-23-2008, 09:13 PM
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5/8th spark plug replacement for 13/16 rj12 yc

i have been use rj12 yc champions in my 440 for 10 years. they have the 13/16" base. is there a replacement 5/8ths mini plug recommended for header apps?

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Last edited by spinn; 01-24-2008 at 04:11 PM.
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Old 01-23-2008, 09:38 PM
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Wouldn't the threads be different?

Shane
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Old 01-23-2008, 09:42 PM
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no , 5/8th meaning the socket required to remove it.

a 5/8" socket is easier to manuver around headers than a 13/16"
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Old 01-23-2008, 09:44 PM
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Are you talking about a 440 Mopar? With long reach threads and a washer for sealing? Hmmmm, tough question for me. I think i've seen some long reach 5/8" washer type plugs, but have no idea what heat range they'd be. Threads will be the same, unless you have a 440 Ford! LOL

Mark
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Old 01-23-2008, 10:07 PM
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Quote:
Originally Posted by spinn
no , 5/8th meaning the socket required to remove it.

a 5/8" socket is easier to manuver around headers than a 13/16"
Yeah,But arent the threads different sizes,but I am assuming your looking for a retrofit plug,If you cant find one just shave it down to 5/8ths

Shane
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Old 01-23-2008, 10:15 PM
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Unless it's a big Ford plug, the threads will be the same, they are all metric anyways! (atleast that's what I recall, but I am getting older!)

Mark
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Old 01-23-2008, 10:32 PM
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Quote:
Originally Posted by Chevrolet4x4s
Yeah,But arent the threads different sizes,but I am assuming your looking for a retrofit plug,If you cant find one just shave it down to 5/8ths

Shane

dont tempt me, man... i got a lathe, and know how to use it.

the best smallblock head plug for me was the autolite 3929 tiny for those crazy fit headers.
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Old 01-23-2008, 10:52 PM
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Could probabally mill a batch down quicker than you could find a set,also have you seen the sloted header plug sockets they have out now?

Shane
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Old 01-24-2008, 05:16 AM
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A Sparkplug with 13/16" hex is usually an 18mm thread......

A Sparkplug with a 5/8" hex is usually a 14mm thread.......
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Old 01-24-2008, 07:47 AM
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Quote:
Originally Posted by bondo
A Spark plug with 13/16" hex is usually an 18mm thread......

A Spark plug with a 5/8" hex is usually a 14mm thread.......
There is a lot of 14mm thread plugs with 13/16th hex sizes. early Chevy's, Buicks, Pontiacs, cadilacs, Mopar's and allot of early foreign cars had the 14mm with 13/16" hex sizes. Even older Briggs and Stratton etc.

gcrmcc
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Old 01-24-2008, 03:53 PM
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okay "the grape vine" say bosch platiumun HR 8 BPX have the 5/8 mni "header plug" design.

anybody cobfirm this?
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Old 01-24-2008, 03:58 PM
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Generally, the 5/8 plugs have the tapered seal, whereas the 13/16 had the flat spot and a washer. Find the right heat range and it would probably seal OK....
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Old 01-24-2008, 07:24 PM
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Check into NGK. I know for SBC aftermarket heads such as Brodix and AFR that NGK has the plugs available in both 5/8 and 13/16 heads that are 14mm x .750 gasket style.
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Old 01-25-2008, 06:36 AM
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You need to decode the plugs you are running now and try to find another that has all the same attributes with the exception of the socket size. Any plug manual will be able to give you the heat range, reach etc.
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Old 01-25-2008, 07:15 AM
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My $.02 ------
Yesterday , i tried to get some plugs that were one range hotter than the CR45 ( A/C Delco ) plugs I normally use. The 46's had a 13/16th socket size and the 45's are 5/8" .....
the 13/16th's wouldn't thread in .
I returned them for some good ol' 45's .
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