Viewing a thread - 56 single rocker 315 spark plugs

You are logged in as a guest. ( logon | register )

56 single rocker 315 spark plugs Jump to page : 1 Now viewing page 1 [50 messages per page]	View previous thread :: View next thread
Forward Look Technical Discussions -> Engine, Exhaust, Fuel and Ignition	Message format

dels56

Posted 2025-07-29 3:50 PM (#641023)
Subject: 56 single rocker 315 spark plugs

Extreme Veteran

Posts: 457
100

Can anyone confirm the O.E. spark plug mfg/ number of the spark plugs in a 56 U.S. built Custom Royal with the 315 cube single rocker (semi hemi)?

The Field Service Manual list AR52 Autolite, 14mm, 3/4” reach. These are totally wrong. The engine takes a 14mm, 3/8” reach plug. 56D500boy’s (Dave’s) Hemi also take a 3/8” reach plug.

I cannot find the number for the original plugs in any service manual, parts book or on the internet. Your help will be appreciated.

Del

JedRhule

Posted 2025-07-29 5:33 PM (#641024 - in reply to #641023)
Subject: Re: 56 single rocker 315 spark plugs

Veteran

Posts: 130
100

Location: Palm Beach County Florida

I am using Champion RJ18YC. I like the shiny look of the Champion. I am running .045 gap with my Pertronix. Three years and 2000 miles they are burning clean.

dels56

Posted 2025-07-29 6:51 PM (#641027 - in reply to #641023)
Subject: Re: 56 single rocker 315 spark plugs

Extreme Veteran

Posts: 457
100

Thanks Jed. I am running the 0.035” gap with Pertronix. I’m wondering what difference it makes? What advance do you run?

Del

JedRhule

Posted 2025-07-29 7:05 PM (#641028 - in reply to #641023)
Subject: Re: 56 single rocker 315 spark plugs

Veteran

Posts: 130
100

Location: Palm Beach County Florida

I replaced the vacuum advance and advance springs when I installed the Pertronix. I am running 35 degrees total advance at 2500 RPM. She pulls nice in high gear without having to dump the throttle to low gear. Even though I cleaned the oil drains from the head, sometimes I get a little oil smoke from the right back when I first start up. I am hoping the .045 spark will burn off the oil.

dels56

Posted 2025-07-29 7:22 PM (#641029 - in reply to #641023)
Subject: Re: 56 single rocker 315 spark plugs

Extreme Veteran

Posts: 457
100

Thanks Jed, i am going to try NGK XR4. My old gal runs like a switch watch, where I live in B.C. it is very hilly and I can gain speed on most grades.

Del

56D500boy

Posted 2025-07-29 7:52 PM (#641030 - in reply to #641023)
Subject: RE: 56 single rocker 315 spark plugs

Exner Expert 10K+

Posts: 10992
5000

Location: Lower Mainland BC

.
Del: On page 519 of the 56 Dodge FSM, it list the spark plug as a 14 mm AutoLite AR-52 plug. No mention of reach. I am not sure
where/why you have seen info that says the AR-52 is a 3/4" reach. It is not. Or at least it wasn't in 1956.

(NOTE: That said, the factory information sometimes screws up and gets confused so mention of a 3/4" reach might be possible)

However, this is the info that I have used in the past to guide me to the selection of plugs for my 56 315 double-rocker.

Discussion of reach for the 58 Dodge Engines:

One conversion chart (which translates an AR-52 to a AC Delco R45S or a Champion J-18Y (all 3/8" reach)

Apparently old AutoLite AR-52s now translate to AutoLite 86 plugs.

https://www.amazon.ca/Autolite-86-Copper-Resistor-Spark/dp/B000CIHNL...

Edited by 56D500boy 2025-07-29 7:54 PM

56D500boy

Posted 2025-07-30 2:46 AM (#641033 - in reply to #641030)
Subject: RE: 56 single rocker 315 spark plugs

Exner Expert 10K+

Posts: 10992
5000

Location: Lower Mainland BC

.
Del: I hope that we can prevent you from making a mistake and installing 3/4" reach plugs in your 315 poly.

That old school NOS AR52 photo I posted above clearly shows that the plug has a 3/8" reach.

From the Conversion table that I posted above, the Autolite AR52 crosses to a Champion J18Y like this one:

https://www.ebay.ca/itm/255937375891

I dug out my alternative 56 Mopar Parts Catalog and in that, in Section 8, Electrical, Sub-section 37, Spark plugs, for all 56 V8s,
with 2 exceptions, it calls for the AR52. The exceptions are a Desoto that wants and AR-82 and big Chrysler (likely the 354 hemi) that wants an
AGR-42. (NOTE: The catalog came out BEFORE the D500 315 hemi was announced so it is not included in the list of exceptions to the AR-52 rule)

From the table above the AR-82 is also a 3/8" reach plug.

I found an AR-82 on eBay, definitely 3/8" reach.

https://www.ebay.ca/itm/374950089083?

Found an AGR-42 (actually 10 of them) on eBay (this one is definitely 3/4", the only one in this game, all the rest are 3/8" reach)

https://www.ebay.ca/itm/363512808292

Images from the 56 Parts Catalog:

Edited by 56D500boy 2025-07-30 2:52 AM

(56MoparPartsBook_Cover_1024.jpg)

(56MoparPartsBookPg31_ElectricalSections_1024.jpg)

(56MoparPartsBook_SparkPlugs_1024.jpg)

Attachments
----------------

56MoparPartsBook_Cover_1024.jpg (148KB - 207 downloads)
Attachments

56MoparPartsBookPg31_ElectricalSections_1024.jpg (145KB - 208 downloads)
Attachments

56MoparPartsBook_SparkPlugs_1024.jpg (149KB - 186 downloads)

dels56

Posted 2025-07-30 10:51 AM (#641036 - in reply to #641023)
Subject: Re: 56 single rocker 315 spark plugs

Extreme Veteran

Posts: 457
100

I have always liked NGK plugs, I picked up a set of XR4, 14mm, 3/8” reach from our local Auto Parts Store which I had cross referenced from all the info I received. I contacted NGK, a live tech person, to confirm the heat range prior to installing them. I will run these for a while, then check to see how they are burning. Thanks for all the info. I do catalog a lot of what the info.

Del

Jump to page : 1
Now viewing page 1 [50 messages per page]

Jump to forum :

Search this forum
Printer friendly version
E-mail a link to this thread

* * * This site contains affiliate links for which we may be compensated * * *

(Delete all cookies set by this site)