What's the deal with Delco Spark Plugs? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**71CHEVYSHORTBED402** · 03-04-2019, 09:02 PM

71 C-10 402

Getting around to replacing the spark plugs on the project, and have to ask, how can spark plugs be difficult?...............EDIT, Because, I forgot my heads are off a late 60s HP 396The rest is nonsense.......

I picked up Delco R44T from Napa, and checked out the part number, but I can't start the threads. The old plugs (Autolite) and the Delco are a 9/16" fine thread 18, but if anything the old threads are cleaner. They install with ease, and no issues since originally installed, 15-20 years ago.

Delco is a shorter thread and doesn't take a lock washer I guess. I don't recall seeing them without one, but I suppose they work - assuming you can install them to begin with

So what the heck? Possible the Autolite compromised the threads in the heads somehow? I've installed 3-4 sets of new plugs since I've owned her, never a problem.

Edit: Interesting. AP 404 Autolite doesn't cross reference to R44T, same vise versa. Something is peculiar. Ah SNAP!, I just remembered my heads are HP off a late 60's Corvette or Camaro. I wouldn't expect so, but that's got to be it.

weq92f · 03-04-2019, 09:35 PM

.
The difference is the date of manufacture of the head. Earlier heads, prior to 70 I believe, have the straight threads with the washer. Later heads have the newer style threads which do the sealing themselves.

If you select plugs for a 68 Chevrolet Camaro SS w/396, you'll get the right ones!

-klb

**Grumpy old man** · 03-04-2019, 09:40 PM

Two different spark plugs for two different style heads .

**Steeveedee** · 03-04-2019, 09:43 PM

I deleted my previous post after looking at you old plugs again. You did not get the correct plugs from the parts store. Those are for a SBC, which I believe did have tapered seat plugs in 1970. You need plugs with the 3/4" "N" designation reach, and not tapered seats, but the compressible washer like on the old plugs.

**71CHEVYSHORTBED402** · 03-04-2019, 09:44 PM

BINGO!..................Ha, I used to know that

...Been so long since I replaced the spark plugs. And I'm getting old

tdangle · 03-05-2019, 05:56 PM

Earlier heads used a flat surface with a washer on the plug. AC plugs are numbered such example R44T is resister plug 44 heat range T designates flat sealing surface with washer

R44ts as used in later heads R is resister 44 is heat range and the ts is taped seat

Correct me if I'm wrong.

RichardJ · 03-05-2019, 10:10 PM

oy vey !

**71CHEVYSHORTBED402** · 03-05-2019, 11:58 PM

Quote:

Originally Posted by RichardJ

oy vey !

So much for the idea they're 9/16"-18 threads. Pretty close I guess

tdangle · 03-06-2019, 01:15 AM

Quote:

Originally Posted by RichardJ

oy vey !

Thanks for the info. Never too old to learn

burnin oil · 03-07-2019, 02:22 AM

Now have fun and go to Autolites web page and try and figure out their nightmare. Especially when it comes to crossing regular plugs with the race applications.

cleszkie · 03-07-2019, 09:38 PM

A cross thread provides the best seal possible

I'd keep trying with the wrong plugs until they catch. Then crank 'em in with a cheater bar!

**zicc1835** · 03-07-2019, 10:07 PM

Quote:

Originally Posted by cleszkie

A cross thread provides the best seal possible

I'd keep trying with the wrong plugs until they catch. Then crank 'em in with a cheater bar!

ruff crowd

**71CHEVYSHORTBED402** · 03-08-2019, 01:12 PM

Quote:

Originally Posted by cleszkie

A cross thread provides the best seal possible

I'd keep trying with the wrong plugs until they catch. Then crank 'em in with a cheater bar!

Couldn't get em to start, even after taking a sledge hammer to them. Thought I had em, but the plugs just break in half. I may try some epoxy

**DeadheadNM** · 03-08-2019, 10:09 PM

Now that’s solved what’s the deal with AC Delco making plugs in China

palallin · 03-08-2019, 11:54 PM

Drill out the holes, shove the plugs in, and weld those puppies in place!

**71CHEVYSHORTBED402** · 03-09-2019, 12:18 AM

Quote:

Originally Posted by palallin

Drill out the holes, shove the plugs in, and weld those puppies in place!

Was thinking that - right after I mentioned epoxy, ha ha, imagine if you didn't do it right

A weld is permanent

03-04-2019, 09:02 PM	#1
71CHEVYSHORTBED402 Senior Member Join Date: Feb 2009 Location: Northern Nevada Posts: 7,274	What's the deal with Delco Spark Plugs? 71 C-10 402 Getting around to replacing the spark plugs on the project, and have to ask, how can spark plugs be difficult?...............EDIT, Because, I forgot my heads are off a late 60s HP 396The rest is nonsense....... I picked up Delco R44T from Napa, and checked out the part number, but I can't start the threads. The old plugs (Autolite) and the Delco are a 9/16" fine thread 18, but if anything the old threads are cleaner. They install with ease, and no issues since originally installed, 15-20 years ago. Delco is a shorter thread and doesn't take a lock washer I guess. I don't recall seeing them without one, but I suppose they work - assuming you can install them to begin with So what the heck? Possible the Autolite compromised the threads in the heads somehow? I've installed 3-4 sets of new plugs since I've owned her, never a problem. Edit: Interesting. AP 404 Autolite doesn't cross reference to R44T, same vise versa. Something is peculiar. Ah SNAP!, I just remembered my heads are HP off a late 60's Corvette or Camaro. I wouldn't expect so, but that's got to be it. Attached Images __________________ Tony 71 Custom Deluxe, SWB, 2WD, 402, A/C. I developed an assembly kit for restoring the (a) truck from the ground up. My build thread, and more on the assembly kit https://67-72chevytrucks.com/vboard/...d.php?t=730025 Last edited by 71CHEVYSHORTBED402; 03-05-2019 at 01:36 AM. Reason: Oooooooooops. Left for entertainment "value".

03-04-2019, 09:35 PM	#2
weq92f Registered User Join Date: Oct 2016 Location: Dallas Texas Posts: 3,118	Re: What's the deal with Delco Spark Plugs? . The difference is the date of manufacture of the head. Earlier heads, prior to 70 I believe, have the straight threads with the washer. Later heads have the newer style threads which do the sealing themselves. If you select plugs for a 68 Chevrolet Camaro SS w/396, you'll get the right ones! -klb __________________ 67 C10 fleet fuel injected '70 402, 700r4, 3.73 posi 07 335 sport turbo 6sp 94 Trans Am GT LT1 6sp posi -- sold after 22yrs 99 540 sport V8 6sp -- sold 73 240z L24 4sp -- given to friend 68 C10 step 350/350 3.73 open -- sold

03-04-2019, 09:40 PM	#3
Grumpy old man Senior Member Join Date: Dec 2013 Location: Gods country East,Tn Posts: 8,545	Re: What's the deal with Delco Spark Plugs? Two different spark plugs for two different style heads . __________________ 1967 Factory short bed - Old school '71 - 350 / 4bolt / 487 heads / Edelbrock C3BX Muncie M-22 4 speed / Hurst Comp plus Factory 12 bolt posi 3.73 / 255-70-15 Smoothed firewall / Factory cowl induction Power disc brakes / power steering / 3.5-5" drop

03-04-2019, 09:43 PM	#4
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,527	Re: What's the deal with Delco Spark Plugs? I deleted my previous post after looking at you old plugs again. You did not get the correct plugs from the parts store. Those are for a SBC, which I believe did have tapered seat plugs in 1970. You need plugs with the 3/4" "N" designation reach, and not tapered seats, but the compressible washer like on the old plugs. __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA

03-04-2019, 09:44 PM	#5
71CHEVYSHORTBED402 Senior Member Join Date: Feb 2009 Location: Northern Nevada Posts: 7,274	Re: What's the deal with Delco Spark Plugs? BINGO!..................Ha, I used to know that...Been so long since I replaced the spark plugs. And I'm getting old __________________ Tony 71 Custom Deluxe, SWB, 2WD, 402, A/C. I developed an assembly kit for restoring the (a) truck from the ground up. My build thread, and more on the assembly kit https://67-72chevytrucks.com/vboard/...d.php?t=730025

03-05-2019, 05:56 PM	#6
tdangle Registered User Join Date: Mar 2005 Location: Jurupa Valley, Ca Posts: 1,210	Re: What's the deal with Delco Spark Plugs? Earlier heads used a flat surface with a washer on the plug. AC plugs are numbered such example R44T is resister plug 44 heat range T designates flat sealing surface with washer R44ts as used in later heads R is resister 44 is heat range and the ts is taped seat Correct me if I'm wrong. __________________ Terry 1970 Custom Camper/C20 , GM Crate 350/7004R, Dana 60, factory AC

03-05-2019, 10:10 PM	#7
RichardJ Registered User Join Date: Apr 2010 Location: So Cal Posts: 1,451	Re: What's the deal with Delco Spark Plugs? oy vey ! Attached Images __________________ '67 GMC 2500, 292, 4spd, AC

03-07-2019, 02:22 AM	#10
burnin oil Registered User Join Date: Jan 2013 Location: Eastern TN Posts: 1,921	Re: What's the deal with Delco Spark Plugs? Now have fun and go to Autolites web page and try and figure out their nightmare. Especially when it comes to crossing regular plugs with the race applications.

03-07-2019, 09:38 PM	#11
cleszkie Registered User Join Date: Feb 2003 Location: Santa Ana, CA Posts: 2,191	Re: What's the deal with Delco Spark Plugs? A cross thread provides the best seal possible I'd keep trying with the wrong plugs until they catch. Then crank 'em in with a cheater bar!

03-08-2019, 10:09 PM	#14
DeadheadNM Carpe manana Join Date: Dec 2010 Location: Eau Claire, WI Posts: 12,414	Re: What's the deal with Delco Spark Plugs? Now that’s solved what’s the deal with AC Delco making plugs in China Attached Images __________________ 1972 K5 CST Highlander Blazer: http://67-72chevytrucks.com/vboard/s...d.php?t=708547 1972 K20 Cheyenne Super: http://67-72chevytrucks.com/vboard/s...d.php?t=528308 Members met: ORANGBLAZ, 2003 silverado, MikeCofield, BB72CHEVKT, Duncan&Son, Sameyrasmea72, THENEWMEXICAN, HotRod C/10, brianthelion02, Sport/Truck, ryanroo, michael bustamante, Dirt's72, Already Gone, WestButteTruck, 57taskforce, Moreyel, painterljp, AASmedic, SoCoC10, Lumaestas, carbuff382, Chevyland

03-08-2019, 11:54 PM	#15
palallin Registered User Join Date: Jul 2002 Location: St. James, MO Posts: 1,239	Re: What's the deal with Delco Spark Plugs? Drill out the holes, shove the plugs in, and weld those puppies in place! __________________ '69 Longstep K-10: 327/SM465/T-221/Closed Knuckle Dana44/12-bolt.



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