Replacement Spark Plug Questions...

[bamfordsgarage]

I'm replacing the spark plugs in my 1947 D25. No particular reason other than old age and I'm chasing a bit of a mis-fire. The current plugs are 10+ years and many thousand miles old. Most of my driving is lower speeds and shorter trips with occasional longer runs at 50-55 mph (had a 600-mile weekend February). I run no on-board electronics other than an iPhone.

 

The P15-D24 Resources page lists a variety of spark plugs; none are stocked at NAPA and most come up as a different number/manufacturer anyway. 

 

NAPA recommends, and stocks, an Autolite 306 Resistor plug for the 1947 P15. 

 

• Should I avoid a resistor plug given my lack of electronics and the (I assume) advantages of a stronger spark?

 

• Are there potentially better plugs (heat range, manufacturer, etc) to consider given my driving conditions?

 

Spark plugs with all their myriad of variations have been largely a mystery to me. Your wisdom and experience will be much appreciated!

 

 

[harmony]

1 hour ago, bamfordsgarage said:

I'm replacing the spark plugs in my 1947 D25. No particular reason other than old age and I'm chasing a bit of a mis-fire. The current plugs are 10+ years and many thousand miles old. Most of my driving is lower speeds and shorter trips with occasional longer runs at 50-55 mph (had a 600-mile weekend February). I run no on-board electronics other than an iPhone.

 

The P15-D24 Resources page lists a variety of spark plugs; none are stocked at NAPA and most come up as a different number/manufacturer anyway. 

 

NAPA recommends, and stocks, an Autolite 306 Resistor plug for the 1947 P15. 

 

• Should I avoid a resistor plug given my lack of electronics and the (I assume) advantages of a stronger spark?

 

• Are there potentially better plugs (heat range, manufacturer, etc) to consider given my driving conditions?

 

Spark plugs with all their myriad of variations have been largely a mystery to me. Your wisdom and experience will be much appreciated!

 

 

I use the 306.  They work fine for me. I'm told they are a little bit hotter plug.  I'm just trying to remember what I was running before, but to be honest I didn't really notice any difference when I changed to the 306.  My trips are usually between one and two hours with speeds usually between 30 to 50 mph and sometimes up to 65 mph

[desoto1939]

Sparkplug Compairison Table.pdfSparkplug Compairison Table.pdfSparkplug Compairison Table.pdfThe Autolite 306 is a resiter type plug. The gapfor these plugs is 35 not the standard 25 with regular plugs.  I use the Autolite A9 plugs and have been for many years.  I gap these at 25.  Your car uses the 14mm with the 3/8 deep plugs.  Since you have not chnaged your plugs in over 10k miles and have not had any issue I would just try to get the same plugs again and use them.

 

If you have plugs that are working for you and the brand is available why change.

 

Here isa suggestion. Put the car in a dark garage without the overhead lights on. Open the hood start the car and let it idel to normal operating conditions with the choke off.

 

Look at the sparkplug wires to see if you are getting any blue lightning streaks coming off the wires. If you are then the wires are leaking current and they would also need to be replaced.

 

I know some owner do not like the Champion J11 but during my readings an investigating these are not the correct plugs for our MoPars.

 

 

Rich Hartung

desoto1939@aol.com

 

Blue Crown Spark Plug List PDF.pdf

Edited March 2, 2022 by desoto1939

[bamfordsgarage]

Well, that could have gone a lot better...

 

In hindsight,I would have been smart to saturate the spark plug wells with a good penetrant (I use 50/50 Acetone /ATF) for a few days before attempting removal. Even that may not have been enough — these suckers have been in place for years, and have surprisingly little metal connecting the base and ceramic.

 

Not going any further at this point... I can still move the car out of my sweetie's winter parking stall on five cylinders until I track down a new head gasket.  This well and the other five are now saturated with penetrant to make removal easier once I get the head off.

 

Live & learn ?

 

[Merle Coggins]

YIKES!! If you get them soaked down with some penetrating lubricant you may be able to use an extractor without needing to remove the head. Also, a bit of localized heat with an oxy/acetylene torch right into what's left of the spark plug may help break the rust bond. You may need to heat it and let it cool again to break the bond. 

[Bryan]

If you pack the hole with something to keep metal dust from going in it, you might be able to use a dremel to grind flat sides on the remaining metal to make a hex shape in a MM or SAE size of a socket wrench.  Hard to see.

[allbizz49]

PB blaster and heat. 

[Happy 46R]

Hi Chris, When I changed out my plugs I followed exactly what Desota1939 recommended. I went with what was working when I took out the old. Other than protecting the cylinder I am not sure what benefit removing the head will give you. If you can top dead center the piston, pack the space with a cloth and then wedge a ratchet extension into the remainder of the plug you may be able to get enough leverage to spin the remaining that may work or  maybe a tack weld to an old extension might work. Just a thought! good luck.  Dave

Edited March 4, 2022 by Happy 46R

[Sniper]

I always put a light coat of copper antisieze on my spark plug's threads.  50 years from now some DIY'er will be thanking me, lol.

 

One other thing I do is pull the plugs when the engine is warmed up and put them in when the engine is cold.  Got into that habit with my aluminum, aluminium to you Brits, headed engines so as to minimize the risk of stripping those aluminum threads.  Did it help?  Maybe not, but I have yet to strip them.

[bamfordsgarage]

Thanks all for your suggestions. Another helping of penetrant this evening.

 

Sniper, so where the heck were you when I installed these plugs a few years ago??

[Sniper]

9 hours ago, bamfordsgarage said:

Sniper, so where the heck were you when I installed these plugs a few years ago??

Learning the hard way what not to do, lol

[belvedere]

[Sam Buchanan]

4 hours ago, belvedere said:

 

The polite thing to do is provide a link.  ?

 

https://www.ebay.com/itm/384725715307?hash=item599370896b:g:tycAAOSw8hZiBF9x

 

https://www.homedepot.com/p/Husky-Pipe-Nipple-Extractor-Set-6-Piece-410-391-0111/309997715

Edited March 5, 2022 by Sam Buchanan

[bamfordsgarage]

Thank you Belvedere and Sam… those look pretty clever. Sadly the Home Depots here in western Canada apparently don’t carry them. 

[bamfordsgarage]

Success!

 

I clearly hit the panic button too early, fearing most of the remaining five plugs would be equally recalcitrant, and that succesfully extracting one or more stubs would prove very difficult (hence my need for a new head gasket).  

 

1. Two days soaking the five plugs and one stub with a 50/50 potion of acetone and ATF in the wells. 

 

2. Tried removing the other five plugs before going after the stub... if they were also going to break, not much point in working on the one stub first. The other five did come out but not without some serious twisting.

 

3. The broken #2 plug offered a clear path into the cylinder:

 

 

4. Two heat-cool cycles on the stub. One might have been enough, but I favoured overkill. I figured my first shot at removal would be my best chance:

 

 

5. So far, so good. In event that I was successful, I didn't want any debris falling into the cylinder. I made this loose-fit plug from the straight shank of a 7/16" bolt:

 

 

6. I shaved the end of a 3/8" extension nut to allow a tight fit into the stub,  and removed some plating to aid with brazing it into place:

 

 

7. Rat-a-tat-tat into the hole followed by a minute or so of medium blows to help dislodge the rust bond:

 

 

Continued next post...

[bamfordsgarage]

Continued...

 

8. Brazed the extension nut into the stub. This brazing alone was probably enough heat to break the rust bond without the earlier heat cycles:

 

 

9. Nut and stub turned out as easy as you hope for. Three or four foot pound at most:

 

 

10:  This is a mock-up, but how I'll be installing the replacement plugs (which are the exact same type that come out. Minus the rust):

 

 

Thanks to all for your suggestions and encouragement. Now where's my gapping gauge...

 

[RobertKB]

Glad all worked out well. New plugs will double the horsepower of the old heap!!?

[bamfordsgarage]

A quick follow-up to the previous posts re my search for a regular miss...

 

Compared the six existing spark plugs including the #2 stub:

 

 

All seemed OK aside from a rather crusty #6:

 

 

Based on this chart and others, #6 appeared to suffer from excess oil, oil additives, or fuel additives. I discounted the additives possibility, in that 1) I don't use any, and 2) only the one cylinder was affected:

 

 

Next step compression test, which was my plan on Wednesday afternoon before breaking off the #2 plug. Given the appearance of plug #6, my expectation was a ring problem in that cylinder:

 

 

To my surprise, if there's a ring problem it's apparently a relatively minor one in cylinder #3, but there are clearly valve issues in #2 and #6.

 

Installed the new plugs (gapped to 0.035 for resistor plugs), fired up the engine and the miss is still there. Strangely, it still sounds like only the one cylinder despite valve problems in two.

 

I have a couple other vehicles down for major repair, so the old heap is going to have to wait its turn. One good thing about the old car hobby... it keeps me off the street!