A Spark Plug Conundrum
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A Spark Plug Conundrum
Several weeks ago I found that my #4 plug had virtually no gap. The gap was less then my thinnest feeler gage ( < 0.005 in). I swapped in a correctly gap plugged. Since then I've driven the jeep about 300 miles. Today I went to fill up the tank and when I started the jeep at the gas station it sounded like it was misfiring. After letting it cool down I inspected the spark plugs and the #4 plug again had virtually no gap.
I looked through the spark plug hole at the valve and didn't see any indication that the spark plug electrode had struck the valve. All four cylinders have the same Autolite spark plugs that I've used for years. My shop vac which sealed well around the spark plug hole did not appear to suck anything out.
Any idea what might be closing the gap on the plug or do I need to look forward to pulling the head?
I looked through the spark plug hole at the valve and didn't see any indication that the spark plug electrode had struck the valve. All four cylinders have the same Autolite spark plugs that I've used for years. My shop vac which sealed well around the spark plug hole did not appear to suck anything out.
Any idea what might be closing the gap on the plug or do I need to look forward to pulling the head?
Seth
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1942 MBT 10968 viewtopic.php?f=18&t=149552" onclick="window.open(this.href);return false;
1942 MBT 15799, USA 0217497
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Collecting Willys Engine Info. Please send me Engine #, Casting Date & Machining Date if known
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1944 MB 349858, 20620361
1942 MBT 10968 viewtopic.php?f=18&t=149552" onclick="window.open(this.href);return false;
1942 MBT 15799, USA 0217497
MVPA # 8587
Collecting Willys Engine Info. Please send me Engine #, Casting Date & Machining Date if known
- Bill H.
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Re: A Spark Plug Conundrum
Seth, IIRC the spark plug is not positioned above the valve but is above the piston. With a dial indicator or depth gauge check piston height on each cylinder. The top of the piston may be striking the electrode ever so slightly.
Bill H.
Welfare, a modern day career choice.
1962 AMC M422A1
1965 Stevens M416B1
2 Timothy 3:1-5
Welfare, a modern day career choice.
1962 AMC M422A1
1965 Stevens M416B1
2 Timothy 3:1-5
- Bill H.
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Re: A Spark Plug Conundrum
As a temporary test you can add one gasket washer to the plug and give it a go also. This won't fix the issue but it will tell you if the piston is smacking the electrode though.
Do you have any knocking or tapping?
Do you have any knocking or tapping?
Bill H.
Welfare, a modern day career choice.
1962 AMC M422A1
1965 Stevens M416B1
2 Timothy 3:1-5
Welfare, a modern day career choice.
1962 AMC M422A1
1965 Stevens M416B1
2 Timothy 3:1-5
- '42 Peep's Motorpool
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Re: A Spark Plug Conundrum
Hi Bill,
That is true of many engines, but not our beloved L134. IIRC its more or less over part of the valves. If it was over the cylinder it would make finding TDC much easier, sadly it isn't. At this stage I would suspect a valve has to be part of the equation, so it might be worth checking the valve springs and clearance on #4.
"Peep" was the name used by the Armored Force for the 1/4 Ton truck early in WWII.
'42 Peep's Motorpool
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Re: A Spark Plug Conundrum
I wouldn't pull the head until you can tell if there is a reason to do so. Not an expert at all, but from what I know of these engines I would start by checking that the valve clearance is correct, that the valve springs are ok and not broken, and then check to see if there is any indication of a bent valve (a leak down and vacuum test to test if it's seating fully, or abnormal noises or operation). Valves can rotate, so you may not necessarily be able to see (through the sparkplug hole) a specific point where it might have made contact with the plug if it rotated away from the hole, plus carbon might obscure evidence unless it was a pretty severe 'contact'!
What make and model sparkplug are you running? Any other symptoms you have noticed?
What make and model sparkplug are you running? Any other symptoms you have noticed?
"Peep" was the name used by the Armored Force for the 1/4 Ton truck early in WWII.
'42 Peep's Motorpool
'42 Peep's Motorpool
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Re: A Spark Plug Conundrum
I’ll check for a broken valve spring. I didn’t hear anything unusual from the engine when the exhaust note changed. I’m running Motorcraft A7C’s (not the Autolite 295’s that I thought were in the Jeep).
Edit: 0822 CST
I just looked and #4 plug was missing it’s gasket. I swapped it for an Autolite 295 with a gasket.
Edit: 0822 CST
I just looked and #4 plug was missing it’s gasket. I swapped it for an Autolite 295 with a gasket.
Seth
******
1944 MB 349858, 20620361
1942 MBT 10968 viewtopic.php?f=18&t=149552" onclick="window.open(this.href);return false;
1942 MBT 15799, USA 0217497
MVPA # 8587
Collecting Willys Engine Info. Please send me Engine #, Casting Date & Machining Date if known
******
1944 MB 349858, 20620361
1942 MBT 10968 viewtopic.php?f=18&t=149552" onclick="window.open(this.href);return false;
1942 MBT 15799, USA 0217497
MVPA # 8587
Collecting Willys Engine Info. Please send me Engine #, Casting Date & Machining Date if known
- Bill H.
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Re: A Spark Plug Conundrum
I'll wager to guess that does it.sjalbert wrote: ↑Mon Nov 11, 2019 6:03 amI’ll check for a broken valve spring. I didn’t hear anything unusual from the engine when the exhaust note changed. I’m running Motorcraft A7C’s (not the Autolite 295’s that I thought were in the Jeep).
Edit: 0822 CST
I just looked and #4 plug was missing it’s gasket. I swapped it for an Autolite 295 with a gasket.
Bill H.
Welfare, a modern day career choice.
1962 AMC M422A1
1965 Stevens M416B1
2 Timothy 3:1-5
Welfare, a modern day career choice.
1962 AMC M422A1
1965 Stevens M416B1
2 Timothy 3:1-5
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Re: A Spark Plug Conundrum
That seems to have worked. I’m surprised that the clearance was that tight.
Seth
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1944 MB 349858, 20620361
1942 MBT 10968 viewtopic.php?f=18&t=149552" onclick="window.open(this.href);return false;
1942 MBT 15799, USA 0217497
MVPA # 8587
Collecting Willys Engine Info. Please send me Engine #, Casting Date & Machining Date if known
******
1944 MB 349858, 20620361
1942 MBT 10968 viewtopic.php?f=18&t=149552" onclick="window.open(this.href);return false;
1942 MBT 15799, USA 0217497
MVPA # 8587
Collecting Willys Engine Info. Please send me Engine #, Casting Date & Machining Date if known
- '42 Peep's Motorpool
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Re: A Spark Plug Conundrum
Hopefully that was the cause! Might be a good idea to double check your valve clearance too, to be on the safe side.
To have two of those missing is odd,but assuming the old one didn't stick to the head (can happen if a seeping head stud allows coolant to pool into the well), it's a good reason to inspect parts before putting them on. Always good practice to inspect parts before installation anyway, but anymore you almost have to inspect them when you buy them. Case in point, I needed a universal joint on short notice (I needed it that day) and could not order from Ron (weekend), so I went to a local big-box parts store where they sold me a very cheap made in China universal joint that had a beat up box. Upon getting home and opening it I found that aside from the low quality, it was actually missing roller bearings. Looked like someone in the store had opened it up to look at it, or even that it was a return. That experience with shoddy parts and service further reinforced my pledge to buy from Ron Fitzpatrick over any other no matter how badly I needed it, I'd rather wait for Ron's to come (quick anyway) than waste money on junk or damaged parts.
To have two of those missing is odd,but assuming the old one didn't stick to the head (can happen if a seeping head stud allows coolant to pool into the well), it's a good reason to inspect parts before putting them on. Always good practice to inspect parts before installation anyway, but anymore you almost have to inspect them when you buy them. Case in point, I needed a universal joint on short notice (I needed it that day) and could not order from Ron (weekend), so I went to a local big-box parts store where they sold me a very cheap made in China universal joint that had a beat up box. Upon getting home and opening it I found that aside from the low quality, it was actually missing roller bearings. Looked like someone in the store had opened it up to look at it, or even that it was a return. That experience with shoddy parts and service further reinforced my pledge to buy from Ron Fitzpatrick over any other no matter how badly I needed it, I'd rather wait for Ron's to come (quick anyway) than waste money on junk or damaged parts.
"Peep" was the name used by the Armored Force for the 1/4 Ton truck early in WWII.
'42 Peep's Motorpool
'42 Peep's Motorpool
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Re: A Spark Plug Conundrum
It's a possibility the head has been resurfaced one time too many.
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Re: A Spark Plug Conundrum
NOS 6.48:1 Heads mike 2.140" (2-9/64").
2011 MVPA PIONEER AWARD - MVPA #1064
HONOR GRAD-WHEELED VEHICLE MECHANIC SCHOOL 1960 - US ARMY ORDNANCE SCHOOL(MACHINIST) ABERDEEN PG 1962 - O-1 BIRD DOG CREWCHIEF - 300,000+TROUBLE FREE M-38A1 MILES
LIFE MEMBER AM LEGION-40/8-DAV
7 MIL SPEC MAINTAINED MV'S
COL. BRUNO BROOKS (ARMY MOTORS) IS MY HERO
HONOR GRAD-WHEELED VEHICLE MECHANIC SCHOOL 1960 - US ARMY ORDNANCE SCHOOL(MACHINIST) ABERDEEN PG 1962 - O-1 BIRD DOG CREWCHIEF - 300,000+TROUBLE FREE M-38A1 MILES
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Re: A Spark Plug Conundrum
I've never had the head off and I've been running this engine for the better part of the last eight years.
Middle Plug (Motorcraft A7C) has been in the engine since 2015 and is the one I realized was missing the crush washer.
Left Plug (Champion RJ14) is the one I installed and closed up in about 300 miles
Right Plug (Autolite 295) is what's in now (and had previously been in the engine for about 20 years)
The A7C & RJ14 clearly protrude further into the engine.
Middle Plug (Motorcraft A7C) has been in the engine since 2015 and is the one I realized was missing the crush washer.
Left Plug (Champion RJ14) is the one I installed and closed up in about 300 miles
Right Plug (Autolite 295) is what's in now (and had previously been in the engine for about 20 years)
The A7C & RJ14 clearly protrude further into the engine.
Seth
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1944 MB 349858, 20620361
1942 MBT 10968 viewtopic.php?f=18&t=149552" onclick="window.open(this.href);return false;
1942 MBT 15799, USA 0217497
MVPA # 8587
Collecting Willys Engine Info. Please send me Engine #, Casting Date & Machining Date if known
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1944 MB 349858, 20620361
1942 MBT 10968 viewtopic.php?f=18&t=149552" onclick="window.open(this.href);return false;
1942 MBT 15799, USA 0217497
MVPA # 8587
Collecting Willys Engine Info. Please send me Engine #, Casting Date & Machining Date if known
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Re: A Spark Plug Conundrum
I run AC-45 plugs. I know these work fine.
Dino Falabrino
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On the "G" since 1998.
1943 GPW 102310 DOD 3-3-43
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Re: A Spark Plug Conundrum
I do too. As far as I am concerned they are a perfect match.
Another consideration, perhaps a piece of carbon broke loose and got mushed.
Another consideration, perhaps a piece of carbon broke loose and got mushed.
2011 MVPA PIONEER AWARD - MVPA #1064
HONOR GRAD-WHEELED VEHICLE MECHANIC SCHOOL 1960 - US ARMY ORDNANCE SCHOOL(MACHINIST) ABERDEEN PG 1962 - O-1 BIRD DOG CREWCHIEF - 300,000+TROUBLE FREE M-38A1 MILES
LIFE MEMBER AM LEGION-40/8-DAV
7 MIL SPEC MAINTAINED MV'S
COL. BRUNO BROOKS (ARMY MOTORS) IS MY HERO
HONOR GRAD-WHEELED VEHICLE MECHANIC SCHOOL 1960 - US ARMY ORDNANCE SCHOOL(MACHINIST) ABERDEEN PG 1962 - O-1 BIRD DOG CREWCHIEF - 300,000+TROUBLE FREE M-38A1 MILES
LIFE MEMBER AM LEGION-40/8-DAV
7 MIL SPEC MAINTAINED MV'S
COL. BRUNO BROOKS (ARMY MOTORS) IS MY HERO
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Re: A Spark Plug Conundrum
That might have been the caae with the A7C (which is essentially the same plug as the AC45) because I ran it for several years without a problem. I'm not sure how the RJ14 ended up in my road spares box, but it's clearly substantially longer. With the crush washer the A7C & the 295 are the same length.
Seth
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1944 MB 349858, 20620361
1942 MBT 10968 viewtopic.php?f=18&t=149552" onclick="window.open(this.href);return false;
1942 MBT 15799, USA 0217497
MVPA # 8587
Collecting Willys Engine Info. Please send me Engine #, Casting Date & Machining Date if known
******
1944 MB 349858, 20620361
1942 MBT 10968 viewtopic.php?f=18&t=149552" onclick="window.open(this.href);return false;
1942 MBT 15799, USA 0217497
MVPA # 8587
Collecting Willys Engine Info. Please send me Engine #, Casting Date & Machining Date if known
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