Spark plug porcelain breaking
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5th Wheeling
Joined: Dec 2006
Posts: 38
Likes: 3
Spark plug porcelain breaking
a 1973 Ford F350 with a 390. Just rebuilt the motor 400 miles ago. The previous motor and this motor both break the porcelain on the spark plugs. They don’t come loose out of the hole but will crack and break the porcelain on the plugs. What would be causing this? I’ve always run auto light, spark plugs and never have had this issue in any other vehicle
FTE Legend
Joined: Nov 2015
Posts: 30,886
Likes: 4,119
From: Angier, NC
It is the same plug(s) that are breaking?
Are you using a spark plug socket when installing them or a normal socket?
I have never seen them break on their own it is the socket that gets cocked and snaps it.
Dave ----
Are you using a spark plug socket when installing them or a normal socket?
I have never seen them break on their own it is the socket that gets cocked and snaps it.
Dave ----
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5th Wheeling
Joined: Dec 2006
Posts: 38
Likes: 3
five and six mostly but will be random sometimes. Using a spark plug socket.
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5th Wheeling
Joined: Dec 2006
Posts: 38
Likes: 3
it’s the porcelain on the boot side that breaks. They are spark plugs that the catalog says is for the motor. I torque them to spec.
Logistics Pro
Joined: Jun 2018
Posts: 3,551
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Same here. I would guess his spark plug socket is missing the rubber.
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5th Wheeling
Joined: Dec 2006
Posts: 38
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it’s not missing it’s rubber. They don’t break when I tighten them in. It’s after it’s ran a while and the porcelains will be broken.
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5th Wheeling
Joined: Dec 2006
Posts: 38
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not that I can tell. I have 180° thermostat in it and the temp gauge barely gets into the normal range. I don’t know the actual degrees that the engine is getting
Cargo Master
Joined: Jul 2005
Posts: 2,309
Likes: 364
From: Kansas
do you have an infrared thermometer? I would run it hard then check the temps around the plugs/exhaust ports on 5 and 6 and compare to other cylinders that have never broken. Do you notice any pinging/detonation under acceleration?
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5th Wheeling
Joined: Dec 2006
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autolites. Used them for years in everything I’ve owned this is the only engine I have a problem with them.
FTE Legend
Joined: Nov 2015
Posts: 30,886
Likes: 4,119
From: Angier, NC
Like the others have said been changing plugs since the 70's too and never see them break when installed in a motor.
I might give Champ or NGK's a try to see what happens with them.
When you pull the broken ones out what do the hole side look like? Running lean / rich / just right or ?
What type of plug wires you running do they have sleaves to keep the wire from melting on a manifold / header?
Running manifolds or headers?
Dave ----
I might give Champ or NGK's a try to see what happens with them.
When you pull the broken ones out what do the hole side look like? Running lean / rich / just right or ?
What type of plug wires you running do they have sleaves to keep the wire from melting on a manifold / header?
Running manifolds or headers?
Dave ----
Hotshot
Joined: Feb 2004
Posts: 10,785
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From: The Shenandoah Valley
I don't recall the issue he was dealing with, but my old Sgt. & buddy "Leon" had a '80s F-250 to pull his big horse trailer, it had a 460 in it, and what ever the problem was .... it was fixed with new plug wires with insulated ceramic boots as I vaguely recall. I likely knew once, ... but whatever .... it was heat related, but I took it to be to protect the wires?
Maybe was to protect plug bodies from exhaust manifold heat.
Maybe was to protect plug bodies from exhaust manifold heat.
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