Spark Plug Reading
Thread Starter
Melting Slicks
Joined: Apr 2007
Posts: 3,189
Likes: 111
From: Tolland CT
Spark Plug Reading
I took all of the plugs out of my LS5 to do compression tests.
Noted a familiar pattern, wondering what to make of it if anything.
Most plugs have a blackened spot on one side of the insulator.
Some more pronounced than others. The plugs are fairly new, haven't driven the car more than 50 miles or there abouts.
I'm attaching three photos of the plug from cyl #8. The pattern suggests a directional issue. Doesn't show around the whole insulator.
Noted a familiar pattern, wondering what to make of it if anything.
Most plugs have a blackened spot on one side of the insulator.
Some more pronounced than others. The plugs are fairly new, haven't driven the car more than 50 miles or there abouts.
I'm attaching three photos of the plug from cyl #8. The pattern suggests a directional issue. Doesn't show around the whole insulator.
Le Mans Master
Joined: Dec 2006
Posts: 5,557
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From: Oquirrh Mountains
St. Jude Donor '09
reinstall the plug and then mark the top of the spark plug with a sharpie so it will be oriented when you remove it. Looks like an oil control issue. Once oriented, it will tell you if it's rings or guides/seals.
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You may have a valve seal problem. However, to me, it looks like it may be running a little too rich and you are probably short tripping it too much. I would get the car out on a good 50 mile highway run and then take a look at the plugs.
Thread Starter
Melting Slicks
Joined: Apr 2007
Posts: 3,189
Likes: 111
From: Tolland CT
Could be valve seals though the heads were worked on as part of the rebuild. This engine has had very few miles since rebuild, mainly short trips to the local shop for some work which I wasn't equiped to handle and a short ride here and there. I'm just getting to the point where this car is driveable after a frame off.
You're right about taking it for a long drive before checking plugs. I was checking compression, noted the coloring of the plugs while they were out. For now I regard it a an oddity, look at them again later, once I get everything settled, mixtures set and some run time.
Race Director
Joined: Sep 1999
Posts: 11,360
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From: Plano TX
It's normal. The BBC places the plug right below the intake valve so any oil that collects on top of the valve when the engine is off will dump right onto the plug.
A small amount of oil on top of the valve is normal due to the PCV system and also that some oil has to go down the valve stems to lubricate them.
If you drive the car a longer distance and then look at the plugs the spot will be much less noticeable as it slowly burns off.
A small amount of oil on top of the valve is normal due to the PCV system and also that some oil has to go down the valve stems to lubricate them.
If you drive the car a longer distance and then look at the plugs the spot will be much less noticeable as it slowly burns off.
