#6 Spark Plug After Rebuild

[jtan540]

Long story short...rebuilt my 200ci .030 over block with new pistons, rings, bearings, and got a valve job done on the head. Start the thing and baby it comes to life. Check spark plugs to see how they are burning...all are burning to perfection except cylinder #6. Here is a picture of what the plug looks like:

Half the plug is fouled and half of it is fine(the resolution on the picture isnt amazing but its what i had on my camera phone). Anyways, I swapped plugs with a different cylinder and plug wires as well and still fouling. The only thing I can think of is that I have headers and I wrapped pipe #6 in header wrap due to its close proximity to the starter. I want to shield as much heat as possible from the starter cause swapping it out is a darn pain. Maybe the wrapped header is causing a rich mixture(?) Any other opinions/comments greatly appreciated.

 

[bubba22349]

Check spark plugs to see how they are burning...all are burning to perfection except cylinder #6. Half the plug is fouled and half of it is fine. Anyways, I swapped plugs with a different cylinder and plug wires as well and still fouling. The only thing I can think of is that I have headers and I wrapped pipe #6 in header wrap due to its close proximity to the starter. I want to shield as much heat as possible from the starter cause swapping it out is a darn pain. Maybe the wrapped header is causing a rich mixture(?) Any other opinions/comments greatly appreciated.

Doubt it on header wrapped making it rich, it’s after combustion! Is it missing? Things to check out: compression reading in 6 hole compared to others, intake valve stem seal or guides on #6. Vacuum leak. Check ohm resistance on the plug wire, for carbon tracking on cap. What heat range plugs?

 

[jtan540]

There is a slight and almost unnoticeable miss...Heat range is correct and head recently got a valve job so I doubt seals/guides would be an issue. But good point I will get down to compression/electrical testing and troubleshoot from there...

 

[ludwig]

Pull the plug #6 wire while it is running and see if there is a difference. If there is none, it's the ignition in that cylinder.

 

[aribert]

Is this oil film or exhaust soot?

After the 170 engine in my Falcon was rebuilt (back in about '75) #3 & #4 plugs would foul over exteded periods of time and had to be cleaned. As the miles piled on the fouling became more severe and I needed to clean the plugs every 500 to 1000 miles or I would get an engine miss. After about 125K miles of this, oil consumption (that started out at about 1500 miles/qt) was down to about 600 miles/qt. I'm guessing that a couple of the valve guides were out of spec on the rebuilt head. The compression was in line with the other cylinders. Not saying that this is your issue - just saying that it is possible if it is an oil film instead of exhaust soot.

 

[ponyrider200]

I had the head for my I-6 200 rebuilt professionally 2 years ago. Since then, I have had the exact same problem of the #6 piston. The spark plug show clean burn on one side, and oily on the other. It started there about 6 mos after the build, and has gradually spread to #5 and #4. I am very interested in what the forum thinks the problem is. Is this a bad exhaust valve? I did a compression check, with the following results:

#1 130, #2 125, #3 135, #4 120, #5 110, #6 95. I squirted a tablespoon of oil into each cylinder and retested, and compression improved abot 5 pounds.

 

[jtan540]

It is oil film...and it doesn't accumulate after several hundred miles of driving...try about 20.

Pulled the plug wire and there was a significant difference so I have ruled that out. I have yet to check compression but will post numbers once it stops raining down here in Southern California...yes, I did say that wretched 4 lettered word. RAIN.

BTW is there any way of ruling out the guides as the problem...without actually pulling the head off?

 

[bubba22349]

Is this a bad exhaust valve? I did a compression check, with the following results:

#1 130, #2 125, #3 135, #4 120, #5 110, #6 95. I squirted a tablespoon of oil into each cylinder and retested, and compression improved abot 5 pounds.

Yes it maybe a burnt Ex. valve, however if this is an early style head could also be an exhaust seat this is more likely (early heads didn’t have hard seats of late heads). Also could be a worn guide or guides. You test results do show you will need to pull the head for repairs. Sorry about that

 

[bubba22349]

It is oil film...and it doesn't accumulate after several hundred miles of driving...try about 20.

Pulled the plug wire and there was a significant difference so I have ruled that out. I have yet to check compression but will post numbers once it stops raining down here in Southern California...yes, I did say that wretched 4 lettered word. RAIN.

BTW is there any way of ruling out the guides as the problem...without actually pulling the head off?

As you said "oil after 20 miles" This really can only be a guide or seal!

Yeah it sure is raining here Socal today. If you have an air compressor maybe you would see it blowing air up the guide! If you can pull the valve spring on 6 and you can feel a bad guide. Set #6 to TDC and stuff some cotton clothes line rope tight into the cylinder or air if you have it (so valve dosn't drop out) I use a small spring compressor than to remove spring. Good Luck

 

[ponyrider200]

Thanks Bubba...that's what I was thinking too. Well winter is coming, and this will give me something to do.

 

[tony1963]

I have an 81 head on an 81 vehicle and had a similar problem prior to rebuild. It was coolant flashing against the spark plug.

Was your head checked for cracks?

 

[jtan540]

Wow...so lucky me, I took the valve cover off and looked at the head...intake valve didnt have a valve stem seal! None at all. The head was rebuilt by one of the best shops down here in San Diego but I suppose everyone is allowed one mistake :nono: , one that cost me 34 cents at Napa and 20 mins of my time 8)

 

[bubba22349]

:wow: glad was an easy fix