Fouled #8 plug diagnosis
Thread Starter
Pro
Joined: Sep 2002
Posts: 541
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From: Epping NH
Fouled #8 plug diagnosis
I recently managed to replace all 8 plugs and ignition wires on my 69 L-46, with full ignition shielding. I am convinced that most of these cars never had plugs and wires 1, 2, 3 and 4 replaced during tune ups after that experience! Anyway, now that they are all out and have been replaced, I am wondering what can be told about the engine from the condition of the plugs. Most were a dirty gray, I believe due to leaded racing fuel that I have added to the original 11:1 compression engine. You can see this at exhaust too. Plug 8 however, was completely fouled with sticky oil. I do have an oil leak somewhere on the left rear that has managed to soak the starter. I will be replacing the valve cover gaskets with a set of Fel-Pro rubber and steel gaskets this week and hope to solve the leaky oil problem, but how would a leak explain the fouled plug?
Mark
Mark
Safety Car
Joined: Nov 2008
Posts: 3,726
Likes: 558
From: Seattle Washington
Sounds like You have a Oil control problem in the one Cylinder. Best Case is that You have a PCV Valve issue and the Oil is getting sucked in and its running down that Port into that Cylinder. Probably not. Or that Plug Wire or That Plug is dead. Next best is that the Oil Seal on that Cylinder Valves are shot and the Oil is getting in. Worst case is the Rings are shot on that Piston and need to be replaced.
I'd start out with the easy stuff. Does the PCV Valve run into the Intake anywhere near the Port leading to that Cylinder ? If You run the Engine with the old Spark Plug and wire does it sound different if You pull the Plug wire off ? If You pull the Valve cover off You might even see a missing Valve seal or find parts of it. A Borescope looking in the Plug hole will show the top of the Piston. If the Piston is clean with little or no Carbon out near the Cylinder its from Oil leaking by and not letting the Carbon stick.
I'd start out with the easy stuff. Does the PCV Valve run into the Intake anywhere near the Port leading to that Cylinder ? If You run the Engine with the old Spark Plug and wire does it sound different if You pull the Plug wire off ? If You pull the Valve cover off You might even see a missing Valve seal or find parts of it. A Borescope looking in the Plug hole will show the top of the Piston. If the Piston is clean with little or no Carbon out near the Cylinder its from Oil leaking by and not letting the Carbon stick.
Thread Starter
Pro
Joined: Sep 2002
Posts: 541
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From: Epping NH
At this point, I have replaced the plugs and wires. In the process of accessing 1 and 3, I disconnected the exhaust pipe from exhaust manifold, and the ceramic seal cracked and broke, so I am waiting for the new seal before firing up engine.
Engine was rebuilt < 20,000 miles ago, so I am going to cross my fingers on rings/piston.
i am replacing the valve cover gaskets this week (Fel-Pro performance rubber with steel inserts) and will be able to look into the heads. If valve seal is missing or broken, does the head have to come off for replacement? What am I looking for, pieces of rubber in the head?
Engine was rebuilt < 20,000 miles ago, so I am going to cross my fingers on rings/piston.
i am replacing the valve cover gaskets this week (Fel-Pro performance rubber with steel inserts) and will be able to look into the heads. If valve seal is missing or broken, does the head have to come off for replacement? What am I looking for, pieces of rubber in the head?
Drifting
Joined: Sep 1999
Posts: 1,970
Likes: 91
My 70 L46 would foul 43's in no time. In fact , r44 is what is called for and they weren't great either. Went with 45's and no issues.
As far as the bad 8 plug, I had that as well . Turned out the shield under the intake was keeping the intake from sealing at the 8 runner. Oil drains back that way. If you've had the block decked,, the head to intake alignment could be off and cause a oil leak among other issues.
Should mention I had the heads worked slightly to breath better to counter any percolating/hot start from running the hotter plug.
As far as the bad 8 plug, I had that as well . Turned out the shield under the intake was keeping the intake from sealing at the 8 runner. Oil drains back that way. If you've had the block decked,, the head to intake alignment could be off and cause a oil leak among other issues.
Should mention I had the heads worked slightly to breath better to counter any percolating/hot start from running the hotter plug.
Last edited by dennis; Jun 11, 2020 at 08:59 AM.
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Michael S. Palmer
Le Mans Master
Joined: Aug 2017
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From: Cool Northern Michigan
You are looking for either a black "O" ring, a black umbrella type rubber chunk or even a blue silicone type of broken seal. Once the broken seal leaves the valve-spring area, it usually travels towards the drain hole at the rear of the head.
You can change valvestem seals easily ON The Head if you have a Valve Spring Compressor Tool. You can get a cheapie for doing one or two valves springs, for around $10. Simple leverage type handle that attaches to the rocker stud / nut. Have a magnet ready for the split-locks.
For doing several springs you will want a better "cam-over" style compressor that allows you to remove springs with one hand, for around $50.
No need to buy a sparkplug air hose for repair on one cylinder. Just shove some soft, flexible rope in the sparkplug hole while raising the piston to TDC.
You can change valvestem seals easily ON The Head if you have a Valve Spring Compressor Tool. You can get a cheapie for doing one or two valves springs, for around $10. Simple leverage type handle that attaches to the rocker stud / nut. Have a magnet ready for the split-locks.
For doing several springs you will want a better "cam-over" style compressor that allows you to remove springs with one hand, for around $50.
No need to buy a sparkplug air hose for repair on one cylinder. Just shove some soft, flexible rope in the sparkplug hole while raising the piston to TDC.
Last edited by HeadsU.P.; Jun 11, 2020 at 09:49 AM.
Racer
Joined: Feb 2011
Posts: 252
Likes: 12
From: Fredericksburg Va.
I'm assuming it is running ok because you didn't mention it's running bad. Have you noticed smoke ? At start up...…..extended idle...…….or maybe coming down from high RPM to a traffic light...…..Pretty hard to hurt the lower end of these small blocks but certainly possible. I would start by installing a set of valve seals in it just because they are easy to do first. Then if that doesn't do it put intake gaskets on it....Bet intake gaskets take care of your problem.