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 Stock Plug for reference, Probably too hot. 
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Joined: Sun Jun 23, 2013 1:41 pm
Posts: 375
Location: Phila. Penn.
Thought this might be interesting to at least a few. At least to me, I'm finding it interesting to see what 'normal' factory stuff looks like. It gives me some reference when looking at stuff from my hot rodded engines.
Champion RN14YC
From a stock .030 over rebuild of an AMC 360 Jeep engine.
Spark plug has 20 minutes or so of break in at 2000 rpm and about 100 miles of highway and local driving.
No wide open throttle (thankfully as I found the timing had been set 10 degrees advanced)
Checking the FSM and the owners manual the correct plug should be a Champion RN12YC.
Looks to me like erosion of the electrode. Surprises me that it would be noticible after so little run time.

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Mon Feb 06, 2017 1:06 am
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Joined: Fri Feb 08, 2013 2:37 pm
Posts: 1744
Does have a nasty look for only 200 miles, but looks like fuel or oil deposits. Any possibility the PCV valve is sucking oil from the valve cover or wherever it is? Is there a freshly oiled gauze (K&N type) filter. The edge of the center electrode looks OK, have you compared it (the sharpness of the edge) to a new one? It does look like it was a little warm, but if there is no WOT time that seems odd. You better use the cooler plug. With only 200 miles the plugs should appear almost unused.

Mon Feb 06, 2017 2:23 am

Joined: Sun Jun 23, 2013 1:41 pm
Posts: 375
Location: Phila. Penn.
Yes it is possible. I was rather surprised to see a little oil around the breather. That says to me there's blow by greater than the pull on the PCV. It's nothing like the old worn engine, but I'd expect it to be clean. When I pull the carb today I'll examine the PCV valve.

Air filter is a paper throw away type. Clean as whistle. PCV valve draws from the valley. The molded S hose that connects it was getting soft and the replacements which were available in 2015,have disappeared. I'll have to see how bad it is and if something needs to be cobbled together.

Mon Feb 06, 2017 9:48 am
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Joined: Sun Oct 23, 2016 5:52 pm
Posts: 138
Location: Canada
Surprising center electrode erosion, indeed.... cupped looking even. Definitely go with the colder plug...


1986 Mustang convertible. Originally 3.8L V6 with EEC-IV CFI.
Now has a Holley List-4412-2, and averages 34 (28 US) MPG.
If you're ever bored - some narrow band O2 tuning video of this thing:

Wed Feb 08, 2017 7:27 pm
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Joined: Fri Feb 08, 2013 5:50 pm
Posts: 2363
Are they all that way?

Thu Feb 09, 2017 10:57 am

Joined: Sun Jun 23, 2013 1:41 pm
Posts: 375
Location: Phila. Penn.
Mark, It's a bit of a pain due to the AIR tubes and such. I'll take all the spark plugs out when I get back down there in a few days after the salt clears off the roads.
I'll check compression as well. I waffled on doing that because somehow a bunch of the flexplate teeth got chewed up when the new engine was put in. I don't know how h*ll they did that.

I did find some more possible causes of problems as I was getting ready to put the carb back on.
There was some odd routing of wires and vacuum hoses and it looks like a manifold vacuum hose was broken. The one that supplies vacuum to the distributor advance. Also a delay valve and the wires to the distributor got hot enough to melt insulation. Not terrible, but that moved up my plan to remove the wire harness go over the whole thing for damaged insulations, bad connections, etc. Then put new convolute on it and route it all back where its supposed to be.

Thu Feb 09, 2017 11:12 pm
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Joined: Sun Jun 23, 2013 1:41 pm
Posts: 375
Location: Phila. Penn.
All the plugs look more or less similar. With a hand held lens I didn't see the electrode cupping that shows in some photos.
All have black about a thread of black on the shell and about 1/8" up the strap. One side of the insulator is fairly clean while the other side is mottled brown with speckles.
All of the plugs were installed very lightly - guessing around 10 ft lbs based on effort to remove.
Install spec for this engine is 25 ft lbs.

Compression is within spec although I'm not thrilled the spread. Test was done cold and the battery was assisted after #3 with my ancient battery charger. A recheck of #3 at the end didn't show any measurable variation due to slower starter speed. A check of #4 with 4 drops of 30wt oil showed no improvement in pressure.
I couldn't check compression check of cylinders 6 & 8 because the heater box is in the way of the compression checker's hose. I need to find or alter a spark fitting and an air hose with a 45 or 90 degree fitting. As I type this I remember I have a rubber nosed checker I could hold against the hole while using the remote starter switch.

All hit 95-100 psi in the first bump.
#1 & 3 hit 140 psi in 3 bumps.
# 5 hit 140 in 4 bumps
# 7 130 psi
#2 120 psi
#4 130 psi

AMC Jeep 360 cid v-8,
Factory Spec. 120-140 psi (min) 30 psi maximum variation allowable.
CR 8.25

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Thu Feb 16, 2017 12:26 pm
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It looks too rich. I have some plugs here out of a '72 318 Mopar with about 20,000 miles on them that don't have that much deposit.

Thu Feb 16, 2017 3:04 pm
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