Could use some spark plug reading help

Discussion in 'Engine Topic' started by jvle95, May 20, 2021.

  1. jvle95

    jvle95 Veteran Member

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    I seem to be burning oil in my 355. It doesnt have a ton of miles on it but was built about 20 years ago with the heads being swapped out some years later. Typical street motor, 355, 9.8:1 comp, XE268, AFR 195 (pre eliminator heads), RPM Air Gap and Quickfuel 750VS.

    I do not see any smoke regularly but have noticed it a time or two during both hard acceleration and decceleration. Just starting to investigate. No big noticable oil leaks from the pan or valve covers or anywhere else. Pulled the plugs today and thought I would get some opinions on what you see. Numbers 1 & 2 seem to be much darker than the rest. Opinions?
    Thinking compression test and leak down test next.
    tempImageNc0e4W.png
     
  2. 73 Z

    73 Z Veteran Member Gold Member

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    Possibly the valve seals, the plugs don't look gas fouled.
    Not many miles in 20 yrs = dried up valve stem seals.
    If no notable performance has been lost a compression/leak down test is not necessary, but a good idea to see where its at.
     
  3. 1980RS

    1980RS Veteran Member

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    Looks like the typical Air Gap mixture distribution array. I put a 1" spacer on my BBC and it helps clean that up a bit. You may need to cross jet the carb to get it right or switch to a single plane intake manifold. Most likely if it's using oil look close at the pcv and valve guide seals.
     
  4. jvle95

    jvle95 Veteran Member

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    Forgot to mention, I did look at the PCV. No oil residue in the hose and running tall baffled valve covers. Dont have the PCV part number off hand, I will check to insure its correct. My thought is it is losing oil through valve seals and thought plugs would point that direction, but that doesnt seem to be the case. Performance seems to be what it has always been but its burning the oil pretty quick. Probably 1 1/2 qts in less than 500 miles.
     
  5. 73 Z

    73 Z Veteran Member Gold Member

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    1.5 less than 500 miles. Sounds like a bad piston oil rings, or oil/piston return holes are gunked up.
    Or a combo of, seals/rings/piston oil return holes.
     
  6. 1980RS

    1980RS Veteran Member

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    20 years ago I am betting the valve seals are hard as a rock. Do the prosses of elimination, plug the pcv and drive it for a while with the oil at the full level, if it does not use any then that's the problem. After that replace the valve guide seals and only one thing left, rings. Are you using synthetic oil in this engine?
     
  7. jvle95

    jvle95 Veteran Member

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    Not using synthetic. Currently using Valvoline VR1 10w/30. I will work through the process of elimination for sure. Wouldn't the plugs show more signs of oil if it was burning that much?
     
  8. Z28PILOT

    Z28PILOT Veteran Member Lifetime Gold Member

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    I d bet on oil seals at very least. My old never rebuilt 74 454 needs oil seals in the worst way .Puffs a small amount after it sits in the garage a week at start up , but doesn’t smoke after that and not hard on oil . I had to replace main seals and oil pan gasket , it use to leak like crazy and leave puddles smh . Have somebody watch your start up and follow you down the road once it is warmed up . Most likely you ll be ok with new seals, but for me 1.5 qt oil 500 miles is too much and may point to rings unless your blowing more oil out underneath while running than you suspect .
     
    Last edited: May 21, 2021
  9. COPO

    COPO Veteran Member Lifetime Gold Member

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    I would try 15w40 oil which has more detergent which will help keep the ring lands clean along with the oil rings/expander and drain back holes. Then go on a steady drive at 60 mph for 30 min and read the plugs, the plugs will reach self cleaning mode at a certain temp. Or you can go for 3 qtr mile blasts on an open road and read the plugs.

    I like the color of #6 plug.
    Are you using R45TS plugs? If your doing more city driving then a hotter plug such as the R45TS is better than a R43TS. If your using NGK plugs then their higher numbers mean a colder plug, it’s reverse compared to GM AC plugs.
    You shouldn’t have a colder thermostat than a 180*. 180* minimum or the engine is too cold.
     
    Last edited: May 21, 2021
  10. jvle95

    jvle95 Veteran Member

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    Currently running the Accel 416S plugs. This is my first run with these. Went to them because they are slightly shorter and my number three plug is very tight to the header tube. Kept burning plug boots. With teh 416S I gained just enough clearance to put a sleeve on the boot to keep it from burning.

    I probably mistitled this thread. My thinking is that I would have seen a plug or plugs that showed more signs of oil usage and after pulling them I do not really see that. I have run AC plugs in the past R44TS I think, maybe R45TS, with good results. The car is street driven for fun.
     

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