401 Started Smoking

Discussion in ''Da Nailhead' started by Kqqlcat, Jun 22, 2017.

  1. Kqqlcat

    Kqqlcat Well-Known Member

    Took the cat to get gas and it started to smoke out right bank. Plug closest to firewal is oil soaked. Engine has a little less than 8,000 miles on it since 1998. Does anyone have Ideas on what could have happened? What to look for?
  2. TrunkMonkey

    TrunkMonkey Well-Known Member

    Do compression test. Likely a ring issue. You might have broken a ring, or rings may be stuck.

    If stuck, you might get lucky with something like Marval Mystery Oil and soaking the cylinders, but realize that some things may provide a wide range of results.

    Also drain and inspect oil, and cut the filter and look for metal.

    But until you know more, I would not run it.

    322bnh likes this.
  3. SpecialWagon65

    SpecialWagon65 Ted Nagel

    I wonder if the oil passage in back could be leaking through the gasket- I know of that occurring out the back of the engine
    between head and block.
  4. telriv

    telriv Well-Known Member

    But the spark plug would NOT be oil soaked.
  5. Briz

    Briz Platinum Level Contributor

    had an Impala back in the day. Took her to the exhaust shop for new pipes and when I left the parking lot it started to smoke really bad. Found 1 oil soaked plug on #7. Pulled the head and pooped that piston out to find it had broken from the ring lands to the skirt.
  6. 1972Mach1

    1972Mach1 Just some M.M.O.G. guy.....

    How long since it last ran before taking it out today?
  7. ttotired

    ttotired Well-Known Member

    Sorry to say mate, but I see an engine build thread coming
    Do a compression test and oil test as above.
    My 364 was stuck when I bought the car, after 2 weeks of gentle coaxing, it freed up, and I got it started.
    It ran pretty good, but was smokey (single exhaust) and had a knock at idle that seemed to go away when it revved.
    Number 1 piston had lost its skirt.
    Funny thing was the compression was fine as the top and rings ect were still there, but I guess the top was rocking, allowing the oil into the cylinder.
    I have read that nailheads and broken pistons is not that much of a rarity
    You said the engine is 8000 miles old, was that with new pistons?

    I hope I am wrong
    I have to get an engine kit for mine yet, I will be restoring the rest of it before I do the engine
  8. kcombs

    kcombs Well-Known Member

    I had a Chevy with a 235 six in it that smoked really bad but had good compression. I was stopped by the Petaluma, CA police for excessive smoke in the late 1960's, he made me turn it off as he wrote the fix it ticket,something about the smoke bothering him. I didn't know you could get a ticket in those days for smoking exhaust. When I took it apart the oil rings were stuck in their lands and the compression rings were doing their job.
  9. 66electrafied

    66electrafied Just tossing in my nickel's worth

    The one closest to the firewall...yeah, that would be about right. Have you been running old or bad gas? When mine started smoking it was a combination of heat, old age and bad fuel; - the back wall of the piston down to the 1st compression ring blew out. Nice hole in the piston; smoked like a battleship at flank speed after that.
    Let's hope you're lucky and it's either a rusted out gasket or a broken ring.

    Put it on a vacuum gauge; - the number will be low, (probably 10) and the needle will bounce like crazy between 8 and 16. If this is the case, you've got a broken ring or a bad head gasket.
    Aussie V8 likes this.
  10. John Codman

    John Codman Platinum Level Contributor

    You said the engine has 8,000 miles on it since 1998. You did not say that the engine had been rebuilt then. What is the total mileage? As was asked earlier - did it get new pistons when it was "rebuilt"? It would be very unusual for a decent Nailhead piston to self-destruct at only 8,000 miles. It would not be at all surprising for one to do so at about 100,000 miles.
  11. 322bnh

    322bnh Well-Known Member

    If it runs smooth with no abnormal noises after cleaning or changing the plug drive it until fully warmed up and see if it clears.
    Could be oil getting in through the valve guide at the rear: some rebuilt replacement rocker assemblies put out a huge shower of oil making it necessary to install valve guide seals; the replacement pushrods are much thicker than stock and inhibit oil return if using a very thick oil.
  12. JZRIV

    JZRIV Platinum Level Contributor

    Gee Briz - pooping that piston out had to be painful ;)
    Briz likes this.
  13. Briz

    Briz Platinum Level Contributor

    Grin and bare it.
    436'd Skylark likes this.
  14. Kqqlcat

    Kqqlcat Well-Known Member

    Sorry for asking questions and not answering posts but was at Back to the 50's all weekend. So engine was completely rebuilt aout 8,000 miles ago, had car out 4-5 times this year with no problems, it runs very good not rough at all, very light blue smoke not heavy at all. I'm thinking valve guide or valve seal. Will do compression check on all cylinders, if good will do a visual on valve seals if it has them. How do I check to see if they put in bronze guides. Oh I forgot I remeber seeing one larger pushrod when I had the valley cover off but I don't remember which one it was. You might have something there.
    Thanks for the reponses.
    Last edited: Jun 26, 2017
  15. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    If for some reason, the oil drain back holes in the head are blocked, oil will sit up in the rear of the head, and be sucked down the guides during periods of high vacuum. Had this happen to me when I replaced valve cover gaskets, and didn't clean the old gasket pieces out. They blocked the drain back. Car smoked at idle. This was in my very early inexperienced days.:(
  16. wkillgs

    wkillgs Gold Level Contributor

    A blocked return sounds more likely, but also check the pcv system. There should be a splash shield on the rocker shaft to keep oil away from the pcv valve.
  17. telriv

    telriv Well-Known Member

    If it DID have bronze guides installed almost guaranteed one came loose. Because of the side loading of the guide when the valve is opened is even MORE prone to happening especially with a non stock higher lift cam.
  18. Kqqlcat

    Kqqlcat Well-Known Member

    Okay I did a compression check and all are 180 but the wet plug one was 170. I don't know if a bad guide or seal could do that. Could it be a head gasket?
  19. 8ad-f85

    8ad-f85 Well-Known Member

    Why guess? Chuck some air into the cylinder at TDC to rule out rings and valve seats after you take the VC off and look in there.
  20. 1972Mach1

    1972Mach1 Just some M.M.O.G. guy.....

    I agree. Pull the valve cover and give it a look see first, then put some air to it. You'll know for sure where the issue is by where the air is escaping to. I've seen engines compression test fine, but have 40% leakdown. Your 170-180 difference isn't enough to worry about, if everything else checks out ok, by the way......

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