Smog tube pipe inserts

Discussion in 'Original Drivetrain Topic' started by tms71z28, Apr 23, 2012.

  1. tms71z28

    tms71z28 Member

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    Apr 9, 2005
    CO
    Has anyone removed the original smog tube from the exhaust manifold from a 1970-71 Z28?

    Do you know the length of the pipe insert?

    The GM pipe insert is 3 1/8" long.

    Years ago I had an auto shop Install my original exhaust manifolds and the smog tubes. I supplied the GM pipes for the tubes. When I removed the smog tubes and the pipes recently they were less than 2” long. I’m not sure if the auto shop cut them down or something else changed the length.

    Any information would be greatly appreciated.
     
    Last edited: Apr 23, 2012
  2. mgoad1971

    mgoad1971 Veteran Member Lifetime Gold Member

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    Jul 29, 2011
    Houston, Texas
    Assuming this is a 1980-81 Camaro California car???
     
  3. twozs

    twozs Veteran Member

    7,993
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    Aug 5, 1999
    hopewell jct ny
    why , his name is tms 71Z28 and his profile seems to verify that .
     
  4. mgoad1971

    mgoad1971 Veteran Member Lifetime Gold Member

    2,473
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    Jul 29, 2011
    Houston, Texas
    I don't judge a book by its cover;) .
    Smog tubes are different for BBC than SBC. I was just reaching for more info.
     
  5. Bob R

    Bob R Moderator Staff Member

    4,219
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    Jan 6, 2000
    Flower Mound, Texas
    Ran into this problem years ago. The Smog Tube inserts (the ones that go into the exhaust manifold). The replacements from GM are slightly longer than the originals. Not sure of the exact length at the moment. However if you use the current replacements (assuming they are still available and have not checked) will rub up against the exhaust valve stem. So what you have to do is just grind them down a bit. I honestly cannot remember how much I had to take off since it was years ago. It wasn't a whole lot but you definitely do not want it rubbing up against the valve. Not good.
     
  6. COPO

    COPO Veteran Member Lifetime Gold Member

    15,164
    37
    Sep 15, 1999
    Toronto Maple Leafs
    I'll measure mine. When GM still had them before selling them all off to a US Co, I purchased one since they were $12. ea. I just cleaned them and reused mine.
    [​IMG]

    The new one was the same as my originals from my 70.
    [​IMG]
     
  7. 70COPO

    70COPO Moderator Lifetime Gold Member

    1,040
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    Dec 28, 2003
    Chillicothe Ohio
    I had to shave mine back a bit also. Perhaps the cast depth of the insert hole on the manifold could have some casting variation?
     
  8. Bob R

    Bob R Moderator Staff Member

    4,219
    1
    Jan 6, 2000
    Flower Mound, Texas
    I just measured an original from a 1973 Z28. It is 2.691 long. Anything longer than this will contact the exhaust valve stem.
     
  9. Smokin'Joe

    Smokin'Joe Veteran Member Lifetime Gold Member

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    Aug 14, 2008
    Texas
    Not sure if this will help or add confusion, but I took a pic and measured one that I got from Bill Hodell for a 1970 BBC. They are almost exactly 2-1/2" long.

    BBC smog inserts from Bill Hodell
    [​IMG]
     
  10. DCL70

    DCL70 Veteran Member

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    May 5, 2007
    Merrimack, NH
    The smog tube shown in the photo below is from a 1972 LH exhaust manifold cast # "3989041" dated "F 23 72" (June 23 1972).
    The tube measures 2.68" long with a diameter of 0.32".

    Dave
     
    Last edited: Jun 1, 2012

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