273 cylinder out

Small Block Mopar Engine

  1. Mouse action

    Mouse action Well-Known Member

    Messages:
    219
    Likes Received:
    388
    Joined:
    Oct 16, 2019
    Location:
    Brooklyn
    Local Time:
    3:57 PM
    A little help from the Mopar Gods ?
    My 273 seems a little low on power ,so a cylinder is kinda dead,if I pull of the plug wire the is no difference in running however the plug is firing.a compression test showed the cylinder to be a bit low but nothing to be concerned with,no oil smoke,I took the valve cover off and all is operational under there.
    Now I do not know any history on the car ,but was told buy the dealer who sold it to me it has 318 heads on it,,,,,any of this sound right ? what am I missing to do ?
     
    Last edited: Jan 17, 2020
  2. 66fs

    66fs FABO Gold Member FABO Gold Member

    Messages:
    4,833
    Likes Received:
    1522
    Joined:
    Sep 9, 2009
    Location:
    Greenwood, South Carolina
    Local Time:
    3:57 PM
    If you have compression close to the others, what are the readings?, it should make a difference. Check to make sure you have good cap, rotor, wires, plug, ignition box. I had an MSD 5C box and the ignition was less than par, put my 20 year old chrome box back on, problem solved. While you are at it, check TDC they can be way off.
     
    • Agree Agree x 1
    • Mattax

      Mattax Just the facts, ma'am FABO Gold Member

      Messages:
      10,808
      Likes Received:
      6770
      Joined:
      Feb 7, 2013
      Location:
      Phila. Pa
      Local Time:
      3:57 PM
      remove the valve covers.
      a. See what type of rockers it has.
      b. There will be several casting numbers. Write them down and/or take photos.

      These will be your first clues as to whether the heads have been changed and whether it may have mechanical or hydraulic lifters.

      If its mechanical lifters, the lash may need adjustment.

      How did you check for spark at the plug? with an in-line tester ?
       
      • Agree Agree x 2
      • toolmanmike

        toolmanmike FABO MODERATOR Staff Member FABO Gold Member

        Messages:
        50,687
        Likes Received:
        35750
        Joined:
        Jan 18, 2006
        Location:
        Iowa
        Local Time:
        2:57 PM
        Like mentioned, a compression test is your first diagnosis. There is a dozen different things that could cause a dead cylinder but first things first.
         
        Last edited: Jan 16, 2020
        • Agree Agree x 2
        • AJ/FormS

          AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

          Messages:
          18,596
          Likes Received:
          6707
          Joined:
          Jan 19, 2014
          Location:
          South-Central Manitoba,Canada, 900ftelevation
          Local Time:
          2:57 PM
          Is it no 5 or 7
          These fire one after the other, and if you cross them, you will have Two dead cylinders.
          But if they are not crossed, then, if the wires are running side by side, then either can still fire the other by induction, especially with the plug out of the cylinder, and the case grounded. This can happen between any two cylinders that have the wires running parallel and close together.

          However, just to be sure, make note of the troublesome cylinder, and swap it's plug for another one. If the trouble follows the plug, throw it away. I have seen many instances of a cracked porcelain leaking the spark away in the cylinder under compression, yet fire fine in atmosphere. If you find out that this is your problem, then you still have to figure out why this happened.

          Often you can recognize the crack by the carbon track...... but not always.
           
          Last edited: Jan 16, 2020
        • Wyrmrider

          Wyrmrider FABO Gold Member FABO Gold Member

          Messages:
          3,499
          Likes Received:
          1677
          Joined:
          Sep 5, 2016
          Location:
          los angeles
          Local Time:
          12:57 PM
          plug wires carbon cor can burn on the inside and arc inside the insulation till the gap gets too big
           
        • Mouse action

          Mouse action Well-Known Member

          Messages:
          219
          Likes Received:
          388
          Joined:
          Oct 16, 2019
          Location:
          Brooklyn
          Local Time:
          3:57 PM
          Thanks for all the support,I’ll start back on it ASAP.
           
        • krazykuda

          krazykuda Well-Known Member FABO Gold Member How-To Section Editor

          Messages:
          53,806
          Likes Received:
          18816
          Joined:
          Aug 20, 2007
          Location:
          Orland Park, IL
          Local Time:
          2:57 PM
          273 and 318 heads are completely interchangeable... Copy down the casting number on the head if you still have the valve cover off....

          What cylinder is giving you the problem???

          Try running it in the dark and see if any spark plug wires are arcing....


          And you can always trust what a dealer tells you.... :bs_flag: Not!!!
           
        • 66fs

          66fs FABO Gold Member FABO Gold Member

          Messages:
          4,833
          Likes Received:
          1522
          Joined:
          Sep 9, 2009
          Location:
          Greenwood, South Carolina
          Local Time:
          3:57 PM
          Looking at the car, 64 or 65 Barracuda, 318 heads would not be interchangeable because the 64-65 intake bolt angle, and 318 heads would be a power loss in flow and compression.
           
        • nm9stheham

          nm9stheham Well-Known Member

          Messages:
          12,090
          Likes Received:
          3934
          Joined:
          Dec 20, 2013
          Location:
          Waynesboro, VA
          Local Time:
          3:57 PM
          The late 273's had the same heads as 318's; the last 3 digits on those head casting numbers are 675. What year is your car/engine? (Of course, heads/engine could have been swapped out regardless of year.)

          So how low is the 'low' compression on that cylinder? The rings can be very poorand if the rings are shot, oil will get up on the top ring and make it seal better at the low piston speed when cranking. And, the ring grooves can be shot and the ring will flutter more at RPM and not seal much at all.

          As in post #3, if there is a valve clatter in that cylinder, then a valve adjustment may do wonders.

          Also, get a vacuum gauge and hook it up to a port under the carb to read manifold vacuum at idle. See what the idle vacuum rads, and if there is any steady fluttering/pulsing of the vacuum gauge needle.

          And, get a voltmeter, put it on ohms range, and measure end-to-end resistance of each spark wire. Standard resistance wires will typically be in the 3,000 to 7,000 ohm range and should not be any higher than 10,000 ohms.

          BTW, a spark jumping the small gap of a spark plug in open air is totally meaningless. It takes only 2-3,000 volts to jump that gap in air, but will take up near 20,000 volts to jump the same small gap in a compressed fule-air mixture. A good spark can easily jump a 1/4" gap in open air.
           
          Last edited: Jan 18, 2020
          • Like Like x 1
          • 66fs

            66fs FABO Gold Member FABO Gold Member

            Messages:
            4,833
            Likes Received:
            1522
            Joined:
            Sep 9, 2009
            Location:
            Greenwood, South Carolina
            Local Time:
            3:57 PM
            Casting number of 68-69 273's and 318's is 675 with open chambers.
             
          • krazykuda

            krazykuda Well-Known Member FABO Gold Member How-To Section Editor

            Messages:
            53,806
            Likes Received:
            18816
            Joined:
            Aug 20, 2007
            Location:
            Orland Park, IL
            Local Time:
            2:57 PM


            You could put any year 318 heads on a 64 - 65 273 and then you can use the 'standard' intake manifolds... The heads are interchangeable...

            And if you use the 66 - 67 373/318 920 heads they are closed chamber and have the later intake bolt pattern....
             
          • nm9stheham

            nm9stheham Well-Known Member

            Messages:
            12,090
            Likes Received:
            3934
            Joined:
            Dec 20, 2013
            Location:
            Waynesboro, VA
            Local Time:
            3:57 PM
            You are right... it's early in the AM after a 60 hour work week. I have corrected my post; tnx.
             
            • Like Like x 1
            • 66fs

              66fs FABO Gold Member FABO Gold Member

              Messages:
              4,833
              Likes Received:
              1522
              Joined:
              Sep 9, 2009
              Location:
              Greenwood, South Carolina
              Local Time:
              3:57 PM
              I assume you meant 273/318 heads. I would be extremely unhappy if I had an engine with a 64 head and a 69 head, or even had 69 heads on a 64 273. They might bolt on, but should be done in pairs. Your and my idea of interchangeable are different.
               
            • toolmanmike

              toolmanmike FABO MODERATOR Staff Member FABO Gold Member

              Messages:
              50,687
              Likes Received:
              35750
              Joined:
              Jan 18, 2006
              Location:
              Iowa
              Local Time:
              2:57 PM
              I gave 2 different heads on my 66 273. Sometime along the way there was a problem. One of the rod bearings was dated later as well. Oops
               
            • 66fs

              66fs FABO Gold Member FABO Gold Member

              Messages:
              4,833
              Likes Received:
              1522
              Joined:
              Sep 9, 2009
              Location:
              Greenwood, South Carolina
              Local Time:
              3:57 PM
              I have seen that many times. The worst is when chambers are different and valve/ports are different sizes. 9:1 compression on one side and 8.5:1 on the other. Dates don't bother me at all.
               
            • krazykuda

              krazykuda Well-Known Member FABO Gold Member How-To Section Editor

              Messages:
              53,806
              Likes Received:
              18816
              Joined:
              Aug 20, 2007
              Location:
              Orland Park, IL
              Local Time:
              2:57 PM
              Of course you replace them in pairs so they match... :wtf:
               
              • Agree Agree x 1
              • toolmanmike

                toolmanmike FABO MODERATOR Staff Member FABO Gold Member

                Messages:
                50,687
                Likes Received:
                35750
                Joined:
                Jan 18, 2006
                Location:
                Iowa
                Local Time:
                2:57 PM
                FYI

                #315 and #080 are both 64 and 65 273 heads. Both are closed chamber with 1.78/1.50 valves.
                #178 and #234 are 66 heads. Both are closed chamber with 1.78/1.50 valves.
                #920 are 66 and 67 heads. They are closed chamber with 1.78/1.50 valves.
                #675 are 68-69 273 and and 68-74 318 heads. They are open chamber with 1.78/1.50 valves.

                These are all casting numbers listed above and there are different part numbers listed for many of the heads so slight changes could have been made through their progression.
                 
                • Agree Agree x 2
                1. This site uses cookies to help personalize content, tailor your experience and to keep you logged in if you register.
                  By continuing to use this site, you are consenting to our use of cookies.