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Question about engine miss only when warm

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  • Question about engine miss only when warm

    I just started noticing the rebuilt engine (289) in my 1962 hawk starts missing at high RPM (say at 45+ mph). It only happens when the engine temperature gets to about 160 or more. It makes it very rough at highway speeds, though.

    The miss does not happen at the same speeds when the engine is even as warm as 140 degrees. It also is not noticeable when the car is warm, but going slower.

    The mechanic who worked on the car today says he thinks he sees evidence of arcing from a couple plug wires - one near the alternator and one near the brake booster.

    I believe the plug wires were new with the rebuild, but I vaguely recall the guy who put the engine back said the old wires were OK.

    Anyway, can arcing happen or become a problem when warm, and not when cold?

  • #2
    a lot of problems can show up when warm, but my first guess would be the coil as it is mounted right on the intake manifold.


    55 Commander Starlight
    62 Daytona hardtop
    55 Commander Starlight


    • #3
      quote:Originally posted by Scott

      Anyway, can arcing happen or become a problem when warm, and not when cold?
      Probably not, but to find out for sure, warm it up and park it in a real dark the hood, rev it a little, and watch for the arcing from the spots the mechanic indicated.

      Dick Steinkamp
      Bellingham, WA


      • #4
        What does the miss feel like? Engine smooth then sputters a little and smooths again or a surge that feels like a strong wind is hitting you square in the front?


        R2 R5388


        • #5
          Does sound like plug wire(s). It would be more evident under load.


          • #6
            The miss feels like no firing, so that there is significantly more vibration and the usual loss of power. I hear no pinging or slapping sounds, though. Also, it doesn't seem to clear up or really change. Once it starts to do it it's consistent.
            " the exception in individuals, but the rule in groups" - Nietzsche.


            • #7
              1. Weak coil
              2. Weak condensor
              3. Misadjusted points
              4. Bad plug wires
              5. Too big/uneven a spark plug gap
              6. Carbon tracking in the cap or rotor
              7. [u]Inexpensive</u> plug wires arcing on other items (including rubber products!)
              8. Loose and or dirty connections between the cap and plug wires.

              Yes arcing can show up more when warm thAn cold. It's easier for the electrical power to find an easier path to take.

              There's a few to start with.



              • #8
                Check your exhaust heat riser valve, if it's stuck closed it will force half the engine exhuast back through the intake manifold and with todays gasoline it could affect the operation of the carb. You may want to check to make sure it was installed correctly, it has to have the correct side up for it to function. Also check the distributor vacuum advance for a bad diaphram (not sure why hot or cold would make any difference, but it wouldn't hurt to check it).

                1960 Lark Convertible
                1962 Lark Regal Convertible
                Dan Peterson
                Montpelier, VT
                1960 Lark V-8 Convertible
                1960 Lark V-8 Convertible (parts car)


                • #9
                  Thanks guys. I'll try to check out as many of those things as I can. It shouldn't be anything in distributor, but you never know. I don't remember if the coil is really old or if it's new. I'll check that, too.
                  " the exception in individuals, but the rule in groups" - Nietzsche.


                  • #10
                    Question: How can I tell if I have a weak coil?
                    " the exception in individuals, but the rule in groups" - Nietzsche.


                    • #11
                      I ran across this once when a car owner replaced the points in his Lark.
                      He said it ran fine at low RPM, but at higher RPMs it began to miss. Upon closer inspection I discovered he had left out the tension spring for the points. He said there was not one in the box with the new set of points. Simple to find. Remove the dist. cap. Try to open the contact arm with your finger. It should be pretty stiff. If it's not, look real close to see if the tension spring is in place. It's shaped just like the (sometimes copper) arm the actual point contact is made onto. The tension arm should be "outside" of that arm. Look closely. Shop manual will show you a picture. If all else fails, buy a new set of points, it should be in the box. Hope this helps.


                      • #12
                        the engine miss can be electrical but make sure the tappets are not too tight adjustment is important to get right heat does expand metal of course so incorrect tappet adjustment will upset running of motor


                        • #13
                          Is this something that can get out of adjustment with about 4,000 miles on the rebuilt motor?
                          " the exception in individuals, but the rule in groups" - Nietzsche.


                          • #14
                            I'll answer that, Scott. Yeah, this could happen after 4K miles. If the valves were adjusted too tight to begin with (something that happens because the unknowing think they should be adjusted until there's absolutely NO tappet noise whatsoever)and they start to get seated from use.[^]

                            Miscreant at large.

                            1957 Transtar 1/2ton
                            1960 Larkvertible V8
                            1958 Provincial wagon
                            1953 Commander coupe
                            1957 President 2-dr
                            1955 President State
                            1951 Champion Biz cpe
                            1963 Daytona project FS
                            No deceptive flags to prove I'm patriotic - no biblical BS to impress - just ME and Studebakers - as it should be.


                            • #15
                              Heloooo Does everybody remember when I had this same problem??? Check your exhaust! Especially that riser valve.

                              Start with the exhaust. Don't make my mistake. I replaced plugs, points, condenser, plug wires, and of course the much maligned... coil. Now, don't get me wrong. After all those improvements the car runs great! But, (and she's got a broad one) The exhaust solved the problem.[^]

                              Lotsa Larks!
                              K.I.S.S. Keep It Simple Studebaker!
                              Ron Smith
                              Home of the famous Mr. Ed!
                              K.I.S.S. Keep It Simple Studebaker!
                              Ron Smith
                              Where the heck is Fawn Lodge, CA?