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    What do these spark plugs tell me?

    Some may recall that I've had ignition problems and, during the course of the investigation, I noted that spark plug 3 was in a horrendous condition - completely covered in "coke" (carbon).

    I now seem to have sorted the ignition problems, but am not so happy with the engine, as it makes the impression it's firing on less than 8 cylinders smoothly.

    Thought I'd check the spark plugs and, low and behold, that No. 3 is again starting to get black - followed closely by its bedfellow No. 5. I checked the comnpressions (annotated in bar on the attached pic)but couldn't find any correlation to the spark plug condition. The only coinciding factor between cylinders 3 & 5 is that they are both fed by the LH Carburettor (but then so are 2 & 8 and those plugs appear to be fine)

    I do notice now on the pic, that the plugs 3 & 5 have the entire thread oily, whereas the others don't.

    Any ideas?

    Drew

    Spark Plugs.jpg ,
    The answer isn't 42, it's 1/137

    #2
    Is it just an optical illusion that plugs 3 & 5 seem a bit longer in the length of the threaded section?

    Possibly worth fitting a new plug lead and new plug on #3 (possibly a different rotor on your EI) and see what happens performance-wise and a future plug check.

    Otherwise, from this information, I haven't a scooby
    White 1976 build ("Mk2") only a few mods

    Comment


      #3
      #’s 1, 2,4, and 7 all “look” like they have old threads in them. Do they?

      if so, you’ll need to install threadserts of your liking. I prefer Timeserts, but many are happy with Helicoils.

      Cyl #3 looks like it’s not burning all the fuel, so as Jonno said, check the spark plug lead, make sure it is fully seated etc.
      Attached Files
      John

      Comment


        #4
        As John says I would make sure that the plugs are seating/sealing properly. Look at the plug hole and the seating area, any evidence of leakage there? You could fit the plug and put some soapy water (leak detector" around it and turn the engine over by hand (use a spanner!) until No. 3 is up on compression/firing stroke and watch for any leakage/bubbles etc.

        To rule out the spark plug and lead I would clean them up and swap no.4 plug and lead with no. 3 (obviously move the leads in the distributor), then run it and see if the "effect" stays with no.3 or moves to no. 4.
        White TV8 BW35 no mods and now a Dolly Sprint to keep it company
        So many cars, so little time!

        Comment


          #5
          I would suspect oil getting down the valve stems and dodgy seals. However I have never seen under the rocker box covers, so may be completely off track.

          +1 on the thread lengths of the plugs appearing different.

          Comment


            #6
            The thread lengthes appear different - for some reason, oil seems to be able to creep up all the thread on the "good" spark plugs, but not on number 3&5. The plugs themselves screw in full and seat exactly as their neighbours, Plug leads have been completely changed in my previous hunt for the ignition problem, but the problem plug is still No 3.

            I could check the seating of the plugs, but the fact that the compression tester produced correct results seems to indicate that the thread in the head is ok, The plugs are all brand new, and the older plug which had carbon build up was also No. 3, so I can't believe it's the plug. Too much oil getting in sounds like a possibility, but I can't think how I could narrow that down short of taking heads off. I guess I'd have to be looking at cam followers and wear, non?
            The answer isn't 42, it's 1/137

            Comment


              #7
              I just pulled my plugs as well, no issues to speak of but also had oil on the threads, all 8. I do use a little hi-temp anti seize which is black but pretty sure it was oil.

              Interestingly I opened the gaps up from 25 to 35 which my pertronix and uprated coil should allow and the popping on deceleration I have definitely reduced, indicating a better burn.. so wonder if playing with your gaps would help with isolating this issue? Wide gaps will spark a bit better but seek out issues in the hv side, narrow gaps will not have as big a spark but be kinder to any weak components on the hv side.

              Terry
              Last edited by trunt; 4 July 2022, 20:56.
              Terry Hunt, Wilmington Delaware

              www.terryhunt.co.uk

              Comment


                #8
                The ceramic looks very white on most of those plugs, it could be they are very new or it could be the misfire is an overly weak mixture.
                I have noticed oily threads on some of my engines. I suspect the sealing washer isn't doing a perfect job but the plug colour isn't affected by the oilyness of the threads
                Neil
                TV8, efi, fast road cams and home built manifolds. 256bhp 240lbft torque

                Comment


                  #9
                  Originally posted by flying farmer View Post
                  The ceramic looks very white on most of those plugs, it could be they are very new or it could be the misfire is an overly weak mixture.
                  I have noticed oily threads on some of my engines. I suspect the sealing washer isn't doing a perfect job but the plug colour isn't affected by the oilyness of the threads
                  Good point, I did order new bp5e plugs from UK (they seem to be unavailable in USA) as mine have been in and out quite a number of times now and the seal is probably crushed.
                  Terry Hunt, Wilmington Delaware

                  www.terryhunt.co.uk

                  Comment


                    #10
                    The plugs are indeed brand new and have only done about 80km. I was also surprised at how white they are - above all because the journeys I have been doing have been between villages in the neighbourhood and down to the shops. I was expecting to find them completely sooty. On two of them there is even a little brown spot - which I understand is a sign of overheating. I previously had Champion, now NGK's are in.

                    During the search for the ignition failure I didn't touch any carb settings - only changed the float valves.

                    Concerning the black plug, it occurred to me after switching off the PC yesterday that I have a noticeable tick-tick.tick from the engine after starting and idling. It goes away after a few minutes. Could I be looking at one or two worn cam buckets, which are letting some oil past?
                    The answer isn't 42, it's 1/137

                    Comment


                      #11
                      Originally posted by dasadrew View Post
                      The plugs are indeed brand new and have only done about 80km. I was also surprised at how white they are - above all because the journeys I have been doing have been between villages in the neighbourhood and down to the shops. I was expecting to find them completely sooty. On two of them there is even a little brown spot - which I understand is a sign of overheating. I previously had Champion, now NGK's are in.

                      During the search for the ignition failure I didn't touch any carb settings - only changed the float valves.

                      Concerning the black plug, it occurred to me after switching off the PC yesterday that I have a noticeable tick-tick.tick from the engine after starting and idling. It goes away after a few minutes. Could I be looking at one or two worn cam buckets, which are letting some oil past?
                      Did the installed height of the floats change with the new float valves? Its possible the level is a bit lower which would weaken the mixture, particularly if the old valves were leaking fuel and giving a higher than expected level in the float chamber.
                      Can't say I have noticed any correllation between worn buckets and oil consumption as the bucket acts like an umbrella over the valve spring. It is possible that a worn bucket might put more of a side load on the valve which would accelerate wear of the valve stem and guide. This would lead to greater oil consumption on the affected cylinders
                      Neil
                      TV8, efi, fast road cams and home built manifolds. 256bhp 240lbft torque

                      Comment


                        #12
                        To be honest, the float valve problem I had was a very unwelcome perturbation to the real fault (ignition) that I was trying to tie down, so I popped new valves in without doing a new float set-up procedure, just to get the engine running again. You're right, now I've got the Stag running again I should go back in to the carbs and check the float heights - thanks for the reminder!

                        I wrote above that I'd replaced the Champions with NGK. In fact it was the other way around, so I'm now running Champion plugs which - according to the box - should have a 0,8mm gap - which I haven't changed to match the ROM figure.

                        I've now put all back together and will observe the plugs for a while to see if they start to become brown rather than white with brown speckles!
                        The answer isn't 42, it's 1/137

                        Comment


                          #13
                          Have never had a good experience of champion plugs in my stag.
                          Always ok with ngk though.
                          There are 2 secrets to staying on top :- 1. Don't give everything away.
                          2.

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