Something In my #5 Cylinder?

Small Block Mopar Engine

  1. Walker434

    Walker434 Well-Known Member

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    Hey guys, I'll give a little back story on my build then copy and paste what I had put in my thread on the Forced Induction Section.

    71 Dart Street/Strip. 360 block bored .060 over with a 4 inch crank making it 414 cubic inches. Aluminum Indy T/A heads. This was built for boost so its right at 9:1 compression. Running a Procharger with 10 lbs of boost. Blow through carb. See below for what happened.

    Okay guys, the last pass I made down in Alabama the car slowed down a bit. I had hot lapped it so I didn't think much of it. The Next day when I was unloading the car off the trailer it was missing. I pulled the plugs and the #5 cylinder's spark plug looked like the picture below. Ground strap had been punched into the electrode. I borrowed my friend's bore scope and there was evidence that something had been in the cylinder but was no longer there. We checked the compression and it was good, same as the other cylinders. Can't figure out what could have gotten in there. Carb looks normal, hat, ect. I checked every tooth on the procharger…. everything looks good. I checked the vale lash and all was normal.

    So, I thought it must have somehow sucked something in that cylinder but then spit it out the exhaust valve. I swapped to colder spark plugs and have been driving on the street a few days with no problems. However I have been driving like miss daisy not getting on it. Since racing season is over around here I decided to get on it yesterday to see if I still have problems. Sure enough, heard a pop on the 1-2 shift and shut it down. It was missing. Limp back to house and once again my #5 plug had the ground strap mashed into the electrode.

    Any ideas? If it were the piston hitting the plug would the scars on the piston be in the same place? Could something still be in that cylinder I just haven't seen it with the bore scope? You would think if something were in the cylinder it would be loud at idle. This thing sounds completely normal at idle and low RPM. I'm baffled. I'm going to bore scope it again but If I can't find anything I guess I'll pull the engine back out and inspect everything.
     

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  2. GEO

    GEO Sarcasm Inc.

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    My first thought would be that part of the piston broke off
     
  3. abdywgn

    abdywgn dismantler

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    Watching. Something somewhere. Are there any parts of the spark plug missing? Melted away that are causing the problem. If it was on the intake side, wouldn't the supercharger be ingesting it first and then it would be having problems?
     
  4. Walker434

    Walker434 Well-Known Member

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    I have bore scoped it and the piston didn't appear to have any part broken off. This is an exterior, belt driven procharger.

    Dart 31.jpg
     
  5. Walker434

    Walker434 Well-Known Member

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    No part of the spark plug is missing. It actually looks really healthy just no gap. The ground strap has been pushed into the electrode.
     
  6. MOPAROFFICIAL

    MOPAROFFICIAL Well-Known Member

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    I'm not downloading anymore pictures.
    Just post the pic, skip download links.
    Ate a bit of the turbo, impeller, maybe.
    Porcelain came apart, maybe, bits lined up between piston and plug tang, maybe.
    Something from the carb came loose went through, now the tune is off and running poor. Maybe.
     
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    • yellow rose

      yellow rose Doctor of Thinkology.

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      I can't imagine at that CR the piston is anywhere near the plug. For that to happen, something went wrong.

      Most likely, something came off of the PC or the carb or maybe your intake system can pick up a rock or something and it found its way into the engine and found a home in the number 5 cylinder.

      It's gone now, so you may never know what it was. But most likely, you have hurt that Rod bearing enough that as the RPM,s go up, the piston can come up and smack the ground wire.

      You could index the plug...but you ain't fixing the issue.

      You can hurt a bearing enough to close up the gap on a plug and not make noise. BTDT many times.

      Your engine is telling you something. Get a handle on it before it eats your wallet.
       
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      • yellow rose

        yellow rose Doctor of Thinkology.

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        Beat me by a gnats eyelash!!!!
         
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        • furrystump

          furrystump Well-Known Member

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          With the valves closed and the spark plug out put air gun nozzle into spark plug hole place a rag to try and catch any piece. Might blow any debris out if there is still something in there. Just spit balling
           
        • TrailBeast

          TrailBeast Slightly Twisted Member

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          Also keep in mind that just because whatever it was, was in that cylinder doesn't necessarily mean it originated from that cylinder.
           
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          • furrystump

            furrystump Well-Known Member

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            Maybe a screw in air bleed backed out.
             
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            • yellow rose

              yellow rose Doctor of Thinkology.

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              Yup...I forgot to mention that. I had a 1/2 wrench go through one of my engine. Hit 2 cylinders on both sides.

              What happens in a running intake tract is stunning for sure.
               
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              • yellow rose

                yellow rose Doctor of Thinkology.

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                Certainly possible.
                 
              • MOPAROFFICIAL

                MOPAROFFICIAL Well-Known Member

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                Ring land,
                Already said that.lol read the replies!
                 
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                • Davezilla

                  Davezilla Member

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                  I am not an engine expert, but if it was a damaged rod bearing causing the piston to contact the spark plug as mentioned earlier, wouldn't there just be one mark on the top of the piston? The picture shows damage all over the top of the piston, which seems to indicate something was moving around in the cylinder.
                   
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                  • yellow rose

                    yellow rose Doctor of Thinkology.

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                    I'm saying something got in there and it was getting smacked around. You have zero clearance when something is getting smashed between the piston and the head. And the Rod bearing takes all that load.

                    It doesn't take long beating on a bearing like that before it develops some extra clearance. Not enough to make noise, but enough to let the piston punch the spark plug right in the mouth!
                     
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                    • Demonracer

                      Demonracer 71 Demon 00 Ram 16 Chrysler 300S 05 Caravan FABO Gold Member

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                      IMHO, I'd pull the cylinder head & check the inside of the cylinder as well as the top of the piston. I would also roll the motor over by hand a few times just to see what might be happening. Just my .02.
                       
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                      • Davezilla

                        Davezilla Member

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                        Thanks for the clarification. Now I understand what you are trying to say. There was something loose in the cylinder first, which damaged the top of the piston and the rod bearing, then the damaged rod bearing allowed the piston to contact the spark plug, which closed the plug gap.
                         
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                        • rustycowll69

                          rustycowll69 Well-Known Member

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                          have a look see at the carb throttle blades. Years ago, I had a brand new Carter 500 lose all 4 primary screws retaining the throttle blades to the shaft.
                           
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                          • j par

                            j par Well-hung Member

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                            If it's down for the winter I very much like the idea of pulling the head...
                             
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                            • Garrett Ellison

                              Garrett Ellison Amateur driver on public roadway, do not imitate..

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                              Possibly even a chip off of a hardened valve seat, high temps from boost and possible detonation can cause that very problem. Definitely time to pull the head, a valve seat that is attempting to come out will junk out an engine in a heartbeat...
                               
                              Last edited: Nov 5, 2019
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                              • T56MaxTorq

                                T56MaxTorq Well-Known Member

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                                What do the other cylinders look like with the scope?
                                 
                              • mbaird

                                mbaird mbaird FABO Gold Member

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                                Pull your carb .. flip it over and count the baseplate screws .
                                 
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                                • Oldmanmopar

                                  Oldmanmopar Going left turning right FABO Gold Member

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                                  I had a piece go through the super charger no screen, Bent the electrode. Cylinder stopped firing so we pulled the plug. Couldn't see anything in the bore with a scope. It put a couple nice marks in the piston. Pulled the head and there was a piece of metal smashed and stuck in the head. Glad we pulled the head.
                                   
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                                  • stixx

                                    stixx Well-Known Member

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                                    What is the average distance of a spark plug to the piston at TDC? For sure less than one of the valves when open. So no way in hell the rod bearing can devellop that much clearance as to let the piston hit the spark plug. A loose bearing can be heard when it's out by ... 0.01"? Sure the spark plug is farther away than that...

                                    Otherwise... what oldmanmopar said: something broke off somewhere and went through cylinder #5.
                                     
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