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 D500 hemi "Mystery" miss cause, found and correctedJump to page : 1 Now viewing page 1 [50 messages per page] | View previous thread :: View next thread |
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56D500boy |
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Exner Expert 10K+ Posts: 11182     Location: Lower Mainland BC | . For the past few weeks I have been trying to dig myself out of "hole" that I created by reusing a 9 year old cork D500 hemi valve cover gasket. Applying red RTV on the old gasket did not work. It leaked badly. To investigate a hemi ("double rocker for the purists) valve cover gasket, it is necessary to remove the spark plugs and tubes. Once the gasket has been dealt with, it is necessary reinstall the spark plugs in their metal tubes. The prescribed method of doing that is to install the plug into the tube and then lower the assembly, with the spark plug socket (and extension) through the valve cover and into the well in the head "do not drop the spark plugs into the tubes as this may cause the gaps to close up. When installing, place a spark plug in the socket wrench (Fig. 37) and bring the tube down over the plug. Hold the plug down in the tube and insert the assembly into the cylinder head." I know this and have always loaded the spark plug into the socket, holding the socket vertically and then shoving (gently) the plug upwards into the tube, rotating the plug wrench to bring the spark plug threads fully through the tube. So there should NOT have been a problem re-installing the plugs back into the head. *HOWEVER*, in my case, the No. 8 plug (passenger side head, right at the firewall end of the head), I have a conflict with the transmission dip stick tube making it awkward to insert the assembly through the valve cover. When I was re-installing the spark plugs yesterday (after yet another attempt at sealing the valve cover gasket), I checked the gap on the plugs as I reinstalled the assemblies. No. 2 = fine, No. 4 = fine, No. 6 = fine, No. 8 = WHAT THE HECK?? No gap (or very very little). No gap = no spark = miss. In retrospect, I must have dropped the No. 8 assembly through the valve cover in a manner that caused the spark plug electrode to bump into the hard metal of the head, causing the previously set gap to disappear. So the solution was easy: Re-gap the spark plug and re-install in the tube, very carefully. Result was the next time (a few minutes later) that I started the engine, the "mystery" miss was miraculously gone. Goes to show you (me) how little things are important. Edited by 56D500boy 2026-07-12 11:15 PM (55ChryslerFSMSparkPlugInfo_2.jpg) Attachments ----------------  55ChryslerFSMSparkPlugInfo_2.jpg (185KB - 34 downloads) | ||
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