One Spark Plug Longer Than The Others???
01-29-2019, 04:20 PM
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One Spark Plug Longer Than The Others???
(1989 L98) I was changing my spark plugs, and noticed that the cylinder number 4 spark plug was longer than the rest. Then when I tried putting the new plug in there (AC Delco Rapid Fire) it would not screw into place no matter how much I tried. Then when I put that old, longer one in there, it screwed right into place. Any ideas of what’s going on???
01-29-2019, 06:38 PM
#3
Brand and part # of the ODD one and which part # RapidFire did you buy?
01-29-2019, 07:03 PM
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01-29-2019, 07:45 PM
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(1989 L98) I was changing my spark plugs, and noticed that the cylinder number 4 spark plug was longer than the rest. Then when I tried putting the new plug in there (AC Delco Rapid Fire) it would not screw into place no matter how much I tried. Then when I put that old, longer one in there, it screwed right into place. Any ideas of what’s going on???
All 89s have aluminum heads I believe. If the threads are really different, more than likely someone stripped the threads and installed a threaded sleeve to replace them. Either the sleeve has with different/wrong threads or the sleeve itself came out when you unscrewed the plug (and is still on the plug).
If it is in fact a sleeve with different threads the easiest thing to do is cross reference the plug you took out to get a replacement for that cylinder.
Last edited by auburn2; 01-29-2019 at 07:53 PM.
01-29-2019, 08:27 PM
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They do not have different threads in different cylinders. The OEM plugs should be AC FR5LS, so the one that is in there is not the plug it calls for.
All 89s have aluminum heads I believe. If the threads are really different, more than likely someone stripped the threads and installed a threaded sleeve to replace them. Either the sleeve has with different/wrong threads or the sleeve itself came out when you unscrewed the plug (and is still on the plug).
If it is in fact a sleeve with different threads the easiest thing to do is cross reference the plug you took out to get a replacement for that cylinder.
All 89s have aluminum heads I believe. If the threads are really different, more than likely someone stripped the threads and installed a threaded sleeve to replace them. Either the sleeve has with different/wrong threads or the sleeve itself came out when you unscrewed the plug (and is still on the plug).
If it is in fact a sleeve with different threads the easiest thing to do is cross reference the plug you took out to get a replacement for that cylinder.
01-29-2019, 09:31 PM
#8
Safety Car
(1989 L98) I was changing my spark plugs, and noticed that the cylinder number 4 spark plug was longer than the rest. Then when I tried putting the new plug in there (AC Delco Rapid Fire) it would not screw into place no matter how much I tried. Then when I put that old, longer one in there, it screwed right into place. Any ideas of what’s going on???
It'll take someone with a lot of talent to install a helicoil in the head without removing it from the engine!
02-02-2019, 10:47 AM
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Last edited by 89’Vette; 02-02-2019 at 10:49 AM.
02-02-2019, 12:40 PM
#13
Race Director
Just put in a new set of ac delco 41-627 plugs and call it a day.
02-02-2019, 08:13 PM
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Drifting
02-02-2019, 10:30 PM
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02-03-2019, 08:30 AM
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Based on the information posted, it seems you haven't isolated that it is the plug or head.
Spark plugs are a manufactured product. Manufacturing works on Statistical Process Control (SPC) where a 1.67CpK is acceptable. This means 99.7% of parts manufactured will have a dimension that is within tolerance, per dimension. Meaning, on any given part there is a .3% chance you will have an individual dimensions. I will stop the math there, if anyone wants to do probabilities go ahead. My main point is there is always a chance a part could be bad. Seems the plug would be the unknown and your head should be known given it had a plug in it before.
I may be off if I missed something you did to isolate the problem.
02-03-2019, 08:58 AM
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Just out of curiosity, the plug that didn't fit in #4, did you try it in another cylinder? Did you take a plug that fit in another cylinder and it too wouldn't go in #4?
Based on the information posted, it seems you haven't isolated that it is the plug or head.
Spark plugs are a manufactured product. Manufacturing works on Statistical Process Control (SPC) where a 1.67CpK is acceptable. This means 99.7% of parts manufactured will have a dimension that is within tolerance, per dimension. Meaning, on any given part there is a .3% chance you will have an individual dimensions. I will stop the math there, if anyone wants to do probabilities go ahead. My main point is there is always a chance a part could be bad. Seems the plug would be the unknown and your head should be known given it had a plug in it before.
I may be off if I missed something you did to isolate the problem.
Based on the information posted, it seems you haven't isolated that it is the plug or head.
Spark plugs are a manufactured product. Manufacturing works on Statistical Process Control (SPC) where a 1.67CpK is acceptable. This means 99.7% of parts manufactured will have a dimension that is within tolerance, per dimension. Meaning, on any given part there is a .3% chance you will have an individual dimensions. I will stop the math there, if anyone wants to do probabilities go ahead. My main point is there is always a chance a part could be bad. Seems the plug would be the unknown and your head should be known given it had a plug in it before.
I may be off if I missed something you did to isolate the problem.
Yes I did. The plug that didn’t fit, did fit in all the other cylinders. And it was the 2nd time I tried putting a new plug in there (Rapid Fire 5)
