Spark Plug threads size

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Old 10-08-09, 09:36 AM
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Spark Plug threads size

Looking for a reference for spark plug thread sizes/pitch...

Ariens push mower purchased at a Box store, was a return and sold az-is.
Kohler courage XT-6 engine.
Complaint was that it would miss and sputter after 15mins. First time I have seen one of these with the full auto choke. I lightly tried to pull the engine through (just a habit) and it fired right up (and it was a cold morning) so I mowed with it for 10 minutes or more and the thing never let up once even in deeper wet grass. So I clamped the bail and let it run expecting it to run out of gas soon, which it did not do for another 15 minutes at which time I was about to give up finding a problem to diagnose. When I started it back up, sure enough, spit, miss, sputter...Pulled the airfilter housing to observe the choke and even manual movement made no difference.
Oil was slightly overfilled so I drained it, found speckles in the oil. Dropped the bowl on the carb to find it spotless. Checked the needle valve operation and it seemed flawless, operating just as it should. Pulled the plug and it looked great, tad of white but not bad at all. So I am thinking valve adjustment and leave the plug out to go see if I can find a manual which I do on the kohler site. Next morning I check the valves and they are right on. So I figure put it back together see if I can repeat the problem and do some more trouble shooting. Went to install the spark plug, by hand (always) and it got snug after 3 or 4 turns...so I back it out, inspect the plug threads, which are fine, inspect the threads in the head and see they are stripped/crossed...the plug that was installed is a NGK D7EA so traipse back to house to find out what plug is called for. Champion RC12YC or equivalent, found that NGK equivalent is BCPR5ES. Found one of each of the called for plug and compared to the D7EA that I found installed, and it sure seems to me that the D7EA is not only smaller size but also courser pitch.
Neither of the plugs that should fit even offered to start threading and now I am wondering if its possible the head is not tapped for the right plug.
I talked to the customer and informed him of my findings and asked if he had by some chance checked the spark plug...he was absolute that he had not and whatever was there was just as it was when he bought it.
I felt strongly that he had a case to make some noise about before I tore into. He originally wanted it back yesterday when I found this and now will be out of town for a week or so, so I have some time.
My com padre sometimes employer couple of hollers over, is vacationing on the coast so my kohler connection is not available...

Reference of spark plug thread sizes, thoughts, ideas or comments appreciated...
 
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  #2  
Old 10-08-09, 02:38 PM
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When something similar happens to me I take the plugs/bolts or whatever to the local hardware store and find the nut that will thread onto them then check the specs for the nut. Have a good one. Geo
 
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Old 10-08-09, 06:34 PM
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The Champion RC12YC has a thread diameter of 14mm and 1.25mm pitch.

The NGK D7EA has a thread diameter of 12mm x 1.25mm pitch which is smaller than the Champion RC12YC thread.

If the hole is smaller than 14mm then there is no doubt the hole was tapped for a 12mm plug.

I would just tap it to 14mm x 1.25mm and let it go.

Holler huh, sounds like Tennessee!
 
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Old 10-08-09, 08:18 PM
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Thanks Airman, thats what I was looking for. If it is tapped at 12mm have to dig out the thread chart for drill size.

I had an ole Arky buddy used to say holler bout what its like up here though, cept bigger
 
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Old 10-08-09, 08:22 PM
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Originally Posted by geogrubb View Post
When something similar happens to me I take the plugs/bolts or whatever to the local hardware store and find the nut that will thread onto them then check the specs for the nut. Have a good one. Geo
I do the same on a regular basis geo thx
 
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Old 10-14-09, 12:24 PM
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The threads were indeed 12mm x 1.25 and cleaned up very easily. Since this was an "asis" purchase and already a bastage machine I let it go there rather than worring about an STC
 
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