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  #1  
Old 10-02-22, 20:05
Mark Robinson Mark Robinson is offline
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Default W670 and r975 short spark plugs

Is there a theory why the spark plugs on a w670 and r975 engines are a lot shorter than the thread in the heads?
Most spark plugs I have come across use the full thread and protrude into the combustion chamber.
Have come across fairly heavy carbon build up on the threads more than once? On both the w670 and r975.
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Old 10-02-22, 20:39
Jesse Browning Jesse Browning is offline
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I don’t remember that being the case.
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Old 10-02-22, 21:30
Bob Phillips Bob Phillips is offline
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A Longer thread protruding into the cylinder, if clogged up with carbon, would be very difficult to remove.
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Old 10-02-22, 21:38
Mark Robinson Mark Robinson is offline
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Yes I can get to that but why not the same thread length ?
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Old 10-02-22, 22:01
Mark Robinson Mark Robinson is offline
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The NGK AS-6 shielded plugs I have removed from the w670 engine has a thread length of 8.46 mm to the crush washer but the threaded hole for the plug has a thread length of 14.41mm so the electrode of the plug is within the confines of the hole not protruding in to the combustion chamber ?
On the six w670 engines I have worked on all plugs have this shorter plug thread to head thread length!
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Last edited by Mark Robinson; 11-02-22 at 22:07.
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