I'm not 100% sure it is causing any damage. But by reading and compare the "Part Numbering System" http://www.ngkspark.com.au/sparkplug.php# . They have the same thread diameter (14mm), thread lenght (19 mm), Spark gap (1.1mm), resistor, only the different is heat range (BKR6E-11 is 1 level colder). So I think it did not cause any damage.