Hi. I recently became owner of a 136 Rapid, 1.3, manufactured in 1989. According to a couple of car spares websites, my car should be fitted with NGK BP6HS spark plugs. But when I tried to fit these, the nut is too big & I can't get the plug spanner to fit . The car came with NGK BP7EFS plugs fitted.... are these the right ones to use ? I do have some running issues with the car at the moment & am trying to eliminate various things. It would help a lot knowing which plugs should be fitted. many thanks for any help...

Those are both 14mm (BP) but different heat grade (6 is hotter than 7) and thread length.

 https://www.ngk.de/fileadmin/Dokumente/EN/downloads_not_used_in_download_area/ngk_zuendkerzen_code_en.pdf

 

In fact, the one plug probably won't fit (correctly) in a mount machined for the other.

If your car is fitted with the longer plugs the electrodes will be touching the pistons at high revs because they will protrude too far.....that would cause issues! I did this once and the engine did run but closed the electrodes up and ran like a dog! Worth swapping for the correct ones......doesn't matter much if you use 6 or 7 on the heat rating.

Those are both 14mm (BP) but different heat grade (6 is hotter than 7) and thread length.

 https://www.ngk.de/fileadmin/Dokumente/EN/downloads_not_used_in_download_area/ngk_zuendkerzen_code_en.pdf

 

In fact, the one plug probably won't fit (correctly) in a mount machined for the other.

Thanks Ken.

If your car is fitted with the longer plugs the electrodes will be touching the pistons at high revs because they will protrude too far.....that would cause issues! I did this once and the engine did run but closed the electrodes up and ran like a dog! Worth swapping for the correct ones......doesn't matter much if you use 6 or 7 on the heat rating.

Thanks. The 7's are longer, but on the 6's, the hexagonal nut is bigger, & fits so close to the cylinder head, that I can't get the plug spanner around to tighten them. I guess I'll keep on using the 7's, unless something nasty happens. Just wondered what other people use....Cheers.

BKR7EIX on my race car. On my other car I have Bosch......cheap as chips and decent. http://www.ebay.co.uk/itm/4-x-Bosch-Spark-Plugs-fit-Triumph-Herald-Spitfire-Skoda-Estelle-Rapid-L87YC-/291646170256?hash=item43e7776490:g:Bn0AAOSwQoFWOMTI

 

 The 6 and 7 has nothing to do with the size of the hexagonal nut, it's an invisible heat grading.