[flamebero]

I'm looking for part numbers for the NGK spark plugs I should be running in my '78 Spider. NGK's part finder says it is BPR7ES, but I thought I should double check.

Thanks.

 

[Tifosi]

That'll do it.
The 'R' designated resistor type, which won't hurt if you've got radio buzz, but isn't actually neccisary in the grander scheme of things.

Gap around .027"~.028"

 

[alfazagato]

My 1989 NGK specification book notes that B7ES or B7EV is the correct plug with a 0.6mm gap. I have always used the B7ES. I am also told that the projecting nose on the BP range brings the end of the electrode too close to the top of the piston and may allow arcing, I have no experience of it though.

 

[Tifosi]

The extended tip couldn't arc to the piston crown if it tried.
It's not electrically viable as the arc takes place from center electrode to ground electrode, (the ground electrode will always be closer than the piston ever could be by a very large margin), and should a plug be fouled enough to prevent that gap jump, the conductivity would revert to going through the fouling into the easiest path it could find: through the body of the plug where its threaded into the head.

However, if running hot cams there is the off chance that the intake valve can slap the ground electrode depending on lift, duration, gap orientation, valve float and revs.

 

[alfaparticle]

I have a 12.3mm intake cam and BP7ES plugs. There are no clearance problems. Maybe oversize valves could be a problem with extended nose plugs.

 

[alfazagato]

Don't know..... but but I do have a friend who holed a piston after a very fast drive to the South of France and he was told at the time that arcing was the problem. I do believe that valves can also touch the electrode under certain circumstances. As I mentioned before I do not have any experience of either happening.

 

[Elio Comello]

You may want to use the NGK Iridium version (BPR7EIX) I found them better than the "standard". Very fine electrode that will not erode and smaller ground.
Elio

 

[alfazagato]

Got to the bottom of the problem, evidently pre-ignition (French fuel?) was the start which then affected (melted?) the side electrode and thus allowed the spark to the piston crown where a neat hole was eroded. He also added that this appeared to be known problem with the 1300 engines.....has anybody experience of this?

 

[flamebero]

Sounds like I want BP7ES, thanks for checking for me!