NGK BP5ES Spark Plugs

[RAY]

I know there has been a fair bit written about these plugs here before but just wanted to share and maybe get an answer to my current experience.

As these plugs had good reviews of people's experiences with these plugs i purchased a set and swapped my existing Bosch WR7DC's and not having my manual to hand when i did this, gapped them the same as the WR7DC's, 0.060, which at the time i thought was bigger than any spark plug i had gapped before.

The engine started immediately on the button, drove it for around 80 miles, mostly motorway, and it ran like a dream, better than ever.

A few days pass and i check the manual for the correct gap and realise it should have been around 0.030 so today i re-set the gaps and straight away the engine does not start as well and runs very ' lumpy ' so I let it warm up and take it out. It's terrible, unresponsive, won't tick over smoothly, still very lumpy and if i stop in drive mode it barely ticks over. So the gaps get changed back to 0.060 and it's a dream again.

Has any one else had to set there plugs at such a large gap and why does mine need to be 0.060 ?

It's a 280 Auto with 123 Ignition USA model.

Ray

[alpina]

Hi Ray,

I changed last year https://www.sl113.org/forums/index.php?topic=29693.msg215012#msg215012

gapped at 0.9mm and runs great.

[ja17]

Sounds like you may have gotten a plug wire switched wrong? FYI even the Mercedes_Benz Factory uses NGK spark plugs in some of their newer models when new.

[RAY]

Hi Joe,

Definitely no crossed wires, only ever do one plug at a time, then replace the lead. No confusion that way.

Alpinaltd
I believe 0.9mm equates to around 0.035 so still a masive difference.

[ja17]

It should not make that much difference anyway. You might want to do a check on each spark plug wire, to make sure the ends are tight. What are the condition of your wires? You may want to check each lead for resistance. You may have a resistor end going bad. Are your using a hotter than stock coil? Make sure your spark plug wires and coil wire are not "carbon type". I normally use .028" to .030" for gap. Are your spark plug connectors 1 ohm or 5 ohm ( they are marked on the metal side of the connector).

[ja17]

Depending on the condition of your ignition system and how it is set-up (resistances, resistors, coil etc.) it may or may not be able to cope with a much wider spark plug gap.

[Paul & Dolly]

Ray

Mine is UK car,  early 250SL, I changed to NGK BP5ES (from BP7ES) two years ago, they are gaped to 0.8mm, 123 Distributer, Red Coil, all works well.

Paul