[928uk] 928 S2 service parts

[Paul R Smith]

 From Bosch: "Heavy duty yttrium-enhanced center electrode with copper 
core provides superior reliability and durability. Tapered cut nickel 
chromium ground electrode assists in cold weather starts and provides 
increased ignitability."

As to the gap, the gap is set for the engine. Very generally,  old 
engines with magnetos often had gaps of 0.5mm (20 thou) or less (15 or 
18 thou). 25 thou became standard with battery/points/coil ignition and 
that has got rounded up to 0.7mm with metrification and the change to 
electronic ignition.
All 928s have electronic ignition which could cope with much larger 
gaps, but the spec is set taking into account lots of things, and 
Porsche settled on 0.7 with the tolerance to 0.8, probably to allow for 
badly worn or fouled plugs to still work well.

For Bosch to put 0.8 on the box, I suspect is a marketing decision. 
"These fancy plugs will give you a bigger spark!".

Electronic ignition is so capable that for a new plug out of the box I 
just look at the gap to see that it hasn't been damaged in transit, if 
it looks about right, it will be fine.

Smiffy

On 13/06/2024 22:51, jonathanrackowe--- via 928uk wrote:

Well apparently those WR7DC+ are the replacement for WR7DC; they have a different central electrode material. They're fine, but the box says their gap is 0.8 while the Porsche spec is 0.7 +1, so because plug gaps widen with use I would set the gaps to 0.7 with a metric feeler gauge and a proper spark plug gapping tool. Don't ever touch the central electrode, it's easy to damage it. A spark plug gapping tool allows you to carefully bend the outer "ground" electrode away from or towards the centre electrode. Now is someone going to tell me that re-gapping them is wrong because the new electrode material needs a larger gap?

  

Nothing wrong with having 2 spare spark plugs. Put them in your rear seats glove box alongside the spare bulbs, spare fuses, spare 141 951 253 B relay, and fuel pump relay jumper wire 😊

  

Best regards,

Jonathan

  

1991 928 GT Amethyst Metallic