Dart Oily Plugs

[classiclife]

Hello David,

The "5" plug is slightly hotter (softer) than a "6".

"Y" means your centre electrode is grooved with extra protection - what the extra is I cannot recall at the moment.

With regard to the .030 setting, I think that is too wide if your engine is not burning oil. Classic car owners who do suffer oil fouling on plugs quite often enlarge the gap and I wonder if the PO has done this either because there is an oil fouling issue OR thought there may have been due to the presence of oil in the tubes.

Have to say the NGK BP6ES is running well for me and it is a plug that works well across the heat range; I have set my gap at .025 as recommended by Daimler.

Ironically, NGK state a B5ES for the 2.5 and 250 range but the BP6ES seems to do just as well and offers flexibility as mentioned throughout the heat range.

FYI the "P" stands for protruded nose, which as has been mentioned elsewhere is probably more beneficial for combustion due to the shape of the chambers.

Hope that assists, somewhat.

I have also included a NGK link which is very informative; in fact by NGK Australia: https://www.ngk.com.au/products/spark-plugs/

Best wishes.

Richard.

[faeton]

The copper seals for the bottom of the tubes are advertised by David Manners in the latest Driving Member Magazine . £1 32p each.. part no 433742 , I have always thought that this type of seals are a bit flimsy , as they have to line up with the bottom of tubes a wider copper washer may be more suitable? , Dave

[Ian Slade]

Couple of points ( no pun) on the last two posts, if electronic ignition of any type is fitted it is normal to increase the plug gap upto 50 thou", problems with the points can occur if the plug gap is increased with the standard two point set up.
With the copper "O" rings, fit the largest size possible, it is a well known fact the motor industry will specify the cheapest component capable of carrying out the task, even Daimler and certainly Jaguar in those days. Copper seals and "O" rings are probably one of the most profitable items for any parts department, they are available from many engineering supply companies and outlets for the odd few pence.

[captain bobo]

Please pardon my ignorance Ian, why is it good practice to open the points gap to around 50 thou for electronic ignition? What does it achieve?

[Ian Slade]

You get a larger spark so a more instantaneous burn, OK it's measured in milliseconds but every little helps and supposedly it's a cleaner burn, being electronic there is a higher Wattless voltage to the coil thus a higher HT voltage at the spark plug. The so called high performance coils have better insulation that can cope with the higher voltages for longer or so the marketing blurb says.

[tjt77]

sealing the plug tubes ( should it be deemed necessary ) is relatively striughtforwrd as long as one adopts the approach of everything being squeaky clean (absolute cleanlinss almost impossible 'in situ') commonly the copper washers have damage due to overtightning..I replace then with new as a matter of course if doing a top end overhaul.. there is a small chamfer in the head surrounding these tubes.. my method is to screw the tubes in to within 1/4" of being fully tight..then place light bead of silicon gasket maker evenly around the base of tube sufficient to fill the chamfer..and then cinch up tight.. this prevents oil from entering the threads.. resolving a potential problem from arising..