Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Workshop Note - Roadster S1 Spark Plug Inspection

My handbook said a gap of between 1.27 - 1.30mm. The plugs I bought which are supposedly suitable for the engine were gapped to 1.10mm. I increased the gap to 1.28. I'm sure the plugs are suitable for other engines with a different required gap, so went for the recommended increase. Hopefully I'll have no issue as the plugs under the manifold are a pain to get at.

Iridium, Platinum and Gold Palladium fine tip plugs spark at a lower voltage so could accept higher gaps without extra loading on coil packs. Could explain these wider recommended gaps.

I could be wrong, but the plugs I took out were standard copper tipped. All my research shows the gap should be 1.30mm for the engine but I would have thought the gap should depend on the plug to ensure a good spark, but I'm not that knowledgeable on how things work.

Plug gap will be optimised to provide a meaty enough spark to give reliable fuel ignition and burn, and also to ensure the spark jumps the gap reliably and with minimal jitter. At normal atmospheric pressure air breaks down between two smooth metallic hemispheres at around 30kV/cm. Shaping the electrodes to say a fine point will increase local field strength and enhance spark initiation. Reducing the gap will enhance spark initiation. Higher engine compression (gas density) will hold off sparking for a given voltage. When I rebuilt a Ford Xflow to race spec’ I had to reduced the gaps to obtain good ignition performance at the higher compression ratio. If the gap is too large for the spark to jump it will find another route. If it tracks in the ignition coil it will soon produce a preferred path there and hence damage the coil. So, the biggest possible gap is not necessarily the best choice. Conversely too small a spark may not produce a full burn.

Think I actually understand that. So maybe it's a bit of both, engine requirement, but also depending on the type of plug?

Just a quick bump on this subject.

At 26,100 miles, maybe it is time for a plug change. I've only examimed my Roadster plugs once before, back in 2018. So on Saturday I fitted, as mentioned up in this thread, NGK Laser Platinum PTR 6F-13 7569 plugs.

Nearside are simple enough. All came out easily. In fact, somehow the access and replacement was easier than the Duratec/GDI. I think that the narrow access tubes on this engine reduces the risk of cross threading.

The offside is challenging. You don't need to remove the inlet manifold completely, but it does need unbolting and lifting, and some attachments must be disconnected to get the height. What also matters is an extension piece to the plug socket which is just long enough to fit, but not too long to make it impossible to lift out.The inlet manifold gasket is one of those turquoise neoprene contoured assemblies, which locates in a groove in the block, and so stays put. And it's now coped with two removals of the manifold.

So, if you do this, first get an extension piece to your socket set, which just shows over the top of the head when the plug socket is engaged. A 7/16" drive, or even smaller will work better than a 1/2".

On re-assembly, its all about locating the fixings by hand, and by feel. The two shorter fasteners hold the manifold vertically. It's imbalanced because most of the mass is offside. So first clunk it down into place. There are no obvious dowels for location. Next insert the two horizontal small fasteners by hand only, and juggle the alignment until they go all the way by hand. Don't nip up yet. Then replace the vertical fasteners. Two fasteners also locate the top coolant hose. Each one should go back in easily by hand. When they are all in place, nip them up progressively, but not sequentially from one end. No doubt there is a prescribed order in some manual, but just use common sense and don't overtighten. Like the plugs, this is a feel and experience thing. I would expect both to be low figures, in the 10/12 lb ft zone but don't quote me on that!

FWIW: I use the same plugs in my 2 litre Duratec engine.

I change my plugs every service ie yearly. I know it's not necessary but I do it anyway.

Just a quick reminder here that when the iridium plugs came out they had a much bigger gap setting and ford were having problems with both early plug failure and coil packs failing especially in the coil pack rather than the coil on plug set up. They struggled for quite some time to resolve the issue but eventually discovered it was due to the plug gapping being to large. There was a point in the early days when plugs were being routinely changed out annually regardless of milage even though they were rated for 100,000 miles or more. Ford then stated a gap of 1.0-1.2 mmm which resolved the issue. The dealer instuction was to set at 1.0mm.

I changed my Iridium plugs at around 40k, but this was because they'd been in since new and were 7 or 8 years old, the OE FoMoCo that came out were clean as a whistle and the gap erosion was only a tho or two, pretty amazing when you think of the hundreds of millions of times they've fired