Mysteries of the Spark Plug well

[wayne]

Yeah, I know, too much time on my hands..............

Anyway, I have an engine on the bench so why not......here is a shot looking down the spark plug hole. As you can see, the plug sits in a little well and is not directly exposed to the combustion chamber or the apex seals.

The silver metal that can be seen through the hole in the bottom of the copper well is actually an apex seal as it would appear sliding past during operation. I would estimate the thickness of the well at the bottom of the chamfer to still be about 1.5 mm. The firing tip of the standard plug is well away from the apex of the rotor and even with RR's longer plug there is simply no danger of hitting the rotor tip. You'd simply bottom on the floor of the well.

It looks oily only because I flooded the engine with GTX before sealing it up for a thorough external cleaning.

Wayne

[FC Zach]

Very helpful insight that hopefully may deter owners from any paranoia regarding the use of anything other than the standard NGK. It helps decision making when seeing someone else try any new product without fault, good advertising!

[wayne]

Okay, well having said that, I'll explain what I was doing. Depth testing my RR spark plug adaptor. But I just thought that seeing what's down there would be interesting. I've even seen a magazine article where the journo wrote that the original "flush" plug design was to allow the apex seals to sweep past. Not so.

But read on.

The two bright copper lines 180 degrees apart on the bottom of the chamfer are where the twin electrodes of the recommended plug touched when I was gently winding it in by hand. So you can see tolerances are critical. Problem is solved for me by using the recommended extra crush washer. Your engine may be different.

I know one bloke using the adaptor and he reckons he won't be going back to a standard plug. I'm yet to try it.

Wayne