Shiny happy iridium spark plugs

I needed some help to torque up the gear box sprocket nut. I requires such a lot of torque that it is hard to stop the sprocket from rotating without some way to prevent that from happening. I've been lucky in the past by putting the engine in first gear so it when the sprocket rotates it eventually is stopped by a piston on its compression stroke. That's not enough by itself but combined with the rear brake (acting on the gearbox sprocket via the drive chain), it usually does the trick. So it was time for me to put in some spark plugs.   

I carefully cleaned around the spark plug holes in the cylinder head with a long screw driver with a blob of grease on the end. Dirt sticks to grease and then can be hauled up on the end of the screw driver. I also squirted some Redex upper cylinder lubricant into the cylinders, inlet tracts and exhaust ports. This should give the engine an easier time on first start up and help to shift carbon deposits from its earlier life. 

So on to the plugs. The engine was fitted with NGK DPR8EA-9. That code means they have 12mm thread (18mm hex across the flats), an internal resistor, heat grade 8, and a ceramic nose with centre electrode that extends 9mm beyond the threaded section. My factory and Haynes manuals both specify DPR9EA-9 as standard. That is a 'harder' grade that the 8s fitted. Grade is a temperature rating. 9 should mean the ignition will function more reliably at higher temperatures. I've no idea why, truth be told, but the bike was definitely running hot so I figured I might as well fit the recommended 9 grade and sideline the 8s. 

I decided to try NGK iridium plugs. These are coded DPR9EIX9. They are expensive so an indulgence. My excuse is that the bike was suffering from a misfire and I'm trying to make life as easy as possible for the ignition system all around.  

Haynes (left) and  Factory (right) manuals side-by-side
showing DPR9EA-9 specifications

I gapped the plugs at 0.9mm and smeared some copper grease on their threads. It isn't easy getting plugs in and out of these engines because the tunnels in the head are narrow. The fours are tricky enough - the triples more so because the centre cylinder is directly under the frame tube and space severely restricted.

I have one of the original plug spanners from my Daytona 900's tool kit but it is a bit too short to use comfortably with a torque wrench. It has a 12mm internal hex and I have used a oil drain plug key and a socket to work this before. However I found a longer 18mm spark plug box spanner at an autojumble. I think it is from a Suzuki tool kit. In any case, the good thing about it is that it takes a 17mm socket on the top without protruding so far it interfers with the frame. So I could enjoy hearing the satisfying click of my torque wrench at the prescribed 18NM.