spark plugs

[tony]

hi can someone tell me what spark plugs i can put in my 57 dragonfly regards tony

[eddie]

Hi Tony,
             Here in the UK, NGK B7HS plugs perform well. That goes for all post war machines up to and including the Dragonfly.
                                              Regards,
                                                        Eddie.

[tony]

Hi Tony,
             Here in the UK, NGK B7HS plugs perform well. That goes for all post war machines up to and including the Dragonfly.
                                              Regards,
                                                        Eddie.

hi eddie thanks for that only just got douglas shes running but has slight misfire its been standing for many years think clutch is a bit disstorted shudders on pull away but its all original hope to keep it that way. by the way im in sussex near battle

[eddie]

Hi Tony,
              Check out the distributor. Start with the cap - the HT leads are clamped to the top of the cap and it is possible the spark is shorting across to the other spark plug lead. If there is any sign of a track across the surface, scrape it away and then apply a little Vaseline or silicon sealer. There could also be a short to earth on the inside of the cap. Worn bearings in the distributor may also be letting the cam 'float'. These are not so easy to deal with - it has a parallel shaft and skimming it will also leave the timing gear slack. Just about the only way of rectifying this would be to turn up a thin walled sleeve, then Araldite it onto the shaft (use proper Araldite - not the rapid rubbish) - when set, skim the O.D. concentric with the shaft, then bore out the bronze bushes in the body to suit. (Beware, there is a small seal above the top bush).
    Regarding the clutch judder: check that the 6 bronze bushes that fit through the flywheel are free to slide - these have been known to get clogged with dust from the clutch plates - especially if using first generation asbestos free linings. (Later generation asbestos free linings are woven like the original Ferodo material, and don't give that problem). If one or more bushes are dragging, then the plate will lift lopsided.
                                Regards,
                                             Eddie.

[aggettd]

I installed NGK BR7HIX Iridium equivalents to the B7HS recommended above and have found them to be very reliable, making starting easier (1 to 2 kicks from cold or hot, every time in my T35). For me, a definite improvement over the standard plugs, but then "at $20 per plug, there may be some subjectivity to my opinion. YMMV.

[eddie]

Upgrading to modern equivalents is OK on machines with coil ignition, but plugs with an internal resistor are not reccommended for use on engines with magnetos. Evidently, the resistor not only increases the load on the windings but can also affect the point at which the spark occurs. From this, I would assume that the increased load would also aggravate any problems with  the spark tracking to earth - whether being fired by coil ignition or a magneto.

[Stuart Lister]

Hi,  I was told by a magneto specialist, a few years ago, that iridium plugs are ideal for magnetos. The lower voltage required to create a spark more than compensates for the extra resistance. They give the magneto an easier life than the traditional copper ones.

This is just word of mouth stuff of course, and I have no data to prove it one way or the other, but I have been using them for around five years without any problems.

Stuart.

[trevorp]

i think you will find its the air gap that sets the voltage eddie is right resistor plugs use more voltage and iridium last longer as electrode burns less and plug gap stays the same longer therefore uses less voltage