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[jefrs]

The spark gap is set to provide optimum load on the HT coil. If set too close you get a feeble spark, too wide no spark at all. 0.5mm is only 20-thou which seems a trifle small for the C5 with its electronic ignition.



It takes 10kV to jump 1cm of dry air at atmospheric pressure. In the C5 cylinder we will have 8.5 atmosphers of not-dry air, but back of envelope gives 850V to jump 1mm. I found a 1mm gap failed at high revs (missing) but that the olde 25-thou didn't have a fat enough spark, and so settled on NGK's recommended 0.7-0.8mm gap (which they're preset to). I did quite a few plug chops to find one and its setting that would self-clean nicely.

[Scalyback]

Jefrs, is that TR7 negative earth? Postive earth systems flow the other way and that problem does not occur from memory.

[Leon Novello]

Hi jefrs: I have only used Never Seez which has been tested for copper electrolysis without harmful effects. There are some who will tell you that even smearing grease on the threads will cause the same disaster you experienced. I think you were just unlucky with a car that had an inherent faulty plug thread to start with, or a previous ham- fisted owner damaged it by over tightening the plug. The trouble with trying to remove a corroded-in plug with no smear of anti-seize will result in a much bigger problem, tearing out the thread with the plug.

[Rattlebattle]

It seems I misunderstood our host's advice re plug gap; re-reading it it would appear that they are referring to the older pre- EFI bikes. Nevertheless my C5 is running very well at the moment, notwithstanding what plug/cap should be fitted and what the gaps should be.....I'll change the gap to the specified one and see what happens. Re Coppaslip on plug threads I've used it for years and never had a problem on bikes or cars. TR7 s were made during the darkest days of British Leyland; it wouldn't surprise me if a fault existed when it was made. I used to have a TR4; great engine, lousy chassis and rear suspension. I would choose the 3A if I could have any of them.

[JTL]

Hi Paul and Leon... thanks for replies. The ignition set up for my 2003 Bullet 500 is NGK B8ES plug, NGK resistor plug cap, non-resistor HT lead cable, FlameThrower ignition coil (3,2 ohm primary/ 9670 ohm secondary) and points. Points and plug gab is set per manual. Actually the bike runs great. So the reason for me to ask questions is to learn more about especially the electrics on the bike. This way I can hopefully understand (and maybe cure) why most bulbs have a slight and iregular flickering when turned on and my electronic rev counter does not have a steady reading. So I think, can I cure the iregular flow by doing something. And what to do? Has it something to do with Volts, ohm's or whatever the current consists of? Could be a simple thing as using a non-resistor plug cap, but according to Jefrs there has to be a resistor (5 ohm ?) somewhere in line to increase the voltage... I like the idea of "basic". I try to do things simple, basic and easy to understand (+ fix). This is why I ask about "the least numbers and letters"... Jacob

[jefrs]

Scalyback - from memory the TR7s were negative earth.

The one that ejected the plug was an ex-racer with Kent cam and high compression. The trick with a spark plug is to clean the hole's threads and surrounding thoroughly with brush, rag, air jet, vacuum, etc because you don't want any grit. A little grease or oil is ok but not copper.

Because spark plugs have a special compression washer, the correct torque is finger nip-tight plus about a quarter turn.

http://www.globaldenso.com/en/products/ ... index.html

http://www.ngk-sparkplugs.jp/english/techinfo/qa/q18/

And yeah, the previous incumbents probably did gorilla the plugs in and stained the entire area tan with Copper-Eze.



On my +ve earth 1955 Rover 75 the doors were aluminium skin and steel frame, so the phosphor-bronze hinge pins corroded and the door fell off. The opposite polarity caused the copper to erode.

The electrolysis corrosion literally eats away the aluminium making the spark plug hole sloppy, the aluminium pits and looks white and powdery. The problem is not getting a plug out but keeping it in and then it needs a not-Helicoil spark plug insert (cheap part, expensive tool, 10 minute job for garage). The C5 is -ve earth.