The Bearded Lady
THE BEARDED LADY
A Searching Glance at A Delicate Problem
Jack Woods
It is interesting to speculate that if motorcycles had a sex, then the lusty four-stroke would probably be regarded as the male of the species and the more diminutive two-stroke the female. The only flaw in this definition would be that the two-stroke is prone to whisker trouble, which is generally accepted as being a male characteristic! A simple explanation of why this trouble occurs in two-strokes and rarely in fourstrokes is that there are twice as many firing strokes in the two-stroke cycle, which produces a higher working temperature. Furthermore, the fuel and scavenge gases circulate closer to the plug, which suffers drastic temperatre changes when the throttle is operated.
lthough this explanation may well be perfectly / correct, it is certainly an oversimplified one; otherwise spark plug whiskering would have been cured long ago, which it has not. The symptoms of plug whiskering follow a fairly consistent pattern. The motor begins to misfire then usually dies altogether. leaving the novice sitting astride his immobilized ma chine, wondering where to start looking for the trouble, and the more experienced rider busy yanking the spark plug out and breaking a thin metallic whisker across its points with a penknife or even his thumbnail.
his is genuine plug whiskering, or, if you prefer a fancier name, electro-chemical bridging. / Some riders have never met it, and others have been plagued by it. Such whiskers occur at random and cannot be reproduced under controlled test conditions. They are a phenomenon produced by some internal com bustion alchemy peculiar to the two-stroke, the secret of which it has so far kept hidden under its cylinder head. Another form of whiskering known as electrostatic bridg ing is really not whiskering at all, and grounds the plug points via the building up of a miniature stalagmite across them. This is both thicker and of a different com position than the thin metallic whisker which only oc curs on a clean plug. The former usually grows on a dirty one and can occur in both twoand four-stroke motors.
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he explanation given for stalagmite type bridg ing appears reasonable enough at first glance. The trouble is believed to originate from the residue of combustion, in the form of carbon and outside dust, which is sometimes scavenged from the cylinder head by hard driving, being attracted and held onto the plug points by the electrical field in its vicinity. This ex planation is probably correct, although there may be some weakness in the hard driving theory when there are so many instances of really hard, continuous driving in which not even the slightest hint of plug bridging oc curs. In view of this, it would seem much more likely that stalagmite bridging could result from casual motor ing, when the plug runs cooler and has less of a self cleaning effect. But at any rate, this form of bridging is not so mysterious as its metallic counterpart. Indeed, to all intents and purposes it has been eradicated from four-strokes and can be easily controlled in properly maintained two-strokes.
rue whiskering is a much more nebulous prob lem. Attempts to solve its elusive natureareas various as they are unconvincing, and it is not easy to relate some explanations with others. All engine manufacturers seem quite sure it has nothing to do with their engine design. This may very well be true, as metal lic whiskering is haphazard and is not confined to any particular make of motor. A favorite explanation of whiskering is that it originates from the type of oil used. Twenty years ago it was argued that as the two-stroke was very fastidious about its lubrication, the answer to whiskering lay in this direction, possibly through the use of special oils and additives. But today there is a re verse opinion that whiskering is encouraged by the ad ditives in two-stroke oils, which often contain organo metallic compounds likely to separate out during com bustion and become attached to the plug points, It has now been established, after considerable research, that the best base oil for two-strokes is a pure mineral one of paraffinic base, solvent refined and with a narrow boil ing range. This type of oil produces very little carbon deposit and is free from impurities. Provided that the additives to this base oil are chosen with care and are not of the detergent or anti-oxidant type, then the ten dency to whisker will be reduced, but not, alas, com pletely eradicated.
park plug manufacturers naturally have their own answer to the problem and recommend the use of plugs of a heat range and design offering the maximum discouragement to whisker for mation. They argue that whiskering is not fundamentally a plug fault but admit that it is the attraction of the magnetic field existing at the plug points which causes metallic particles to collect on the electrodes. They offer plugs designed to prevent this from happening, some times with silver (and non-magnetic) center electrodes and points, and they pay special attention to heat dissi pation from the points (where a welding effect is most likely) and heat retention inside the nose to deter foul ing. Indeed, one well-known firm (K.L.G.) designed a spe cial anti-whisker plug with a slightly loose earth elec trode so that whiskers cannot obtain a hold. These and other efforts from plug, oil and gasoline firms have all helped to reduce the incidence of whiskering. Any fur ther research into the matter, if warranted, will have the following conclusions to draw on:
1. That a true whisker is mostly composed of lead. 2. That the conditions necessary for its creation are critical and probably a combination of a narrow temperature band and a magnetic field of a cer tain strength reacting on the by-products of com bustion. 3. Probably a factor X is also involved; it could be the pressure inside the cylinder, or anything. 4. A certain cure for one engine will fail on another. 5. The very latest oil additive suspected of causing whiskering is tungsten.
