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From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Advertising leaflet for Lissen Mica Plugs, detailing their benefits and providing maintenance advice.

Identifier  ExFiles\Box 58\2\  Scan185
Date  4th April 1935 guessed
  
THE BRIGHT YOUNG SPARK
The new LISSEN
5/- CHROMIUM PLATED MICA PLUGS

Fit LISSEN MICA PLUGS

THIS EXTREMELY NEAT USEFUL MAINTENANCE CHART FREE WITH EVERY SET OF FOUR 5/- LISSEN MICA PLUGS
LISSEN LIMITED (Registered Offices and Works) WORPLE ROAD, ISLEWORTH MIDDLESEX

Any one of the following reasons justifies the refitting of your car or lorry with Lissen Super Mica Plugs:—
1. Strength and reliability.
2. Detachable, therefore easily cleaned.
3. Perfect heat resisting insulation.
4. Greater mileage.
5. Easy starting under any conditions.
6. No current leakage.
7. No gas leakage.
8. No engine damage likely to occur due to cracked insulators.
These are eight outstanding advantages you obtain by using Lissen Mica Plugs—results which have been proved beyond all question by many thousands of users. Results which are therefore facts and not fancies.

Plugs mean to you MICA Insulation what LISSEN means to your engine

MORE IN A GOOD SPARKING PLUG THAN MEETS THE EYE

Experts say no other method of plug construction is so reliable as the mica principle—upon which LISSEN hold unique advantages. From their radio building section, where it is imperative that good mica is used, they have gained unique knowledge of mica properties, its applications and possibilities. This knowledge has led Lissen to discover and use the very finest mica—the most expensive mica known should be used in plug construction, that is why you find only this mica used in Lissen Plugs. Careful and convincing tests have shown mica to be superior on every count. You gain by using Lissen Mica Plugs. You get more of everything—more mileage—more power and speed—more reliability. You get less wastage—do more good to your car.

HOW TO GET THE BEST FROM YOUR ENGINE

It is imperative that you choose the correct type. Keen drivers may be interested to know a few facts about the most efficient, most economical type of plug for each particular make of car or lorry.
Plugs must be able to withstand heavy duty, heat, oil, and various designs of combustion chambers. This explains why it is impossible to design one type of plug suitable for all internal combustion engines. Running temperatures and oiling systems vary widely between different makes. Conversely it explains why wrongly chosen plugs reduce engine efficiency, cause sluggish running, high petrol consumption and frequent repairs.
Between oil and heat, oil which accounts for heavy carbon deposit if the plug is not properly designed presents the greatest problem but curiously it is through heat—hence carbon—that high resistance and pre-ignition comes about. A truly efficient plug will run sufficiently hot to burn off oil deposit and carbon from the electrodes and mica—but not so hot as to cause pre-ignition.
From such a brief bird's-eye view of plug design, the vital necessity of correctly chosen plugs vividly reveals itself.
The recommendations on the inside of this folder are the results of extensive and careful experiments, of close co-operation with the various manufacturers concerned. Study them with equal care yourself—there is information here you ought to know. Follow them with confidence and know that if you do you are obtaining 100% efficiency from your plugs.
If you do not find your type of car on our list, please send us particulars. Our technical department will willingly place their expert experience at your service.

1. Make certain you obtain the correct type of plug for your engine.
2. The gap of every metric type Lissen Plug is set to .018 in.—this gap is best for all normal engines having magneto ignition. If your car is fitted with coil ignition, increase to .025 in. to obtain best results. Your dealer will effect this simple adjustment when supplying Plugs. As the large majority of American cars have coil ignition all Lissen Sparking Plugs for American cars are set to the correct gap so that no adjustment is necessary.
3. 'Sooting up' of Plugs is caused by (a) using a wrong type of plug; (b) too frequent use of choke; or (c) over rich mixture.
(a) Needs no comment.
(b) Don't keep choke closed longer than necessary.
(c) Wrong size jet in carburettor, usually the Pilot jet. (Have this adjusted by your garage).
4. 'Oiling up' of Plugs is caused by (a) Oil level too high in sump; (b) worn piston or piston rings; or (c) the excessive use of engine as brake when descending hills.
5. Use only good grade petrol and oil.
6. Clean your Plugs as follows :—
DETACHABLE TYPES.
(a) Grip the gland nut in a vice, using a spanner on the body. Never grip the body of the plug in a vice.
(b) Never use emery cloth, sand paper or other abrasives to clean the mica. A petrol soaked rag is all that should be required.
(c) When re-assembling make sure that the gland nut is really tight and also check the gap between points.
(d) When replacing the Plug in engine do not forget the copper-asbestos washer.
MICADEX TYPE (B.S.2).
The insulation in Micadex Plugs being already accessible, it is only necessary for this protecting insulation to be wiped with a petrol soaked rag.
  
  


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