Helpful Hints on Distributors, Brake Rotors, and adding Electrical Accessories are presented from the Archives of the Pacific Tiger Club's Newsletter. These particular articles were written by Jim Leach.


Joseph Lucas usually gets blamed, but you would be surprised at the damage to Lucas distributors caused by careless and inept mechanics. I have rebuilt or replaced over a dozen units that have failed because of ham-handed tune-up-artists making the same mistake: they all have dropped one or more of the small screws that attach the ignition points and condenser, into the space below the breaker plate...and then sent the car back down the road without removing them. The screws interfere with the mechanical advance counterweights and jam between the weights and the inside of the case. This usually causes at least one of three things to happen: the driving dog on the bottom of the shaft shears off: the mate to the dog on the oil pump shears off: the distributor's case explodes. I disassemble these "trophies" and keep the parts to restore surviving distributors. I once gave my Minx a tune-up that was good for less than a day: I made an error not to be repeated. It was a very cold winter morning and I was in a hurry, so I used a can of aerosol carburetor cleaner or brake cleaner to blast away some of the grease and dirt off of the breaker plate. I oiled the cam as usual, dwelled the points, changed the spark plugs: everything looked normal and the car ran well. The following morning, after 20 minutes running time, the engine barely ran and then stalled. A complete distributor tear-down and inspection revealed the (previously shiny) cam was rusty brown, the case was full of muck and the drain holes were blocked. The solvent had pooled in the bottom of the casting and it vaporized when I ran the engine and it heated. The vapor rinsed the lubrication off of the cam and overnight it rusted: the roughened cam "attacked" the rubbing block on the new ignition points and the gap closed. On Series Rootes cars there were two versions of Lucas DM 2 distributors (early and late) and they were equipped with two different model vacuum advance units. The early version has a 3/4" hexagonal tube and nut projecting from the body, and a threaded portion at the outlet to accommodate the fitting on the steel vacuum tube running to the carburetor. Beginning about 1960, the hexagonal tube and nut were eliminated, and the threaded portion remained. They were available under a variety of part numbers (superseded many times) and had slightly different operating characteristics from each other. (The original version used a different breaker plate top-half, and was connected to the vacuum unit from below the plate by a Mechanno-set style link. The design was short-lived and was replaced by the spring style, about 1957. This model distributor may be updated by replacing the breaker plate top half and the vacuum unit.) There may be many British cars in service that have failing vacuum advance units. I was recently surprised to discover seven of the DM 2 type vacuum advance units in my storage (both types) have failed while sitting on the shelf. I last tested them about two years ago and they were functional. I suspect they suffer from old age and the natural rubber (?) diaphragms have dried out and lost their flexibility and their seal. The later model vacuum advance units as fitted on 25 D series Lucas distributors introduced in 1963 will interchange with the earlier types; however, the threaded portion was eliminated and a nipple is provided to accommodate a rubber fitting or hose. To run efficiently, an engine requires a certain amount of ignition advance: often in excess of 30 degrees. The mechanical advance unit located under the breaker plate and the vacuum advance unit described above work together to advance the ignition timing depending on an engine's speed and its load. At speed, a defective vacuum advance unit will reduce the (necessary) total ignition advance and may be a cause of overheating: retarded ignition advance will also reduce engine performance and mileage. A leaking vacuum diaphragm provides extra air to an engine and may contribute to poor idling. At every tune-up, be sure to check the vacuum advance mechanism and ensure it is working correctly. ...see you in my mirrors!


SUNBEAM BRAKE ROTOR WARNING by Jim Leach (reprinted from Pacific Tiger Club Newsletter, Nov. 1996 Over the last few months I have heard of a number of failures of Sunbeam Tiger front suspension components. Gary and Carol Christensen collapsed their second front hub in an autocross last year and that prompted many of us to have our hubs crack-tested (magnafluxed). Doug Yip discovered two cracked hubs on his car, and two of his spares were cracked as well. >From the Internet, Dick Sanders reports a number of failures of lower 'A' arm fulcrum pins. The front suspension on my Sunbeam Tiger was sagging and had several cracks developing: all have been expertly repaired by Larry Atkisson. In the process of installing new bearing races in my new aluminum front hubs (from Bud Bohrer) I have discovered fractures in both of my original front rotors. The cracks begin from the four mounting bolt holes and travel inward to the large center hole. The only way to detect these cracks is to remove the rotors from the hubs, as these cracks are concealed under the boltheads. Actually, I wasn't too concerned about these cracks because the hub center supports the rotor and the web of material there is less than a quarter of an inch. Then I discovered a NINTH crack. This one begins at one of the same bolt holes and travels outward toward the brake pad surface. In other words, this rotor has the equivalent of a four and a half inch crack across it's equator (the center hole is about two and a half inches of this). It is very possible these fractures have been there since long before I bought the car. On the other hand, I put five seasons of Vintage racing on them with full metallic pads, and I assure you they have been very hot. If you are racing and using original solid front rotors I recommend you check them now. Street driven cars are probably safe, but should be carefully inspected the next time you replace the pads and repack the wheel bearings. ...see you in my mirrors!


How to Keep the Smoke Inside the Wires or, Why do the English Drink Warm Beer?

...(they all have Lucas refrigerators!!!) by Jim Leach

The first time I heard the Lucas puns I chuckled too, but most of the stories of the "Prince of Darkness" are unwarranted. I have worked on dozens of Lucas equipped cars and you might be surprised at the real reason for most of the electrical system problems. The following is neither typical nor exaggerated; it is a classic and true example of what I have found trying to keep the electrical "circulatory systems" of English cars healthy. In Portland, Oregon I bought a 1961 Hillman Husky whose prior owner was a member of the J.C. Whitney "add-a-useless-device-of-the-month-club". Stuffed between the grill and the radiator was a klaxon (submarine diving alarm). Under the dashboard a battery inverter (to change + ground to - ground) and an intricate alarm system added a couple of dozen wires running in all directions, and a fancy stereo with amplifier and graphic equalizer added to the birdsnest of wiring. Two sets of speaker wires from prior installations remained, as did some of their power wires. Wiring had been routed for fog or driving lights and all of this was crammed up under the dashboard, and every device was wired directly to the ignition switch. Absolutely nothing electrical in the car worked. To restore the electrical system I removed all of the junk that had been added, including three pairs of sharp-edged metal brackets (better suited for fence repair) that in years past may have mounted 8-track tape players, and I simply returned the original wiring to stock. The small contacts in the ignition switch had been severely overloaded and destroyed when they were forced to carry many times the current for which they were designed. The electrical problems were caused by the parasitic additions to the original wiring harness, or by the "golden tooled" person that incorrectly installed them, and are not representative of "lousy-Lucas-electrics"...but Lucas traditionally gets the blame. I replaced the ignition switch and everything works. The Husky wiring harness was in fairly good condition under the dashboard. My Tiger, on the other hand...every other wire was brown...the workmanship of another genius.


(Devices independent of the ignition switch) Create new fused circuits originating from the battery side of the starter solenoid. This is a convenient junction and is electrically equivalent to the "hot" battery terminal itself. (Note: All devices so installed, are isolated from the factory wiring harness and will not register on the ammeter) Example: Electric radiator cooling fan An Electric Fan should be able to continue to cool the radiator with the engine stopped (ignition key removed). It should have its own thermostatically controlled on/off switch. Example: 12 volt power outlet (same as a lighter socket) If you want to be able to run your 12 volt coffee pot or an air compressor at the autocross track, you need to have a power outlet capable of handling a large amount of current. The accessory terminal contacts on the ignition key were not meant to handle the current it takes to brew coffee. This is not an example of "lousy-Lucas-electrics" but of design parameters. By the way, I have a 12 volt RV coffee pot I use in my Tiger and Minx on cold foggy mornings at the race track!


(Devices switched on and off by the ignition switch) Example: Am-Fm Stereo receiver It is usually desirable to connect a radio so it automatically shuts off when the ignition key is removed from the switch: this insures the device cannot drain the battery after you leave the car. On most Lucas ignition switches, the accessory contact is terminal #4. Always check the wiring diagram before adding any fused accessories. Example: 12 volt power outlet (same as a lighter socket) If you want to use a radar/lidar detector or other device that draws minimal current, you may want to install a switched power outlet. As above, the power outlet and device connected to it will not be accidentally left 'on' when you leave the car. (Note: All devices so installed become part of the factory wiring harness and will register on the ammeter)


The starter motor on most cars is relay-switched. It is more practical to use a small wire connected to the ignition switch to energize the starter solenoid (a relay), and have it handle the large current requirements of the starter motor. The same theory applies to some automotive accessories such as high power or multiple driving lights. Depending on the accessory, the relay may be connected either directly to the ignition switch as a switched accessory or to a dashboard or console mounted switch, or to both. This technique has advantages over direct wiring of accessories: the control wires from the switch to the relay can be small gauge; their length is not a concern; and the switch handles only the current required to energize the relay. The large capacity wiring that actually handles the load can be routed directly to the accessory, and can be kept shorter resulting in less resistance and/or loss. Keep in mind, Lucas charging systems were designed to maintain the charge of the battery with the standard ancillaries operating (heater blower motor, windshield wiper motor, etc.) and there is little surplus current generated to cover the requirements of rally lights, sub-woofer blaster stereo systems and the like. In this case, the charging system is something like a garden hose. One hose can water a pretty good sized garden, but if you connected this hose to a sprinkler system at a golf course, there wouldn't be enough water to do the job. The charging system could operate perfectly and in a short time you could still end up with a very low battery.


A simple comparison The Voltmeter: A voltmeter is a device that samples the pressure of electrical potential, present in a circuit, at a given instant. The pressure is called voltage or electro-motive-force. A voltmeter has a high impedance or internal resistance and is always wired in parallel, in relation to the components of a circuit. The usage of a voltmeter is similar to sampling the air pressure in a tire with a pressure gauge. It is accomplished from outside the circuit (or tire!). The electric water temperature gauge and fuel gauge are both examples of voltmeters. The Ammeter: An ammeter is a device that registers the "current affairs" occurring within a circuit: it measures the rate of electron current flow, at a given instant. It samples the number of electrons, in coulombs per second flowing through it. The rate of flow is expressed in units called amperes. One coulomb is equivalent to about 6 billion-billion electrons-per-second past a fixed point in a conductor. (6.25 X 1018 electrons per second). This is a measurement of quantity over time. An ammeter adds no significant resistance to a circuit and it consumes no energy: it is always wired in series with the components of a circuit. ...see you in my mirrors!


  + The Roots of Rootes
  + History of the Tiger
  + Tiger Model Overview
  + Tiger Production
  + People & Pioneers
  + Workshop Manual
  + Factory Race Equipment
  + Literature: Books
  + Articles & Videos
  + Advertising

  + See Rootes Resources

  + History of the Tiger
  + Sunbeam Tiger 2005
  + Early Race History
  + Ken Miles, an appreciation
  + The "Beastie" explained
  + The Playboy Pink Tiger
  + Casting a Light on Lucas
  + LeMans at Goodwood 2002
  + Monterey Historics 2003
  + My Life With Cars

  + See Articles & Humor

  + High Perf. Exhaust
  + Tiger Dash Restoration
  + 350 Lunati Tiger
  + Installing a T5
  + Sound Advice
  + Installing New Carpet
  + The Ackerman Angle
  + "Cool It Buddy"
  + 3 Point Belts
  + Tiger Rotisserie Plans

  + Tiger E-Mail List Archives

  + See Technical Tips

  + Tiger Club Information
  + Events Calendar
  + Service Directory
  + Owner's Gallery
  + Buyer's Guides
  + Contributing Editors
  + Team Tiger Updates
  + Photo Gallery

  + See Online Resources

Anyone who would like to contribute to this effort should contact us at Editor E-Mail. Thank you.

Volunteers wishing to join our team are welcome. Take a look at our Contributing Editors
This site has been designed to pool the collective resources of the many great regional and national Sunbeam Tiger clubs. Membership to the these clubs is strongly recommended. Use our Clubs and Organizations Directory to find the organization nearest you and get involved.