The Beating HEART of Our LBCs

Raymond A. Carbone (First published in the February 2012 PEDC newsletter)

I‘m always amazed at the communication and camaraderie that exists among LBC owners throughout the world. In a recent web response to a call for help on an SU fuel pump problem, a Healey owner in Italy referenced an article by Eric Lembrick in an English MGT club newsletter called T-Type2. Eric‘s article, along with additional research, formed the information- base for this presentation and suggested modification.

The Old Ticker

Over the years I have found the SU pump to be quite reliable and the familiar ticking a comforting sound. However, many of us have experienced a fouled-points failure that had stopped our SU fuel pump in mid-tick. Stranded, it is not unusual for a driver to resort to the elegant hammer for relief from frustration and sticking points. Even with the potential for problems, I and many others still prefer to retain their points-triggered pumps, and some have even installed a second modern pump to dampen any fuel- delivery concerns.

However, can we improve point reliability and pump longevity to the point of eliminating the need for insurance?

The Heart Attack

Since many of us infrequently drive our LBCs and often store our vehicles over the winter, naturally forming oxidation on the tungsten points usually leads to a non- functioning pump. Dressing the points prior to a post-hibernation start is not an uncommon act; however, more often than not we rely upon the oxidation being burned off by the high switching voltage developed by the pump. Although a remedy for oxidized points can be a high-voltage burn-off, high point-switching voltage is the common cause of flashed and burned points and the most common cause of pump failure.

Many of us were under the misconception that because power to the pump normally ranged between 12 and 15 volts, the voltage across the points was also within that range. However, since a coil is used as an active component, several hundred volts are actually generated across the opening points, similar to the way the ignition system coil produces a high voltage across the ignition points. Under these high voltages it is not uncommon for the points to burn, flash, and even weld together during operation.

And the Beat Goes ON

Over the SU pump‘s existence, a number of different diodes have been applied by the manufacturer to help control high-voltage point flash. Although moderately successful, one unintended consequence is the creation of polarity restrictions. Finally, the manufacturer introduced a transistorized triggering mechanism for the SU pump that would eliminate the points and their problems all together, but even these transistorized switching circuits are somewhat sensitive to high voltages and power fluctuations.

More disturbing is the fact that if a transistorized pump fails, there is little to no chance it can be revived to get you home.

Within recent years, electronic components called transient-voltage suppression (TVS) diodes have been designed to protect sensitive electronics from power spikes. This device controls overvoltage by shunting power to ground when it exceeds a specific brake-down threshold.

When applied to our SU pump‘s points, a TVS will shunt off excessive flash voltage while allowing the pump to function within a normal voltage range. The result of applying a TVS to the points of an SU pump is the elimination of high flash voltage with a substantial extension of point/pump life.

TVS Selection

TVS Diode

When selecting an appropriate TVS, a number of operating conditions must be considered. First, the device must be able to pass power through an LBC‘s normal range of electrical operation. Also, we would like the pump to function even when a (generator/alternator) voltage regulator fails and puts out as much as 19 volts. Additionally, since our objective is to prevent high-voltage point flash and burn, voltage must be kept below a level where this condition is created.

TVS Cost

My choice of a P6KE20CA TVS (manufactured by Vishay), at a cost of around $1.50, was made to meet selection objectives. This device will pass power below 21 volts and safely allow the pump to operate under our stipulated conditions. Additionally, the TVS will react at millisecond speeds to impose a clamping (ground-shunt) voltage of 27 volts to eliminate point flash and burn, before automatically resetting for the next points cycle.

Please keep in mind that my TVS component selection was based on the criteria set above, and others may identify additional or alternative conditions from which to select and apply an alternate device. It should not be difficult to identify an appropriate TVS to meet your selection criteria, as there is a large selection of TVSs from which to choose.

Life-sustaining Operation

Installation is rather simple in that a TVS is wired between the ground screw and points fixing- screw on the head of the SU pump. It should be noted that although not sensitive to polarity (positive/negative), a TVS must be directionally oriented toward the ground. Although some manufacturers print an arrow on the TVS pointing toward the ground end, some have writing on the unit that is read from the ground end. Once the TVS is installed and the points are adjusted per the standard SU procedure, you can pre- test and drive with added confidence.

NOTE: Photos for this article are courtesy of the author.

What’s in your boot?

First published in the July 2013 PEDC newsletter

PEDCer RALPH KNUTSEN managed large-system technical support groups for 37 years, so it’s no wonder he is super organized when it comes to preparing his British cars for long drives.

Ralph keeps things he thinks he’ll need for these road trips in two bags: the yellow and red bags go behind the seats, and the rest fits handily in the spare-tire boot. Ralph says that what he takes depends on the destination and distance that he and his wife, Jan, are traveling, but most of the time it’s all in the car. He relates, “Our travels have taken us to some places where services for LBCs are hard to come by, if at all. A break-down could become a homestead.”  

Incidentally, we are happy to know that Ralph and Jan have plenty of room in the boot for a few duffel bags, in place of suitcases. Below are the lists of Ralph’s LBC spare parts and tools, which certainly give new meaning to the motto Be Prepared! 

IN THE
YELLOW BAG: 

 plastic bag 
 leather gloves 
 fuel filter (2) 
 condenser 
 points 
 distributor cap, wire nuts, washers 
 rotor 
 coil 
 spark plug (2) 
 radiator hose repair kit 
 hose repair tape 
 towels (2)—white, red 
 fuse assortment 
 hose clamp assortment 
 electrical connector assortment 
 O-ring assortment 
 vacuum line—8 inches 

IN THE
RED BAG: 

 bungee 
 electrical tape 
 pliers 
 angle pliers 
 needle nose pliers 
 double-end adjustable wrench, large and small 
 adjustable wrench 
 hacksaw 
 Philips screwdriver, bent shaft 
 OE wrench – ½” to 9/16” 
 knife 
 feeler gauge (2) 
 miscellaneous hose clamps, hose, wire, weld tape, zip ties 
 alligator jumpers 
 inspection mirror 
 extension magnet pickup 
 screw/driver handle 
 small screw/driver set 
 small ratchet set 

IN THE JAGUAR TRAVEL KIT: 

 duct tape, electrical tape, radiator self-seal tape 
 JB Weld 
 set of combination wrenches (at least two ½”) 
 set of sockets 
 a screwdriver with interchangeable tips 
 a set of pliers (standard, needle- nose, vise grips, snap-ring) 
 a small puller or two 
 Big freaking hammer (BFH) 
 telescoping magnet & mirror tools 
 wire and alligator clips 
 flashlight 
 voltmeter 
 jumper cables 
 a set of Tyvek coveralls, disposable gloves, leather gloves, umbrella 
 rags 
 degreaser 
 hand cleaner 
 some fluids: brake fluid, oil, bearing grease, Kroil 
 repair manual DVD 
 wiring diagram 
 parts catalog DVD 
 AAA card, JCNA card, cell phone, ignition key, e-mail address of JagLovers 
 spares: V-belt(s), bottom radiator hose, Facet fuel pump, fuses, electrical connectors, and an electrical stripper/crimper, brake light switch, bulbs, air horn, fuel filters, points, rotor, condenser, coil, distributor cap + nuts, spark plugs, flares 

Bringing the PEDC archive to life

Over the next few weeks, look out for a number of ‘NOS’ articles taken from past issues of the club newsletter scheduled to appear on the updated PEDC website .

The articles, mostly written by club members will be guaranteed to make interesting reading, bring back memories and may help with a few technical niggles.

These articles will cover topics such as maintaining an SU fuel pump, an owner’s profile of the Allard J2X, what to carry on a long drive and how to fix your hot-running Healey.

Classic Motorsports spotlight of the PEDC newsletter from 2013