Thursday, 17 May 2012


Another infill job is required whilst waiting for the return of the cylinder head and ash frame for the boot lid.  Having piped up the brake system, the next logical job has to be the the fuel line and pump.  The original pipes appear to be copper and whilst covered in all manner of crud, they are in excellent condition with undamaged unions.  The SU fuel pump however is in a pretty bad way.  It just looks awful and stinks of stale petrol / old paint and a 12 Volt supply across it met with an unsurprising silence.

Original SU High Capacity (Type LCS) pump - dirty and dead
I can easily replace it by plumbing in a modern Facet pump but there are other considerations:
  • The pipe work and unions would need some surgery with naff looking bits of rubber hose and clips.
  • There is something reassuring about the click - click - click of an SU fuel pump.
  • Depending upon the precise volume, tone and frequency of the "click" a whole range of fuel line faults can be diagnosed.
  • The critical path / weakness, the points can now be replaced with a solid state upgrade kit.  The downside to this is that you will no longer have the satisfaction of hearing the result of a good whack.
  • It is still possible to telephone Burlen, the main UK supplier of parts and have a proper technical conversation with a knowledgeable human being. 
  • I think concours judges should ask for the ignition to be turned on and then deduct a few points for silence or some other inappropriate noise.
Apart from the points under the black plastic cover, the innards and workings of SU fuel pumps have always been a bit mysterious, but with nothing to lose, it only takes around twenty minutes to have it totally dismantled.

Fully dismantled - note 11 brass spherical rollers.  Also note
the amount of very fine black muck on the inlet cover plate
compared to the relatively clean outlet side cover plate

Diaphragm / Bronze rod, brass spherical rollers and return spring
The detailed description of it's operation in the Factory Workshop Manual, coupled with all the bits laid out in front of me eventually unravel the mystery.   The only electrical part of the pump that will be retained is the magnetic coil embedded in the iron core body.  Loosely holding the diaphragm and bronze rod within the central hole in the magnetic core, and momentarily applying 12 volts produces an immediate upward movement and familiar click.

For future reference
A known working magnetic coil measures around 4 ohms
A full service kit and negative earth solid state PCB  are ordered from Burlen.  The end plates and body are painted and all other parts cleaned.   A large amount of compacted fine black muck was removed from the inlet chamber containing the brass gauze filter so this clearly dose a sterling job.

The service kit when it arrives is inspected and I find the bronze rod attached to the diaphragm is around half an inch shorter than the original.  It transpires that this version of pump has a long and short body.  More return postage costs!  Also, the kit contains a new rocker / point assembly which will not be required.

Ready for re-assembly.  Parts on the bottom row are not required

The diaphragm assembly is held central in it's housing by 11 (odd number ?) spherical rollers (thick brass washers) which appear to be unworn.  These are reluctantly replaced by the 5 x figure of eight nylon items supplied in the service kit (see the above picture).   There's probably a good reason for this, but I would be interested to know the thinking behind it.  Also one of the two thin brass discs in the non return valve assembly is replaced with a plastic disc.  It takes a phone call to Burlen to discover which one (its the top one - apparently ?) again - Why

Fitting the five nylon bits around the diaphragm was fiddly but otherwise, re-assembly was fairly straightforward. 
The conversion to solid state was also quite easy and interesting.  An aluminium machined bit (note - the term "bit" is used as a generic term for nondescript items) containing a small magnet is screwed onto the end of the bronze rod in place of the rocker / points assembly. 

Electronic conversion kit fitted.  Aluminium magnet "carrier"
in centre, screwed onto end of bronze rod.

The magnet influences a Hall effect transistor on the PCB which conducts, energising the coil which moves the brass rod and magnet upwards.  Once out of the "influence zone" of the Hall effect, conduction stops, and helped by a big spring, the rod returns to its original position and the whole sequence starts again.  On the pull stroke, fuel is sucked from the tank into a holding chamber and on the return stroke it is sent on it's way to the carburettors.   This is probably an over simplification of the workings, but I think in principle, it's about right.  One thing I have learned, is that the distinct clicking noise is not from the points as I had always imagined, but from the diaphragm centre hitting the body on the pull stroke.

Re-built pump - total cost of parts including electronic conversion
kit and set of new cheese head screws £110.05 plus carriage.
Around the same price of a Facet kit. 
Miscellany - related topics

May 7th, Bank Holiday Monday in the UK saw a few JDC Area 11 members congregate at Croft circuit for a Track Day.  Normally restricted to 88dB maximum (Normal car exhaust level) this was unusually a 105dB day which brought all manner of mad machinery out to play.  My XK140 registered 98dB which I find hard to believe, but was assured that the meter had been calibrated that very morning.
Line up of Jags at Croft.  There was also a full race spec D type
replica, but owner took it home and came back in the 120 OTS
Whilst dry for most of the day, it was bitterly cold.   I did feel somewhat guilty flogging the puddings out of my treasured old 140 fixed head, but any other course would have been pointless.   I also got to ride passenger in a few other exotics, but the highlight was a couple of very quick laps in a C type re-creation (replica would not do this fabulous New Zealand built, tool room copy, justice). I'm never a good passenger but Pilot Geoff Mansfield had me holding on tight with perfect lines and beautifully controlled drifts.  I suppose at his age, he's had an awfully long time to perfect his technique!

Wife Angie's just gone on holiday to Spain, which should mean I'll have a little more to show than a re-built fuel pump in the the next fortnight.

Next Post - Beginning of June