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TECH TALK
- Page 4
More articles below: |
Articles
reproduced with permission from the authors - David DuBois and Ted. |
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Page 1 - MGB & MGC
BATTERIES |
Page 2 - HOW TO LIVE
WITH AN MGC-GT AND STAY SANE. |
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Page 3 - HOW TO LIVE
WITH AN MGC-GT AND STAY SANE. (cont.) |
Page 4 -
Transistorization of SU Fuel Pump |
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Page 5 -
One Grease Nipple - Two
Destinations |
Page 6 -
98 RON FUEL For Your MG |
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Page 7 -
Lucas Info - Wiring, MGA Wiper Motors, Wear in Lucas
Eclipse Drives MGB MK II |
Page 8 -
Lucas Info - Starter motors, Polarisation of Dynamos, MGB
Circlip |
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Page 9 -
Lucas Info - Bearing Replacement, Alternator models for
MG's, |
Page 10 -
Starter fitted to BMC MK II |
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Page 11 -
Fitting Mazda seats to a Mark II MGB Roadster |
Page 12 -
How to Develop the MGC for Everyday Use |
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Transistorization of SU Fuel Pump
(Negative Ground) -
Author - David DuBois |
Several years ago, after my wife
stalled thirteen times while driving across town, I decided to
do something to improve the reliability or the S.U. fuel pump. A
check with a meter showed that when the pump is operating it is
drawing nearly three amps of current through the contacts. This
explains why the contacts burn so quickly and start sticking,
causing the pump and the car to stop running. My solution was to
install a transistor in the circuit so as to reduce the amount
of current through the contacts to approximately 0.4 amps. Since
installing this modification I have put somewhere around 20,000
miles on the car, and at last check the points looked brand new.
Parts required for the modification are:
PNP transistor {Ed. - Radio Shack has a TIP42 (part number
276-2027) rated at 3 amps collector current. This should work
although I have not tried it.} or similar flat epoxy PNP power
transistor (1); 1N4003 diode or similar diode rated at 1 amp,
100V or greater PIV (1); 25 ohm, 1/4 watt resistor (1); 1/8"
shrink sleeving or other insulating material (6"); Solder lugs
(2).
All parts can be obtained from Radio Shack or similar sources
for about $3.00. Once the parts are assembled proceed as
follows:
1. Disassemble, clean and adjust the fuel pump in accordance
with the shop manual. Before reassembling the posts they should
be cleaned and shaped using an ignition file and then polished
using a small, fine sharpening stone or polishing paper. If the
old points are beyond salvage, install new ones.
2. When attaching the stationary point (fig. 1, #1) to the
mounting pedestal, do not put the coil wire (fig 1, #3) under
the mounting screw as you normally would. Instead, put one of
the solder lugs under the screw (fig. 2, #9).
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Fig. 1: This is
what the fuel pump pedestal looks like before conversion. |
3. Enlarge the
hole in the mounting tap of the transistor (fig. 2, #8) I
filed it out to a forked shape and mount it under the
lefthand pedestal holddown screw (fig. 2, #2). Clip off
and discard the center (collector) lead of the transistor.
4. Solder one end of the resistor (fig. 2, #6) to the
lefthand (base) lead of the transistor. Insulate with
shrink tubing. Bend close to the transistor and solder the
other end to the
solder lug attached in step 2 (fig. 2, #9). |
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Fig. 2: And
this is what it should look like after transistorization of
the pump is completed. |
5. Solder the
wire from the coil which you left disconnected in step 2
(fig. 2, #3) and the end of the diode (fig. 2, #7) oppposite
the band to the right hand (emitter) lead of the transistor.
Insulate with shrink tubing.
6. Place the second solder lug under the nut which secures
the pump's "hot" or input terminal (fig. 2, #5) to the
bakelite pedestal. Solder the end of the diode with the band
to the lug.
7. Check to be sure all leads are insulated from each other
and from screws, etc. which could short circuit them, and
that they do not interfere with the operation of the points.
8. Check your work by grounding the body of the pump to any
convenient ground on the car and attaching a wire from the
input terminal (fig. 2, #5) to the positive (+) battery
post. If everything has been done right the pump should
start pumping like mad.
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Fig. 3: For
those of you who understand such things, here's a proper
schematic of the transistorized pump's electrical system. |
It may be
found, when fitting the bakelite cap back onto the pump,
that it will be necessary to grind off the projections on
the inside of the cap in order for it to fit all the way
down onto the pump body. This can be done using a small hand
grinder. Once the cap is on, there is no visible sign of the
modification.
In the unlikely event that the transistor should fail
somewhere down the pike and stop the pump from operating, it
is a simple matter to convert back to the original
configuration and continue on your merry way. Clip the coil
wire (fig. 2, #3) from the righthand (emitter) lead of the
transistor. Remove the resistor lead from the stationary
point (fig. 2, #9), and connect the coil wire to the point.
Remove the diode lead from the input terminal ( fig. 2, #5).
This can all be done by the roadside with a minimum of
tools; a knife or fingernail clipper plus a screwdriver will
do in a pinch. |
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Transistorization of SU Fuel Pump
(Positive Ground) -
Author - David DuBois
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NB. This article
is the same as the Negative Ground only the parts required and
diagrams are different.
Parts required for the modification are: 2017
transistor {Ed. - Radio Shack has a transistor TIP31 (part #276-2017)
rated at 3 amps collector current. I believe this is what the author is
referring to.} or similar flat epoxy NPN power transistor (1); 1N4003
diode or similar diode rated at 1 amp, 100V or greater PIV (1); 25
ohm, 1/4 watt resistor (1); 1/8" shrink sleeving or other insulating
material (6"); Solder lugs (2).
All parts can be obtained from Radio Shack or similar sources for about
$3.00. Once the parts are assembled proceed as follows:
1. Disassemble, clean and adjust the fuel pump in accordance with the
shop manual. Before reassembling the posts they should be cleaned and
shaped using an ignition file and then polished using a small, fine
sharpening stone or polishing paper. If the old points are beyond
salvage, install new ones.
2. When attaching the stationary point (fig. 1, #1) to the mounting
pedestal, do not put the coil wire (fig 1, #3) under the mounting screw
as you normally would. Instead, put one of the solder lugs under the
screw (fig. 2, #9).
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Fig. 1: This is
what the fuel pump pedestal looks like before conversion. |
3. Enlarge the hole in the mounting tap of the transistor (fig. 2, #8)
I filed it out to a forked shape and mount it under the lefthand
pedestal holddown screw (fig. 2, #2). Clip off and discard the center
(collector) lead of the transistor.
4. Solder one end of the resistor (fig. 2, #6) to the lefthand (base)
lead of the transistor. Insulate with shrink tubing. Bend close to the
transistor and solder the other end to the
solder lug attached in step 2 (fig. 2, #9).
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Fig. 2: And
this is what it should look like after transistorization of
the pump is completed.
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5. Solder the wire from the coil which you left disconnected in step 2
(fig. 2, #3) and the end of the diode (fig. 2, #7) with the band on it
to the right hand (emitter) lead of the transistor. Insulate with shrink
tubing.
6. Place the second solder lug under the
nut which secures the pump's "hot" or input terminal (fig. 2, #5) to the
bakelite pedestal. Solder the other end of the diode to the lug.
7. Check to be sure all leads are insulated from each other and from
screws, etc. which could short circuit them, and that they do not
interfere with the operation of the points.
8. Check your work by grounding the body of the pump to any convenient
ground on the car and attaching a wire from the input terminal (fig. 2,
#5) to the negative () battery post. If everything has been done right
the pump should start pumping like mad.
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Fig. 3: Here's a proper
schematic of the transistorized pump's electrical system. |
It may be found, when fitting the bakelite cap back onto the pump, that
it will be necessary to grind off the projections on the inside of the
cap in order for it to fit all the way down onto the pump body. This can
be done using a small hand grinder. Once the cap is on, there is no
visible sign of the modification.
The Sacred Octagon
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Photo
used with permission. |
I have done two pumps like
this and they are running in my 1978 MGB and my 1970 Austin America.
Email me if you have any questions. I couldn't find a 1/4 watt resistor
as they described, so I used a 1/2 watt. Above is my version of
the project. - Ted |
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