MGA MODIFIED FOR THE NEW MILLENNIUM

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Nov 29, 2013 (4 years and 1 month ago)

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MGA MODIFIED FOR THE NEW MILLENNIUM



SAFETY, FAST AND CONVENIENT


Introduction


My main reason for writing this series of articles
in May 2001
was

to inform all Club
members who own a disc braked MGA of a safety matter. This is involve
d

the design
of the disc brake calliper and the location of the friction pads. On two occasions, one
of the so
-
called “retainer” springs ha
d

fallen out on rough roads. This rather minor
sounding event can lead to a chain of consequences culminating in the

complete loss
of the hydraulically operated brakes. Long before this happens, some “tell
-
tale” signs
become evident, such as an ominous rattling of wire spokes as the friction pads’
retainer pin tries to “abandon the ship”. Moral: investigate any strang
e sounds on an
old MGA
immediately;

your life may depend on it!


Hence, in carrying out this duty of care to my fellow Club members, I describe
d

other
mod
ification
s I ha
d

unleased upon my poor, unsuspecting MGA, over the
first

fifteen
years of ownership.

Naturally, any changes to a car registered as a historic vehicle, as
MGAs are entitled to be, should be kept within the intent and purpose of those
criteria.


To bring an MGA up to modern requirements, for faithful and energetic service in the
new millen
nium
, I ha
d

altered many minor areas of the design and function of the car,
whilst attempting to keep its original essence in tact. For instance, I now use radial
tyres from a safety perspective (who wouldn’t?) but draw the line at changing from
lever sho
ck absorbers. Some changes
at the time of
writing

had

not yet been carried
out but
were

definitely “on the agenda”
. These

future mods

were subsequently

authorised and funded by the “Treasurer of Home Affairs”.

They are now included
with only the protect
ive roll over bar remaining to be completed.


When the
phrase


for the sake of
modernity”
is

applied to an antiquated MGA
,

it
has
to mean more than

just Safety and Fast,
it must
also
become

more Convenient!
So
these

are the
three
headings for the
modifications, below. Most of the changes are of
low cost and independent from each other. Where they

are

related, I have indicated
the connection and order of scheduling the modifications. You may therefore choose
whether or not to go ahead with some o
f the changes. Most dimensions I mention
below are imperial ones, as these cars were built around those measures. It also
reduces the risk of making something tens times too large, as sometimes happens to
those working with metrics! I’m not owning up to

anything here, by the way.


B
efore I list the changes and describe the work in detail, I must seek a disclaimer in
any of the following technical descriptions. Not all cars are exactly alike or in very
good starting condition, so in good faith I will des
cribe the modifications and assume
you will begin with a car and wheels (especially with regard to 48 spoke wires) in at
least good, serviceable condition. Also, a reputable workshop manual should be
consulted and used as the “authority” if you are in any

doubt over a technical issue. I
recommend to members, the Speedpro Series book: “How to Power Tune MGB
-
4
Cylinder Engines for Road & Track” by Peter Burgess, as a useful reference for
making changes to MGAs as well as MGBs.


Finally,
in May 2013,
t
he

ch
anges


have been updated where a better product is
available or in the light of more knowledge and experience in implementing these
modifications.



List of “Safety” Changes


1.

Safety Wires for Disc Brakes


Remove a front wheel to gain access to the rear of
one of the disc brake callipers.
Using approximately four inches of thin malleable galvanised wire, twist it around the
“retainer” spring and the retainer pin behind the disc pads in two loops, one on either
side of the projecting “tongue” of the spring.

This most important modification will
prevent the spring from bouncing out of the back of the brakes on rough roads.
Repeat this modification to the other calliper. The consequence of losing first the
spring and then the retainer pin is that you will lo
se the brake pads next time the
brakes are applied in reverse, then possibly a calliper piston and the hydraulic fluid!


This fixes a significant design flaw in this early type of disc brake on the MGA 1600
and MGA 1600 Mk2. The MGB used 2 very large spli
t pins and 2 retainer springs
per calliper to overcome the problem. The time taken to remove the pads under
racing conditions would have increased, but probably not significantly, a good trade
off for the increased level of safety.



2.

Radial Ply Tyres


Wit
hout doubt the biggest improvement for an MGA in the area of safety and road
grip. The correct tyre size of tyre in radial tyre terminology for the MGA would be a
155 x 15 in an 80 profile (in units mm, inches and height / width profile in %). I have
opt
ed for 165 mm width which means not only is there more width on the road
(equals more grip) but the gearing is made approximately 3 % higher. Unlikely to be
noticeable as a speedo error.


The increased road grip and consequent stronger roadholding can som
etimes cause
deterioration in a vehicle’s handling. In the MGA’s case, an anti roll bar is necessary
to tune out the effects of greater body movement than the manufacturer could have
anticipated when designing the suspension around the typical narrow cros
sply tyres of
the day. This is covered under the topic of “Fast” mods.


Even with radial ply tyres,
the original
lever shock absorbers offer the best
compromise with a damping ratio of approximately 2:1 (between rebound and
bounce) for this type of susp
ension, with its firm springs and limited wheel travel.
More recent designs for sports cars (including the MGB) have been designed with
greater wheel travel, softer springing and probably would benefit from damper ratios
approaching 3:1 for a more comfort
able ride (using modern adjustable telescopic
shock absorbers).



3.

Quartz Halogen Headlights


The brightness of the existing headlights can be improved to a significant degree (by
about 30%) by converting to quartz halogen bulbs. The wattage should not b
e
increased as not only will the generator become overloaded on high beam, but also the
reflector surface will suffer damage from the increased heat dissipation. There is a
slight compromise in the lighting pattern

(round rather than oval)

but the
improve
ment in the high beam more than justifies it
.


T
he bulbs are Lucas “Tripod” Halogen Bulbs BPF/P22d base 12v 65/55w. They are a
direct replacement for the standard tungsten globes, no

changes are
required

and they
are available from Anthony Pearson (www.classicandvintagebulbs.com)
.
Remember
to avoid touching the glass envelope with bare fingers as the skin’s oil will stain the
glass if the bulb is switched on. If you do accidentally touch the surface, a
wipe with
methylated spirits will clean off the oily prints.



4.

72 Spoke Wire Wheels


The original 48 spoke wire wheels are barely adequate for radial tyres. Not only do
radial tyres provide greater grip through the corners, more importantly; they greatly
increase the load under heavy breaking. My recommended wheel would have to be
the 72 spoke 5 x 15 inch wheel used in Morgan’s 4
-
cylinder range. I can confirm that
the 72 spoke “Morgan” wheels, with 165 x 15 tyres, will fit into the bulk head slot
when pl
acing the spare in the boot. Also, these 5 inch wide wheels, with a ¼ inch
increase in offset (from negative 15/8 to 13/8 inches), still clear the body on “full tilt”.
Therefore, the track increase is ½ inches and as a result, the steering has an improve
d
feel on the road at high speed and
slightly
stronger “self
-
centering”. The wheel code
is XW459A
.


The issue of unsprung weight must be kept in mind.

Whilst these wheels are
slightly

heavier with 165 x 15 tyres over the cross
-
ply tyres on the original w
heels, the safety
advances outweigh any penalty in this regard. However, I would not advise going any
wider in
wheels or
tyres
for general road

usage
.



5.

Three Point Safety Belts


The floor mounting points have been chosen for maximum strength and are
located
where the steel frame encircles the wooden floor. The outer fixing is bolted through
the corner plate immediately in front of the front spring hanger. The inner fixing is
bolted through the rear most screw hole by the transmission tunnel after be
ing drilled
out to 12 mm. Note that if choosing a stiff buckle stalk, do not chose the shortest
length without first checking (those in the Klippan series are too short for comfort
unless each seat is as far back as the adjustment allows).


The top mount
can be fixed to the top surface of the inner mudguard with a minor
compromise to occupant safety (collarbones may be broken in a severe accident).
Ideally, the top mount should be high enough to ensure the belt line for mounting
point to shoulder is horiz
ontal. This is only possible if the factory recommended
location is used, as per below. That requires the tonneau panel to be pierced and may
be considered spoiling the finish. Not quite so bad if a full length tonneau cover is
fitted, as the mounting b
olts are covered by fabric. All supplied mounting base plates
must be used as per installation instructions.


In my installation, the top mounting is into the tonneau panel as per the workshop
manual. The body has a “sandwich” reinforcement (outer plate
of similar size and
thickness to match the inner plate supplied with safety belts) for the top mounting and
a quick release on the outer side connection point (otherwise, the belt has to be
unbolted to allow the hood to be raised). The quick release mecha
nism consists of a 5
tonne strength “D” shackle (10 mm thick stainless steel) and a right angle mild steel
bracket (6 mm thick by 50 mm wide by 50 mm high and 40 mm across) to couple to
the floor mounting. Note, a piece of nylon cord is tied around the “D
” shackle bolt to
prevent an embarrassing loss of the shackle bolt when operating the “quick release”
mechanism, probably in the rain with the passenger expressing his or her disapproval
with this additional delay in raising the hood. Estimated to increas
e the time spent by
10%
-

one extra minute in ten minutes, to release and re
-
connect both sides!



6.

Roll over bar


future mod


Tricky design requirements here: must be clear of the hood irons both when stored
under the tonneau panel and upon erection, must

be de
-
mountable if a “body off”
restoration or local repair is required sometime, must not be near driver or passenger
heads and finally, must provided realistic head protection if a roll over occurs. At this
stage, the design requires a single hoop tube

of cold
-
formed seamless carbon steel that
meets CAMS specification, of 45 mm outside diameter.


A clearance height of no more than 250 mm above the tonneau (from the panel
surface centre line to the upper surface of the bar) to clear the erected hood, and

a
width of between 1115 and 1125 mm when formed. All measurements are to the
outer edges of the tube. These will be allow the hood to clear the hoop in erect or in
the folded position. The location on the tonneau panel for entry into the body shell is
directly outboard from the factory recommended location holes for the safety belts.


Support plates are required above and below both the tonneau panel and the inner rear
mudguard panels. The external top plates will be welded into the roll hoop. The
mud
guard and inner tonneau panel plates will be welded into each end of external
support tubes at either side. These structures will give a measure of lateral bracing to
the hoop (through the tonneau panel) and will allow it to be cross
-
bolted to securely
in
to place.


I will incorporate the upper seat belt mountings into the tonneau panel plates, under
the panel surface as per MGA 1600 Mk 2, still ensuring the belts are close to the
horizontal from mounting point to shoulder. More on this item when I have
su
ccessfully fitted the bar.



List of “Fast” Changes


1.

Addition of Anti Roll Bar


The importance of this modification is second only to that of fitting radial tyres. In
fact, it becomes necessary as a means to compensate for the improved grip and the
consequent effect on the car’s suspension under “spirited” cornering. When turning
in
to a sharp corner at high speed, the greater adhesion of the tyres causes an initial
body “lurch” as suddenly weight transfers to the suspension of the outside front
wheel. This downward body movement causes that wheel to lean out with a positive
camber a
ngle, leading to a transitory phase of “roll understeer” as the tyre’s contact
patch on the road is reduced, the drift angle increases and the car consequently starts
to run wide. The effect is a “woolly” feel to the steering for a brief instant. Then, t
he
chassis settles on its suspension, regains its neutral balance and an overall high level
of grip is quickly established. In addition, if road has a bumpy surface and power is
being applied, the lightly loaded inner rear wheel will hop and tramp about d
uring fast
cornering.


A solution to this problem was use of a stiff pair of Andrex friction dampers to the
front suspension in the Le Mans prototype MGA cars of 1955, to improve high speed
stability and reduce transient body roll behaviour. Whilst acceptable on a smooth race
t
rack surface, this change would make the ride on normal roads quite uncomfortable
and thus, was not a popular accessory. There is of course, a “modern” alternative.


The undesirable roll steer and tramp effects can be resisted when the standard MGB
anti

roll bar (9/16 inch diameter) is fitted to the front suspension. Often called a
“stabiliser bar”, this is exactly how it operates when used with the higher grip of
radial tyres. The possibility of mildly increased understeer after the car has settled
in
to a
corner

is barely noticed. The steering response seems to be “crisper” with good
road feel. The rear wheel tramp on bumpy surfaces has virtually gone


without the
need to fit anti
-
tramp bars!


This installation was offered as a “competition” option
on the MGA 1600 and twin
cam models onwards, and I certainly recommended it for all models. The
early
MGA
1500 requires some minor alterations to the front chassis extensions to accommodate
the chassis pivot rubbers and their straps (made from 1/8 inch st
eel plate) or
replacement with the later pattern of chassis extension. All models require
strengthening fillets (made from 5/16 inch steel plate) to be added to the lower
wishbones at the attachment point for the bars’ drop links. The strengthened
wishbo
nes can be purchased.


Whilst meddling with the front end, the inner wishbone bushes should be replaced by
the MGB V8 rubber and steel bushes for improved suspension location and therefore,
improved steering precision, under high cornering loads. To compl
ete the “radial tyre
tuning”, each of the rear leaf spring’s shackle bushes should be changed from rubber
to polyurethane material to reduce lateral movement under hard cornering. This
probably obviates the need to fit that competition (fashion?) accessor
y: the Panhard
Rod!



2.

MGB Water Pump
, Timing Cover and Crankshaft Pulley


The later pump has a greater flow rate and bolts straight in. However, its forward
projection is longer and the pulley wheel must be re aligned with the crankshaft and
generator pul
ley wheels by using the MGB
water pump
pulley wheel. The fan will be
too close to the radiator so ½ inch spacers and longer bolts will be required to re
-
install the radiator further forward.


Unless you can obtain the original style of thermostat with its

“sliding skirt”, you may
wish to fit a copper sleeve to blank off the internal bypass to improve flow through
the radiator. If you fit the sleeve, you must drill a 5 mm hole through the thermostat
flange to allow some flow pass it in the “closed” positio
n, at cold start up. As most
MG owners know, every little bit helps with these cars in our hot summers and
occasional heavy traffic.

Make sure the under bonnet padding is still in place as this
seals the gap between the top of the radiator and the bonnet
. It is important that
all of
the air passing through the front grill into the chamber in front of the radiator can only
pass into the carburettor duct, radiator and heater duct (if fitted).


If over heating is still a problem,
adding

an oil cooler will h
elp
although being placed
in the air stream in front of the radiator reduces the efficiency of the radiator.

Best
left out unless competition work is intended.
If overheating is confined to heavy
traffic conditions on hot days, consider adding a suppleme
ntary
fan;

see the “List of
Convenient Changes” section, under subsection 5: “Electric Fan”.


The timing cover from the MGB has an improved
crankshaft seal and
well
worth
fitting if working on the front of the engine.


The riveted pulley on the front of th
e crankshaft eventually starts to rattle with old
age. When this happens, change to the MGB
vibration damper

type pulley as it
extends the life of the timing chain

and gears
. The only downside is that it
will

now
be
impossible to remove the engine
from

t
he engine bay. The extra half inch of
thickness of the pulley will foul the front of the bonnet opening. The only solution is
to remo
ve it first

if the engine and gearbox have to come out
. This means the starter
motor
must be removed first
(and therefore the oil filter assembly)
so an assistant can
lock the crankshaft with a very large screw dr
iver enmeshed in the ring gear.
The
reverse sequence is necessary for installation
; p
robably why the factory didn’t bother
to fit one in the first pl
ace. However, we are made of sterner stuff
!



3.

MGB Exhaust Manifold


Replace the crack prone and inefficient standard MGA exhaust manifold with the
MGB l
ong
c
entre
b
ranch style of cast iron exhaust manifold
. This unit

is almost as
efficient as a fabricated extractor, without the noise and long term reliability problems
associated with thin walled pipes being next to the exhaust ports
(
and
consequent

to
high
engine compartment
temperatures
)
. This manifold and its twin
branched pipe
can be installed with some judicious fitting (with a large hammer) to just clear the
sump and chassis. Well worth the effort

and looks almost standard
.



4.

K&N Air Filters and Stub Stacks


Probably the best air cleaners available, with a very
effective and proven filtration
system. They look just like the standard pancake style and are just about all that can
be fitted in the space available!


A further efficiency improvement in airflow of about 5% can be obtained by
promoting laminar flow int
o the carburettor throat by adding stub stacks inside the air
filter. As these seem to be hard to find, the following guide can be used if you wish to
make your own.


The preferred material is aluminium plate with a thickness of no more than ¾ inches,
a w
idth of 4 inches and a length of 8 inches. The plate is cut in half to produce two 4
inch squares. The corners are cut off to approximate a circle; exact shape is not
critical.

However, the cutting of the inner diameter hole is. The 1 ½ inch hole must
exactly match the carburettor throat to ensure clean gas flow. The plate is now
annular or ring
-
shaped and its inner and outer edges of one side must be filed or
turned down
with a lathe
to give an elliptical profile
.
The finished product will
resemble h
alf of a donut when sliced right through from one side to the other. Finally,
the holes are drilled to exactly match the mounting holes of the base plates. The front
carburettor base plate and stub stack must be also drilled and filed respectively, to
ac
cept the valve cover oil breather pipe. This needs to be next to the
inner edge of the
filter element so the
degree

of suction from the carburettor throat is minimised.


For a professional installation, the air cleaners should be mounted on studs. This w
ill
allow the outer cover and filter to be removed without disturbing the rest of the
assembly. Therefore, the mounting bolts should be pushed outwards from the
carburettor flanges, base plate slid on, followed by the suitably drilled stub stack,
spacer s
leeves (cut to size), lock washers, nuts, filter installed, outer plate and finally,
outer nuts.



5.

Reset Distributor Mechanical Advance


The distributor in my car is a non standard 25D

type, normally found in the early
MGB motor. Hence, it has a 10 degree distributor advance rather than the standard 12
degree DM2, normally found in the MGA. The 25D is superior in that its rolling
weight mechanism is a later pattern with less friction
and therefore, recommended. I
have modified

distributor’s springs to meet modern fuel requirements. The light
spring may have to be shortened to ensure it is under light tension in static position.
This will ensure the timing does not advance until at l
east 1,000 RPM is reached.
Crankshaft RPM is discussed here to avoid confusion with the distributor speed. The
mechanical advance should commence between 1,000 and 1,500 RPM. The heavy
spring should not operate until at least two thirds of the advance m
ovement is
reached. This will correspond to full advance being reached somewhere between
3,500 and 4,000 RPM.


Assuming the use of 98 octane fuel, t
he static timing should be set at 1
4

degrees
BTDC
, but only if you have a 10 degree advance distributor suc
h as a 25D type and
have confirmed that it can only advance by 10 degrees
.

For standard

MGA “
12
degree


distributors,
set the static timing at
no more than 10 degrees BTDC.


The crankshaft pulley can be marked with chalk at TDC, +1
4

(static)

for

the 25D
d
istributor

(or
+
10 for to DM2)

and +3
4

(maximum) degrees BTDC
. This allows

the
distributor’s settings
to

be
checked with a strobe light to confirm the mechanical
advance operation. The vacuum advance pipe must be disconnected from the
distributor during
this test. Don’t forget to reconnect it afterwards!


C
onduct a road test to c
heck for “pinking” before going too far
. Pinking (pinging)
sounds like someone shaking a half filled tin can of marbles. If detected,
retard
timing
by 2 degrees and test again.

Continue
until it ceases. It should be entirely
absent at full throttle in top gear at 2,000 RPM and above, if you can hear anything
over the usual MG racket!

If your final timing is less than 10 degrees for the 25D or 6
degrees BTDC for the DM2 distri
butor, you have a problem

that needs resolution
.
P
ossibly

the compression ratio is too high for the fuel in your tank.


The spark plug gaps should be set to 28 thou
-
in. I use
NGK BP6ES

and have no
complaints with their performance if cleaned every 3,000 miles.



6.

Unleaded MGB Cylinder Head


The MGB head fitted to my car (an MGA 1600)
has been

converted for unleaded fuel
use. The standard MGB heads, with larger inlet and exhaust valves h
as better gas
flow characteristics (as do the MGA 1600 Mk2 heads
-

identical except “16” is cast
into the rear corner of the head instead of “18”). Unfortunately, the MGB head also
has larger combustion chambers (43 cc compared to 38 cc) than the original

“15”
head. So, although the engine breathes more freely, less use is being made of the fuel
with the lower compression ratio (from 8.3:1 to about 7.7:1). In my case, the cylinder
head ha
d

already been “shaved” by
4
0 thou inches

to restore the
8.3:1 comp
ression
ratio
.


When I convert
ed

to unleaded fuel by
the
fitting
of
hard nickel steel exhaust valve
seat inserts and manganese silicon bronze alloy valve guides, I
took

take the
opportunity to make further modifications and raise the compression ratio. Th
e head
has been

“ported and polished” and valve seats cut to 3 angles for both the inlet and
exhaust. As this
would

bring the
inlet and
exhaust valves very close to the top of the
engine block, a small
“eye
-
brow” shaped
clearance cut (must have at least 4
0 thou
inch at full cam lift)
has been

made at the top of the cylinder bore
s
.


The
recently rebuilt
engine
block
has been over
-
bored by 40 thou

inches
, decked and
fitted with

JP pistons with a 6.5 cc “dish”

in the piston crown
. Consequently, the

engine’s
compression up to about
9.
4
:1

and is

still
suitable for 98 RON (eg. BP’s
“Ultimate” unleaded) petrol.
With a “fast road


cam, t
he expected power gain is
30
%
over the standard 80 BHP for the 1600 cc engine. This will probably
reach

my target
power output, that of the “de
-
tuned” Twin Cam engine (10
2

BHP). The moral here is:
no gain without some pain (and $)!


If money is no object, a

further improvement in maximum BHP of around 6% can be
gained by installing the 1800 cc engine block
. Whilst the high compression 1622 cc
motor produced 90 BHP, the extra 178 cc gave only an extra 5 BHP, so it reasonable
to assume that with similar modifications, the same % increase
s

in maximum power

and torque

would occur
, albeit at lower engine revolu
tions
.

The MGB three bearing
blocks are the easiest, look identical and retain the mechanical tachometer drive.
So
,

along with the flywheel and diaphragm clutch assembly, provided t
he

above
modifications are carried out and that the cylinder head’s combu
stion chamber
volumes are restored to 43 cc
, the maximum power output should approach 108 BHP
.
Although this
increased
peak power
,

when compared with the modified 1600 motor’
output,
appears to be
rather

modest for the effort involved, a really significan
t
improvement is the greater

maximum torque
developed

at a lower engine speed
,

around
20%
more
power from 2,000 to 3,000 RPM. This would improve acceleration
noticeably and make the car easier to drive with the standard 4
-
speed gearbox. There
will howeve
r, be a
modest

increase in the rate of fuel consumption!


Whilst the block change may not appeal to purists (and environmentalists), this
performance enhancement was occasionally seen in the sixties competition era and so
has a degree of
historic
legitimac
y. With the power output approximating that of the
early high compression twin cam 1600 (108 BHP), and with a 3.9:1 axle ratio (always
an option for the MGA

and fitted to my car as it happens
) to compensate for
developing the maximum power at lower
revolutions, an MGA in this form should
come close to matching the twin cam’s on
-
road performance. That in itself, is
something worth replicating.



List of “Convenient” Changes


1.

Single 12 Volt Battery


After many years of putting up with poor starting an
d the occasional expense of
changing one battery after another, with good starting for a while, I become fed up
with this aspect of MGA originality. I decided to fit one 12 volt battery, costing little
more than the purchase price of a single, rather hard

to get 6 volt battery. In changing
from two 6 volt batteries in series connection to one 12 volt battery, I have thereby
doubled the reliability, by halving the number of components that can go wrong!


The battery has been installed on the left hand si
de because this type of car is often
driven without a passenger and any load balancing should take this into account,
especially in competition, where it might actually matter! The other reason is that an
isolation switch can usefully be mounted in the ri
ght hand bay. Existing cabling can
be re
-
used. A removable key type of switch is a good security device as a bonus.
One other advantage is that the petrol pump can be moved into this bay to protect it
from the elements. The normal location looks like a
n after thought by the designers.


Although it is possible to find a small 12 volt battery to fit into the battery bay, as
covered in an excellent article in the Club’s magazine MG Motoring, January 1999
edition (using an Exide AMF 340 or equivalent), I
prefer to use the regular size.
These larger batteries can be “man
-
handled” with a cheap carry strap, at a 45 degree
angle, and slid down into the base of the battery carrier. Also, I recommend a “semi
-
sealed” type due to the exposed position of the carri
er. What ever you decide, I
suggest you read this article first before proceeding with the conversion, as there are
many good suggestions contained in it.


If you wish to proceed with a regular size battery, the following may be helpful. The
left hand si
de carrier bay can easily be modified by using a hack saw to cut through
the vertical rear corner edges of the angle iron base, down to the horizontal surface
(but not through it) and folding the vertical edge out flat. An extension piece of the
same gaug
e of angle iron, formed in a “u” shape to fit around the outside of the new
longer battery, can be pop riveted to the existing structure. Check carefully before
riveting, that the extension is long enough for the new larger 12 volt battery to sit on
the f
lat horizontal surfaces of the bay. Rubber strip should be used to line the base to
protect the battery from road shocks. Special attention must be paid to the battery
clamp, to ensure to battery terminals are cleared, and that the battery is securely
cl
amped. The lead crossing the transmission tunnel to the isolation switch must be
tied to the cross member to prevent it from ever coming into contact with the tail
shaft.



2.

Conversion to Negative Earth Chassis Connection


If intending to install an elect
ronic ignition or a modern FM radio, you will first have
to convert to negative earth. The term “negative earth” refers to the polarity of the
battery that is connected to the chassis. Originally the MGA was connected as
positive earth. To change polari
ty, you must proceed carefully through the following
steps. Assuming a single 12 volt battery is used.


First, disconnect the cables from the battery’ terminal posts.


Second, disconnect the two wires connected to the generator and wrap their ends in
insu
lation tape. Leave the generator physically attached to the motor.


Third, if a radio is fitted, remove it and discard unless it has a polarity switch. If a
switch is fitted, select negative earth and re install.


Fourth, swap over the ignition coil wire
s to the other terminals, to ensure the correct
polarity is maintained in the spark plugs’ high tension circuit. The incorrect polarity
can mean the spark has less energy across the spark plug gap in the combustion
chamber leading to poor high speed perfo
rmance. With the original Lucas coil:
simply connect the wire from the distributor to the coil’s ignition switch terminal
(marked “SW”), and the wire from the ignition switch to the coil’s contact breaker
terminal (marked “CB”). If a new coil has recentl
y been fitted, make sure the ignition
switch wire is now connected to the positive (“+”) terminal and the distributor wire to
the negative (“
-
“) terminal.


Fifth, if an electric fan has been fitted in front of the radiator, swap over the wires.
Don’t forg
et to test the fan when power is re
-
connected, to ensure the fan still pushes
air through the radiator core.


Sixth, check the fuel pump electrical circuit. Capacitor damping of points will be OK,
but the diode damping requires removal of the diode and re
insertion in the opposite
polarity. If a fully electric module is encountered, replacement with a negative
earth
version will be necessary.


S
even
th, re
-
connect the battery, using new connectors for the chassis and supply leads
as the positive and negativ
e terminals as the post sizes are of different diameters.
Connect the supply cable to the positive terminal post via the isolation switch (
ensure
the
switch in the off position). Connect the chassis cable to the negative terminal
post.


Eigh
th, connect
a long (2 metres) insulated wire lead to the positive terminal post of
the battery and take the other end to the disconnected generator and lightly brush the
“Field” terminal (the bare spade connector) with the bared end of wire. A “bluish”
flash should o
ccur with the first wipe. If not, wipe it again several times until it does
this. If successful, the bluish flash indicates that generator has now been re
-
polarised
for negative earth.


If nothing occurs, check all connections, especially that the battery

has been correctly
connected with its negative terminal post to the chassis cable. Then repeat step seven.


Nin
th, remove the long wire from the battery’s positive terminal.


Ten
th, re
-
connect the generator as before, small spade to the Field terminal
and the
heavy lead to generator output terminal post.


Finally, connect up the battery positive and switch on the battery at the isolation
switch and the conversion is complete.


If the two six volt batteries have been retained, merely swap over the link b
etween the
batteries, right hand side battery negative terminal post is to be connected to the left
hand side battery’s positive terminal post. Isolate as required above, by lifting off the
right hand side battery’s supply cable from the battery’s positiv
e terminal post.


Remember to place a warning label on the cable that earths the motor to the chassis,
next to its connection on the bulkhead. The label should say: “Warning: Converted to
Negative Earth Chassis Connection”.



3.

Conversion to Electronic I
gnition


Assuming you select one of the systems that fit into the distributor housing (such as
Pertronix

from Aldon
), the first step will require you to
decide whether you already
have or intend to
convert to negative earth chassis connection.
Note, if
you do not
intend to change to a negative earth chassis connection, y
ou can buy a kit for positive
earth.
Next, isolate the battery during installation

and f
ollow the manufacturer’s
instructions provided with the electronic ignition module with the additi
on of
obtaining some “heatsink” grease (used for mounting semiconductors) before
commencing. Smear this grease under the module’s aluminium base to help transfer
heat away to the distributor mounting plate. Install the module and keep the points
and cond
enser in a sealed plastic bag in the boot in case the module fails.



4.

Stainless Steel Exhaust and Rear Muffler


Money well spent on an occasionally used classic. Make sure the supports are in
good condition and use a 2 inch OD pipe for minimal flow restri
ction. Any larger
will be unnecessary.



5.

Electric Fan


These cars in our climate need a little extra help in coping with the heat load in the
middle of summer in heavy traffic conditions. I have fitted a fan as close as possible
to the front of the radia
tor, operated by a small “pull” switch under the dash. As this
is merely a supplementary fan, I don’t recommend going to the expense of a
thermostatically operated switch.
Just check the polarity of the wiring is correct and
that
fan pushes air into the
radiator when running.


If overheating occurs under arduous driving conditions, consider making the
recommended changes in the “List of Fast Changes” section, under subsection 2:

MGB
Water Pump
, Timing Cover and Crankshaft Pulley
”.



6.

Dash mounted Dipper
Switch


Added as a replacement of the awkward floor unit. The switch is a single pole, 2
-
way
toggle, to allow the power feed to be switched between the low and high beam bulb
filaments. I have mounted it above the turn indicator, in the place reserved fo
r the
optional head light flasher switch.


The existing rubber covered bulge in the lower bulk head panel (to give clearance
from the starter motor) provides a satisfactory footrest once the dipper switch is
removed. The existing arrangement in later MGAs

gives improved support when
driving through corners. Early MGA 1500 may require a fabricated foot rest as the
starter motor is mounted lower and probably clears the front bulk head.



Finally,
in my original article
I acknowledge many fruitful discussion
s with the very
helpful staff and proprietors of MG Sales & Service (Ridleyton) and Octagon Auto
Sales and Service (St Marys)
, sadly no longer in business
. I trust these changes will
leave your MGA as mine is: not only “Safety Fast” but also “Convenient”,

for the
new millennium of the octagon.



Author:

Geoff Goode



Membership No. 564



M.G. Car Club of S.A.