MG Enthusiast – July 2019

Tuning Guide

62 MGE AUGUST 2019 http://www.mgenthusiast.com

them and lengthening the stroke.
The most common conversion,
made famous by A-series tuner
and author David Vizard, was
a 1430cc conversion to
a Mini 1275GT engine,
achieved by enlarging
bores to 73.65mm and
using topped-and-
tailed Triumph 1300
pistons. The stroke
of the standard crank
was lengthened to

ABOVE: These are 73.5mm diameter
pistons from Omega. They use special
18mm pins and require the use of
low-friction, narrow piston rings.

ABOVE: These shorter pistons are
low-weight and some have a short
compression height, depending upon
engine specification and capacity.

ABOVE: Here you can see the difference between the standard and short piston

height. Shorter pistons are used when the ‘stroked’ 86mm crank (1460cc) is

fitted. Standard height pistons are used with standard-stroke cranks.

ABOVE: The third upgraded component, or set of components in

this case, is the con rods. These are, again, manufactured by Arrow.

LEFT: The rods are fitted with small-end bushes as the gudgeon

pins are fully floating. This means that the pistons do not have to

be machine-pressed on and off; useful if you do decide to build at

home. Each piston pin is secured with a pair of wire circlips.

84.3mm. To achieve the extra-long

throw, the larger 1300 crank’s big

end bearing journals were offset-

ground to (the smaller) Cooper S

size and Cooper S or MG Midget

rods used. It made a good road

engine, the long stroke providing

excellent torque, but it was not the

best engine to be taken to high revs.

Later versions of this used a

73.5mm bore and the resulting

capacity, with the same lengthened

stroke, was 1425cc. A-series engines

could be stretched considerably

LEFT: Building an engine with such

expensive components needs to be

carried out with the utmost care!