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30/10/2000 |
Terminology
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BBU |
Big Bore Unit |
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SBU |
Small Bore Unit |
NOTE: This information covers transplanting
large-bore engine units into small-bore engined Minis. For further information
for exact differences between pre-A+ and A+ units, see relevant separate
article.
Engine mountings and steady bars.
Engine
mountings are a whizz to fit
as the Mini ones fit straight onto any of the other units. Just remove the
Metro/AA/1300GT ones and swap the mounts over from the Mini unit. If they’re
split, fit new ones, they’re cheap. If using the AA/1300GT unit - it's
advisable to cut off the 'wings' on the front plate that carried the engine
mounts on the radiator end. They get in the way otherwise. As
for engine steadies, fit up-rated bushes to the standard one from block to
master cylinder plate. The one fitted to most late Minis going from the
bottom of the clutch case forwards is a waste of space unless you weld a washer
to the bracket to remove possible slop caused by the elongated bolt hole. Far
better is the one that fits this end and goes rearwards to the subframe leg;
and it’s companion that fits on the left side to the
speedo drive case, likewise trailing to the rear subframe leg. Ultimately the
competition-type top engine steady from thermostat housing to bulkhead cures
all ills in this department.
In all
applications now though, the introduction of the injected cars has thrown a new
spanner in the works. The subframe used in these cars has the engine moved
forward some 3/4" in the subframe. So if you've recently fitted a new
subframe from a very latest spec car - you're going to need to extend all the
engine steady bars!
Cooling.
Some
'doctoring' of the timing cover breather where fitted is necessary to assist
clearing the fan blade. Use a hammer to flatten it where it faces the fan. Use
of a small spacer (available as a separate part) between the fan and pulley
also helps alleviate the clearance problem. Make sure you fit the fan the right
way round - smooth, sculpted-centre side towards the pulley. Use whichever fan
belt suits the water-pump pulley, as many Metros had an oversized pulley to
reduce pump speed (a worthy idea).
Metros use
5/8” heater pipes so conversion to Mini-type cooling makes things easier,
tidier, and more effective. Use the Mini thermostat housing together with a
Cooper S top radiator bracket - the thermostat housing angle is different on
the BBU - and Cooper S or 1275GT top hose. Drill the heater tap take-off
through - the recess is there in Metro heads as are the tapped bolt holes (1/4”
UNF thread) to retain the heater tap. Don’t bother plumbing in the inlet
manifold if the MG Metro heated type is used - colder intake temperature gives
more power! To allow water to circulate prior to the thermostat opening in the
absence of a by-pass hose (Metros use a sandwich plate under the thermostat
housing) drill 6 1/8” holes around the thermostat’s perimeter.
I would
highly recommend fitting a new radiator - the standard Mini one just about
copes with the standard engine. Bigger/more powerful engines generate more
heat; a brand new standard rad will be hard pressed.
Use one of the hi-tech 2-core units; the expense is worth it - cheaper than a
melt down!
Starter
motors.
If using
the flywheel assembly from the SBU out of the car, use the starter too. Going Verto from pre-Verto, count the ring gear teeth. 107
will mean you can use the Mini inertia-type starter, 129 means it’s for a
pre-engaged set up. The Metro pre-engaged starter doesn’t fit a Mini, so a Mini
one is needed. This may prove very expensive, and re-wiring is necessary as the
solenoid is part of the starter. A cheaper way is to fit the relevant ring
gear. If fitting a BBU to a Mini with pre-engaged starter, and intend using the
early flywheel set up it is possible to retain the 107 tooth ring gear. The
engine will spin over quicker and make an odd noise, but it will work. Unfortunately
service life will be much reduced. Change the ring gear - it’s cheaper in the
long run!
Gear linkage
In post
1973 cars where rod-change-type gearboxes are being fitted in place of a
remote-type system, use the entire linkage and gearlever system from the late
Mini if it has to be sourced separately. The older remote fits in a
semi-circular shaped tunnel, the rod-change a square one, so brackets or
spacers are needed depending on what facilities and components you have to
hand. Mini Mania sells a special conversion bracket to simplify matters. The
rod-change’s cotton-reel type rear mounts make this very simple to do. The
fitting’s not too critical PROVIDING the linkage isn’t fitted under tension
fore/aft - it will make the gears jump out. Hang the rods/gearlever housing in
their natural position. Trimming of the tunnel hole may be needed too.
Sometimes it is, sometimes it isn’t. Fit the linkage and try it first.
Useful
part numbers:
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Radiator top hose |
Cooper S |
GRH247 |
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1275GT |
GRH469 |
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Radiator top bracket |
Cooper S |
12G617 |
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1275GT |
12G2453 |
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Rad brkt grommets for above |
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11G227 two needed |
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Rad brkt grommet sleeves for above |
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12A1985 |
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Thermostat housing |
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12G103 |
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Thermostat housing gasket |
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GTG101 |
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Thermostat housing studs |
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CHS2514 three needed |
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Heater tap gasket |
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88G221 |
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Special 2-core rad |
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C-ARA4442 |
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One-piece rad cowl |
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ARP1174 |
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One-piece cowl to radiator bolts |
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SH604031 six needed |
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Fan blade spacer |
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12A312 |
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Fan belt |
Standard |
GCB10813 small water pump pulley - 3.875" dia. |
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Late type |
GCB10838 large water pump pulley - 4.725" dia. |
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Flywheel starter ring gear |
107 tooth |
22G2613 'thin' type as used on race f/wheels |
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12G676 'wide' type (standard manual trans) |
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12G2445 Verto f/wheel with inertia starter |
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129 tooth |
PSF10003 Verto f/wheel with pre-engaged starter or for pre-Verto f/wheel with pre-engaged starter |
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Mini Mania gear linkage bracket conv. |
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