BBU - Big Bore Unit
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 swop 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 subframes used in these cars have 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!
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!
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!
NOTE; It is entirely feasible to use the pre-Verto flywheel and clutch assembly with the later pre-engaged (integral solenoid) type starter motor. The best way to accomplish satisfactory fitment is to fit the narrow ring gear of either the Verto flywheel (part no. PSF10003, 129 teeth). However, the standard pre-Verto ring gears (107 teeth) will also work OK with the pre-engaged starter, albeit somewhat noisily that will shorten ring gear and starter bendix life. Where the standard, wide ring gear (0.50-in wide) is fitted, a 0.125-in spacer MUST be fitted between the starter and the transfer gear case to prevent the starter bendix from being permanently engaged. Washers to the value of 0.125-in will be Ok for a short period, a proper, full spacer plate duplicating the starter mounting plate is necessary to ensure long life of the starter. Failure to do this will cause extensive damage to ring gear and starter at the least. The thin ring gear (0.345-in wide, part no.12G2613) such as used on the ultra light and steel lightweight flywheels is used, no spacers are required.
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:
|Radiator top hose||Cooper S||GRH247|
|Radiator top bracket||Cooper S||12G617|
|Rad brkt grommets for above||11G227||two needed|
|Rad brkt grommet sleeves for above||12A1985|
|Thermostat housing gasket||GTG101|
|Thermostat housing studs||CHS2514||three needed|
|Heater tap gasket||88G221|
|Special 2-core radiator||C-ARA4442|
|One-piece radiator cowl||ARP1174|
|One-piece cowl to radiator bolts||SH604031||six needed|
|Fan blade spacer||12A312|
|Fan belt||Standard||GCB10813||small water pump pulley (3.875"dia.)|
|Late type||GCB10838||large water pump pulley (4.725" dia.)|
|Flywheel starter ring gear||107 tooth||22G2613||'thin' type as used on race f/wheels|
|12G676||'wide' type (standard manual trans)|
|12G2445||Verto f/wheel with inertia starter|
|129 tooth||PSF10003||Verto f/wheel with pre-engaged starter or pre-Verto f/wheel with pre-engaged starter.|
|Mini Mania gear linkage bracket conv.||22G2026MM|