General description
The Mini engine is a four-cylinder, water-cooled, overhead valve type of 848, 970, 997, 998, 1071, or 1275 cc displacement, depending on model and year of manufacture. The engine is bolted to the transmission assembly, which also forms the engine sump, and the complete power unit is supported, via rubber mountings, in the front subframe.
The cast iron cylinder head contains two valves per cylinder, mounted vertically and running in pressed-in valve guides. The valves are operated by rocker arms and pushrods via tubular cam followers from the camshaft located in the left-hand side of the cylinder block.
The inlet and exhaust manifolds are attached to the left-hand side of the cylinder head and are linked to the valves via five inlet and exhaust ports of siamese configuration.
The pistons are of anodised aluminium alloy with either split or solid skirts depending on the model. Three compression rings and a slotted oil control ring are fitted to all types. The gudgeon pin is retained in the small-end of the connecting rod by a pinch-bolt on 848 cc models, by circlips on 997 cc and 998 cc engines and by an interference fit on 970 cc, 1071 cc and 1275 cc Cooper S engines. At the other end of the connecting rod, renewable white metal, leadindium, or lead-tin big-end shell bearings are fitted.
At the front of the engine a single row chain drives the camshaft via the camshaft and crankshaft sprockets. On 1275 cc Cooper S models a duplex timing chain is fitted. On all models the chain is tensioned by two rubber rings on either side of the camshaft sprocket teeth. The camshaft is supported by three bearings, two being bored directly in the cylinder block while a white metal bearing (which is renewable) is fitted at the timing chain end. On the later 998 cc engines and all the Cooper and Cooper S units three steel-backed white metal camshaft bearings are fitted.
The statically and dynamically balanced forged steel crankshaft is supported by three renewable shell type main bearings. Crankshaft endfloat is controlled by four semi-circular thrust washers located in pairs on either side of the centre main bearing.
The water pump and fan are driven together with the dynamo by a V-belt from the crankshaft pulley.
Both the distributor and oil pump are driven off the camshaft, the distributor via skew gears on the right-hand side, and the oil pump via a splined coupling from the rear.
Major operations possible with engine in car
The following operations can be carried out when the engine is in the car:
(a) Removal and refitting of the cylinder head and valve gear
(b) Removal and refitting of the timing chain and sprockets
(c) Removal and refitting of the clutch and flywheel
(d) Removal and refitting of the engine mountings
Major operations requiring engine removal
The following operations can only be carried out after removing the engine from the car:
(a) Removal and refitting of the main bearings
(b) Removal and refitting of the big-end bearings
(c) Removal and refitting of the piston/connecting rod assemblies
(d) Removal and refitting of the crankshaft
(e) Removal and refitting of the camshaft
(f) Removal and refitting of the oil pump
Methods of engine removal
There are two methods of engine removal. The engine can be removed from under the car, complete with subframe, or the engine can be lifted out through the bonnet aperture.
In either instance the engine is removed complete with the transmission, and also the radiator.
It is easier to lift the engine/transmission assembly out of the engine compartment with the aid of a suitable hoist than to separate the subframe from the body, and lift the body up, using the rear wheels as a pivot. This is especially so with hydrolastic models. The subframe comprises the frame itself, the wheels, driveshafts, hubs, and suspension, complete except for shock absorbers.
In either case, it is necessary to raise and support the front of the car so that it can be worked on from underneath.