Engine Autopsy
Tiny but dependable four-pot that lived from 1955 to the millennium
A closer look at Fiat’s 600 engine in Sam Glover’s workshop.
Fiat’s mini-car reputation began with the original 500 – the 1936 Topolino with its 569cc four-cylinder engine. Fiat launched this engine’s successor in 1955, with the arrival of the innovative 600. The water-cooled 633cc overhead valve unit had three main bearings rather than the Topolino’s two and induction moved to the other side of the cylinderhead, but the appearance and layout was similar.
It was oversquare and revvy. High-quality and generously-sized Vandervell crankshaft bearings allowed it to survive hard driving. With a block just 14in in length, it was perfect for its rear-mounted position in the 600.
The engine – or its block, at least – went on to be adapted and enlarged to power the 850, then the 127, the Panda, the Uno, the Cinquecento and, finally, the Seicento of 1997.
[A] CRANK PULLEY The 600 has an unconventional way of cooling itself. The crank pulley drives the dynamo via a V-belt. This drives a second V-belt to the water pump, which is a separate casting mounted to one side. It also turns a fan, cooling a radiator sitting in the offside of the engine bay.
[B] CYLINDERHEAD The head has an unusual but pleasingly compact path for the gas-flow. A single carburettor is mounted on top of the head. It sends mixture down into the inlet ports and out through the exhaust ports (top, with a few missing studs). The rocker cover has a linkage that connects the throttle cable to the carburettor.
[C] COVERS The timing cover is the larger of the two aluminium castings. It has an oil seal to allow the nose of the crankshaft to protrude through it and engage with the pulley. The smaller cover – the ring-shaped object with wing-like projections – fixes to the rear of the block and forms the crankshaft rear oil-seal around the large diameter, just aft of the crank’s rear main bearing.
[D] ENGINE BLOCK The small cast-iron block is conventional enough, with apertures for the oil filter housing (just visible on the side, upper right), the dipstick (lower right) and the distributor (the larger extension, extreme right, mirrored in the cylinderhead casting). The oil pressure relief valve fixes into the nearside (extreme lower right).
[E] OIL FILTER This alloy casting fixes to the side of the block with three bolts. The filter canister attaches to the base of it and contains a replaceable paper element – quite a bonus in an economy car at a time when a gauze strainer was generally considered sufficient. Earlier versions had a centrifugal filter built into the crank pulley instead.
[F] OIL PUMP AND SUMP The oil pump fixes to the underside of the front of the block. It’s turned by the small shaft just above it, which receives drive from the scroll gear on the camshaft (see opposite) and also turns the distributor situated directly above it. The foot of the pump housing dips down into the pressed steel sump, which makes do with just a single baffle.
[g] VALVES The tiny but sturdy valves have no stem oil seals; an occasional puff of blue smoke didn’t worry Fiat drivers in 1955. They're held up by conventional single springs trapped under a cap and secured with collets.
[h] ROCKER SHAFT The shaft mounts on four posts on top of the head. The pushrods emerge from the nearside of the engine, threading between the exhaust ports. They push up on the rockers to open the valves, which are in a row on the other side of the shaft. [i] PUSHRODS AND FOLLOWERS The long pushrods reach down to the low-mounted camshaft and followers. When installing the assembly, you have to invert the block, insert the followers from below and then fit the camshaft to stop them dropping out again when you turn it the right way up.
[j] Timing GEARS The smaller timing wheel fits over the nose of the crank, located by a keyway. The larger wheel bolts to the front of the camshaft. The chain is duplex and compact – the wheels are so close together when mounted that their teeth almost touch.
[K] CAMSHAFT Next to the nose of the camshaft is a circular bronze bush that fits over that large journal next to the scroll gear. A hole in the side of this bush lines up with a hole in the block. Through it fits a threaded pin with an eccentric end, which can be turned to move the bush in or out, adjusting the camshaft’s end-float as it bears on the side of the scroll gear. The two smaller camshaft journals run in bushes, too, rather than directly in the block.
[L] RODS AND PISTONS The pistons are only 60mm in diameter, though this rose to 62mm for the 767cc engine in the 600D, and then to 65mm for the 850 and the longer-stroke 903cc engine used in Pandas, Unos and others. A few rarities such as the Autobianchi Abarth A112 pushed it as far as 67.2mm, making 1050cc with a 74mm stroke.
[M] CRANKSHAFT The centre main bearing also carries two pairs of thrust washers (centre right). All journals are generously wide. The strength of the bottom-end contributed directly to the engine’s long and varied lifespan.
[N] BEARING CAPS The big end caps are wide, but tiny in diameter. The slots in each side of the larger centre main cap hold the thrust washers. The shells are seen upper right.