En­gine Au­topsy

Tiny but de­pend­able four-pot that lived from 1955 to the mil­len­nium

Practical Classics (UK) - - CONTENTS -

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.

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