Z650 ENGINE STRIP

It may look like a smaller ver­sion of ear­lier Z fours, but look in­side and it’s very dif­fer­ent

Classic Bike (UK) - - CONTENTS -

Kawasaki’s rather ex­cel­lent in­line four spread over the work­shop floor in lots of easy-to-lose parts

Kawasaki took the dou­ble-over­head-cam in­line four­cylin­der engine from the realm of Grand Prix rac­ing and put it within reach of the street rider. The break­through 900cc Z1 four of 1973 was a 130mph-plus sen­sa­tion, but there was a draw­back – the King of Mo­tor­cy­cles and its Z900 and Z1000 vari­ants were bulky ma­chines with im­pre­cise han­dling.

Gy­oichi ‘Ben’ Ina­mura, who had over­seen the de­sign of the Z1 engine, re­fined the dohc four con­cept to cre­ate a more com­pact unit that was cheaper to make. The re­sult was the 652cc Z650 (or KZ650 in the US and other mar­kets) launched in late 1976 to of­fer rid­ers an ag­ile and ver­sa­tile four with sharp ac­cel­er­a­tion and a near-120mph max­i­mum. Kawasaki’s claim that its 650 pos­sessed 750 per­for­mance was backed up when fac­tory-pre­pared KZ650S set 750cc-class en­durance records at Day­tona in 1977, in­clud­ing 100 miles at 130mph. More proof of re­li­a­bil­ity came from Amer­i­can Rich Wil­let’s 9550-mile jour­ney to break the record for rid­ing around the coasts of Aus­tralia.

Al­though the 652cc engine looks like a smaller ver­sion of the ear­lier Z fours ex­ter­nally, it dif­fers con­sid­er­ably in­side. In­stead of a built-up crank­shaft with roller bear­ings, the smaller engine has a one-piece shaft with plain shell main and big-end bear­ings. Pri­mary drive is also dif­fer­ent with an in­verted-tooth Hy-vo chain to an in­ter­me­di­ate shaft, rather than di­rect gears. Few changes to the de­sign were made dur­ing a pro­duc­tion run that lasted un­til 1983. The most sig­nif­i­cant were a self-ad­just­ing cam chain ten­sioner in 1979, the in­tro­duc­tion of a qui­eter Hy-vo cam chain in 1980, CDI ig­ni­tion in 1981 and four-ring pis­tons in 1983.

The engine here dates from 1979. The crank­case has five cast-in hous­ings for the main bear­ing shells and four more for gear­box

shaft bear­ings, all on the axis of the hor­i­zon­tal split. A cast-al­loy oil col­lec­tion sump is screwed to the un­der­side of the crank­case.

The crank­shaft’s crankpins are dis­posed at 180° in­ter­vals; the outer two are at top dead cen­tre when the in­ner two are at bot­tom dead cen­tre. The in­te­gral sprocket for the cam chain is lo­cated cen­trally, with teeth for the drive out­put chain cut in the crank me­tal to the left of it.

A keyed ta­per at the left-side end of the shaft car­ries the al­ter­na­tor’s mag­netic ro­tor, which sur­rounds a 12-coil sta­tor. The other end of the shaft drives the ig­ni­tion points unit, which has four con­tact break­ers and an auto-ad­vanc­ing mech­a­nism.

The con­rods’ split big-ends are held to­gether by bolts with heads shaped to lock against the rods as the nuts are tight­ened. The gud­geon pins bear di­rectly on the rod me­tal in the small-ends, sup­port­ing con­ven­tional three-ring pis­tons that have their skirts ex­tended at the front and rear where rub­bing is heav­i­est. The cylin­der block is in one piece, with bore lin­ers that ex­tend down into the up­per crank­case and a cen­tral cav­ity for the cam chain. It mounts onto the 12 studs with nuts on their tops that hold down the one-piece cylin­der head, with a gas­ket at the head-to-bar­rel joint. There are also two small bolts hold­ing the head to the bar­rel at the front and rear of the cam chain tun­nel.

The pis­tons have gen­tly-domed crowns with in­dents to clear the valves; spark plugs are off-cen­tre of the evenly-con­cave com­bus­tion cham­bers, tilted for ac­ces­si­bil­ity. The cylin­der head cast­ing in­cor­po­rates the lower half-jour­nals for the camshafts, four for each shaft. Each half-bear­ing is com­pleted by a top cap se­cured by two bolts, with num­bers and di­rec­tional ar­rows on the caps to en­sure cor­rect assem­bly; an oil-tight cover screws to the top of the head. The eight cam lobes press on bucket tap­pets that slide in the head me­tal and en­velop pairs of valve springs un­der col­lars fixed to the stems by split col­lets. Spring seats fit over the tops of the valve guides, which carry oil seals re­tained by ring-clips. A flange at the cen­tre of each camshaft car­ries a sprocket for the cam chain.

A car­rier bolted to the head holds a free-run­ning jockey sprocket to bear against the chain’s top run from above. Two more guide sprock­ets that bear against the out­side of the front and rear chain runs turn on nee­dle roller bear­ings on short shafts slot­ted into the top face of the bar­rel and held in place by rub­bers. The rear shaft ad­di­tion­ally sup­ports a car­rier for a wheel made of syn­thetic ma­te­rial held against the rear chain-run to main­tain ten­sion. A block bolted to the rear of the bar­rel con­tains the self­ten­sion­ing de­vice, a spring-loaded pusher with a rec­tan­gu­lar pad that bears against the chain. An­other plas­tic guide wheel be­tween the chain’s ver­ti­cal runs turns on a shaft held in notches by rub­bers at the crank­case joint face.

The Hy-vo pri­mary chain takes drive to a jack­shaft sup­ported by ball bear­ings in the up­per crank­case be­hind the crank­shaft. The re­ceiv­ing sprocket trans­mits drive to the shaft via a shock ab­sorber in­side it with four vanes and eight syn­thetic rub­ber in­serts. An out­put gear on splines at the right-side end of the shaft en­gages with a larger gear at­tached to the back of the clutch via a cush drive. Also on the shaft are a gear to drive the oil pump and a starter clutch mech­a­nism with three spring-loaded rollers. When the starter mo­tor (buried in the top of the crank­case) op­er­ates, it drives an idler gear turn­ing on its own short shaft, and that in turn drives the clutch’s gear, caus­ing it to lock to the jack­shaft.

The five-spring clutch has six plain driv­ing plates, plus one in­te­gral with the splined hub, and seven driven fric­tion plates. A worm mech­a­nism in the out­put sprocket cover on the right of the unit ac­ti­vates a rod slid­ing in­side the gear­box pri­mary shaft, ap­ply­ing force to the pres­sure plate via a ball bear­ing and mush­room pusher.

Ball races lo­cated by half-rings in grooves sup­port the gear­box shafts at their most loaded ends, be­hind the clutch on the pri­mary shaft and ad­ja­cent to the out­put sprocket on the left side for the sec­ondary shaft, while the other ends run in nee­dle rollers. The

‘THE OUTER CRANKPINS ARE AT TOP DEAD CEN­TRE WHEN THE IN­NER TWO ARE AT BOT­TOM DEAD CEN­TRE’

method of gear se­lec­tion is sim­i­lar to that in the big­ger fours – a cam drum car­ries one se­lec­tor fork, while two oth­ers en­gaged with it are car­ried on their own shaft. The drum is sup­ported in a roller bear­ing on its left side, where it is ac­ti­vated from the gear­lever’s shaft by spring-loaded claws en­gag­ing with six pins slot­ted into the end of the drum. The kick­starter shaft, with a ratch­eted driv­ing gear and re­turn spring on a plas­tic col­lar, is at the rear of the lower crank­case half. When CDI ig­ni­tion was in­tro­duced in 1981, the kick­starter was dis­pensed with, as was a spi­ral gear drive for a me­chan­i­cal rev-counter off the ex­haust camshaft.

The oil pump is a ro­tary type, un­like the gear pumps in ear­lier Z fours. Draw­ing from the wet sump through a gauze strainer, it pumps oil through a re­place­able fil­ter housed near the back of the sump, which has a re­lief valve in case of block­age. A pas­sage in the sump cast­ing then car­ries oil for­ward into crank­case drillings for dis­tri­bu­tion to the crank­shaft bear­ings, from where oil splashes up to the bores and pis­tons. From the two outer main bear­ings, oil as­cends ver­ti­cal pas­sages in the cylin­der bar­rel to the head, where its is led into the hol­low camshafts via the bear­ing jour­nals. Af­ter lu­bri­cat­ing the cam lobes and buck­ets, it falls down the cen­tral tun­nel, lu­bri­cat­ing the cam chain as it does. Oil is also pumped to both gear­box shafts. On top of the gear­box, a crank­case breather cham­ber with a re­mov­able cover set­tles out oil mist be­fore vent­ing to the air­box via a hose. To cut emis­sions, reed valves in the cam cover also vented to the air­box on Us-mar­ket mod­els from 1979.

‘BALL RACES LO­CATED BY HALFRINGS IN GROOVES SUP­PORT THE GEAR­BOX SHAFTS AT THEIR MOST LOADED ENDS’

Pri­mary drive jack­shaft with starter clutch Ig­ni­tion au­toad­vance unit Sta­tor of post-1977 sin­gle-phase al­ter­na­tor Stan­dard three-ring pis­tons with ex­tended skirts

Crank­shaft dif­fers from ear­lier Z fours’ built-up items – it’s a one-piece job with plain shell main and big-end bear­ings

Like the rest of the engine, the gear­box com­po­nents are rugged and re­li­able

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