HAR­LEY XLH IN BITS

The 1000cc ver­sion of the un­mis­tak­able V-twin from the last year of clas­sic iron Sport­sters

Classic Bike (UK) - - CONTENTS - WORDS: MICK DUCK­WORTH. PHO­TOG­RA­PHY: TIM KEETON

1000cc of Yank V-twin laid bare

First seen in 1957, Har­ley-david­son’s XL se­ries of over­head-valve V-twins for Sport­ster mod­els stayed in pro­duc­tion for al­most three decades. The orig­i­nal 883cc (70 x 97mm) ver­sion was based on the side-valve 750cc K-se­ries en­gine, Har­ley’s first unit-con­struc­tion twin in­tro­duced in 1952 and the ba­sis for KR ‘flat-head’ rac­ers that reaped Na­tional suc­cesses. The OHV Sport­ster XL was a re­sponse to the in­va­sion of the US by Bri­tish OHV 650cc twins that were faster and more nim­ble than the typ­i­cal Har­ley. The ba­sic XL was dropped af­ter 1959, hav­ing been joined the year be­fore by two Sport­ster vari­ants: the more tuned XLH and the even hot­ter pared-down XLCH com­pe­ti­tion twin. In 1966 a small batch of XLR TT rac­ers were built for TT dirt track events and the XR750 racer first seen in 1969 was de­rived from the XL for­mat. In that year, H-D was res­cued from col­lapse by the Amer­i­can Ma­chine & Foundry Co (AMF) and for 1972 the Sport­ster en­gine was en­larged to 998cc (81 x 96.8mm) to wring a claimed 61bhp from the aged de­sign.

The many vari­ants in­cluded the XLCR café racer ver­sion with a cu­ri­ous two-into-one-into-two ex­haust, a slow seller in 1977-1978, while a rorty lim­it­ededi­tion 70bhp twin-car­bu­ret­tor XR1000 with al­loy

cylin­der heads was snapped up in 1983. By then there had been a man­age­ment buy-out of the com­pany. The Xl-se­ries en­gine was fi­nally re­placed in 1986, when the Sport­ster ac­quired an 883cc ver­sion of Mil­wau­kee’s up­dated all-al­loy Evo­lu­tion en­gine.

The 1985 unit fea­tured here is from the last year of the clas­sic iron Sport­sters. Like all Har­ley V-twins since the 1909 orig­i­nal, its cylin­ders are dis­posed at 45°, in­line one be­hind the other, thanks to the ‘knife and fork’ ar­range­ment of the con­rods, with the bi­gend of the front cylin­der’s rod slot­ted in­side the forked end of the other. There are three bear­ings on the crankpin with 34 rollers as­sem­bled into two al­loy cages for the rear rod and 17 longer rollers in the front rod’s wider cage. The pin’s ta­pered ends are pressed into holes in the two iron fly­wheels and se­cured by nuts. The main­shafts are fixed in the wheel cen­tres by a sim­i­lar method.

The drive-side main bear­ings are two ta­pered roller units with their nar­rower sides fac­ing each other and sep­a­rated by a spacer snapped into a groove in a steel crank­case in­sert. The longer but less loaded tim­ing-side main­shaft is sup­ported in a caged roller bear­ing with long, small-di­am­e­ter rollers run­ning di­rectly on the shaft and its ex­treme end runs in a bush in the tim­ing cover. The crank­case con­tains com­part­ments for the crank­shaft, which has an oil baf­fle be­low it, and the trans­mis­sion. The left half in­cor­po­rates the in­ner pri­mary chain­case and a flange to carry the starter mo­tor in­tro­duced in 1968, while the right half in­cor­po­rates the tim­ing chest, ex­tended at the front to en­close drive for a gen­er­a­tor not fit­ted af­ter 1983. As well as com­plet­ing the tim­ing chest, the right-side en­gine cover has a purely cos­metic lower por­tion to give the unit a tidy ex­te­rior. An­other cover en­clos­ing the out­put sprocket to the rear of it is not shown here.

Each of the two valves per cylin­der is op­er­ated by its own short camshaft. Gears on the four shafts trans­mit drive, orig­i­nated by a pin­ion splined to the crank­shaft that meshes with a sec­ond, outer gear on the rear cylin­der’s inlet camshaft. The steel shafts turn in nee­dle roller bear­ings in the crank­case wall re­tained by two paired plates, plus any nec­es­sary shims, in­board of their lobes. Plain bushes sup­port the camshafts in the tim­ing cover. Roller tap­pets slide in al­loy guides, which have ears on their tops to an­chor them in their crank­case hous­ings. Cups on the tap­pets that en­gage with the

‘GEROTOR TYPE OIL PUMP RE­PLACED A GEAR PUMP IN 1978’

pushrods are on threaded stems with lock­nuts, so their height can be var­ied to ad­just valve clear­ance. The rods, with hard­ened but­tons top and bot­tom, are en­closed in plated tele­scopic tubes with springloaded in­ners and keeper clips, al­low­ing their tops to be dropped down so pushrods can be changed with the rocker boxes in place.

Re­cesses to clear the tubes are cast in the iron cylin­der bar­rels, which are held to the crank­case by studs, four for each, through base flanges. H-D spec­i­fied iron cylin­der heads for the XL af­ter prob­lems with al­loy heads on the ear­lier OHV Pan­head mod­els. They fit onto spig­ots sur­rounded by gas­kets, each be­ing held down to its bar­rel by four bolts. The com­bus­tion cham­bers are hemi­spher­i­cal and the three-ring pis­tons have flat-topped humps on their crowns and in­dents for valve clear­ance. The valve rock­ers are on spin­dles fixed in ‘shov­el­head’ al­loy rocker boxes bolted onto the heads while the valves, slid­ing in iron guides, have dou­ble springs re­tained by top caps and split col­lets. In 1977, a sin­gle Kei­hin CV car­bu­ret­tor re­placed a Bendix in­stru­ment.

The oil pump, a gerotor type that re­placed a gear pump in 1978, is at­tached to the un­der­side of the crank­case tim­ing chest. The two ro­tors, one for feed and a wider one for scav­eng­ing, are pinned to a ver­ti­cal drive shaft with a skew gear at its top that en­gages with a skew gear on the crank­shaft in­board of the drive out­put pin­ion. There is a switch for an oil pres­sure light and a pres­sure re­lief valve at the base of the pump, where oil drawn from the tank ex­its un­der pres­sure into an oil­way in the tim­ing cover lead­ing it to the crank­shaft drillings. A re­turn-side car­tridge oil fil­ter is housed in the part of the tim­ing cover pre­vi­ously oc­cu­pied by the gen­er­a­tor drive. Oil for the valve gear is pumped to unions on top of the crank­case, then car­ried to the rocker boxes where it en­ters the hol­low rocker spin­dles. Drains be­side the valve guides lead oil down drillings to holes in the lower cylin­der bores, where it splash­lu­bri­cates the bot­tom-end be­fore be­ing scav­enged back to the tank.

A triplex pri­mary chain drives the outer clutch drum, which is riv­eted to the com­bined sprocket and starter gear. A dou­ble-row ball race at its cen­tre runs on a sleeve in­te­gral with the main­shaft first-gear pin­ion and sup­ported by a cir­clip-lo­cated ball race in a re­mov­able gear­box ac­cess plate be­hind the clutch, known as the

trap­door in Har­ley ter­mi­nol­ogy. Able to turn on the main­shaft thanks to a pair of caged nee­dle-roller bear­ings in­side it, the sleeve has fine splines on its end to carry the clutch cen­tre, which is se­cured by a nut and tab washer.

Six fric­tion plates en­gaged with the drum and six plain plates en­gaged with the cen­tre are held to­gether by a pres­sure plate and a di­aphragm spring re­tained by a large cir­clip. Clutch op­er­a­tion is by a ball-and-ramp mech­a­nism mounted in the al­loy pri­mary drive cover. The drive out­put sprocket is fixed on splines at the other end of the main­shaft, which is sup­ported in a caged nee­dle roller bear­ing. The layshaft di­rectly be­low has a nee­dle roller unit at each end. The gearchange pedal, on the left side from 1975 to com­ply with leg­is­la­tion, is on a long shaft that runs through the gear­box. A ball-ended arm on it en­gages in a ratchet mech­a­nism to ro­tate the ver­ti­cally-mounted cam plate con­trolled by a pawl mech­a­nism, si­t­u­ated at the front of the box. Two se­lec­tor forks are mo­ti­vated by the cam slots and there is a de­tent peg un­der the cam plate, held against it by two coil springs.

Elec­tronic ig­ni­tion re­placed a points-and-dis­trib­u­tor sys­tem in 1979. The trig­ger unit is housed in the tim­ing cover and driven off the end of the rear cylin­der’s ex­haust camshaft. Tim­ing can be checked us­ing a strobe light and marks vis­i­ble on the crank­shaft through an in­spec­tion plug on the right-side of the crank­case above the pri­mary chain­case.

Main pic: Dis­tinc­tive ‘knife and fork’ con­rods in­ter­lock. Above left: Tele­scopic tubes al­low the pushrods to be changed with the rocker boxes in place

Oil pump has two ro­tors: one for feed and a wider one for scav­eng­ing

Cast iron cylin­der head fea­tures hemi­spher­i­cal com­bus­tion cham­bers and two oil drain pas­sages

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