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