DUCATI BEVEL TWINS 1971 TO 1986

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1 The engine breather valve exited into the rear air filter box. Engine The engine number was always stamped on the left rear crankcase half, beginning at A DM750 was stamped on the right crankcase. 750 engines also included a pair of matching assembly numbers (between ) between the cylinders, and an A or B stamped above the clutch cover to indicate A or B pistons and barrels. These early sand-cast crankcases not only had deep recesses but the casting from the kick-start shaft to the right rear lower engine mount was solid. The crankcase halves were also held together by only three 10mm bolts. The casting around the main bearings was also more substantial than on later production engines, as were the outward strengthening ribs. All Ducati engines came with a lead seal wired to two drilled Allen bolts underneath the crankcases, and the existence of this seal is the only way to positively identify whether an engine has been apart at any stage. The first few numbers identified prototype engines, and differed to the production versions in a number of details. The camshaft bevel-gear drive of the first 750 engines was notable for an absence of timing marks, but this was soon rectified. All these engines though used the cast tulip shaped lower bevel gears that were hollow underneath. They were more tapered on the top, and lighter than later bevel-gear sets but probably more expensive to manufacture as they were cast then machined. Both the early and later bevel gears carried the same part number ( ). The crankcase breather consisted of a plastic labyrinth and polished aluminium housing at the rear of the right crankcase half. A Ø18xØ24x270mm black plastic tube ran to a flapper valve in the rear air filter box. The hose was supplied by Nava, and all bevel twin Ducatis featured this black plastic Nava breather hose, in varying lengths A cutaway of the 750 GT engine. Above and opposite: 750 engine drawings. for a particular application. The distinctive cast and polished outer engine covers included a clutch cover without an inspection plate, alternator cover with a shorter boss to accommodate the shorter kickstart shaft, and a floating tachometer drive (inherited from the singles) from the front cylinder head. Other engine differences included a different 22

2 also better located on the 860 because the retaining flanges used four, rather than two, M6x20mm screws. There were other improvements Square-case crankcase halves had the matching numbers underneath. Exploded view of the 860 engine. 86 Some 860s had the engine number stamped on the lower crankcase. The early production 860 GT had a single front disc brake and kicked-up seat. redesign than merely the shape of the outer engine covers, and, apart from the gearbox, most of the internal parts were not interchangeable with the 750. Central to the redesign was a new bevel-gear drive to the two vertical shafts. Instead of the bevel-gear at the crankshaft, a keyed, straight-cut gear drove two further spur gears mounted onto an outrigger plate. A 22-tooth gear drove the oil pump, while the other (24-tooth) drove two 36-tooth spur gears keyed to a 23-tooth bevel gear. The right end of the crankshaft and two 36-tooth gears were supported on an aluminium outrigger plate securely bolted to the crankcase half by three 8x40mm and one 8x35mm bolts. The crankshaft spun in a 20x47x14mm roller bearing, and the two vertical shafts in 15x42x13mm roller bearings. These two straight-cut gears were keyed to bevels that drove the two vertical shafts. It was a far easier system to assemble because the straight-cut gear meshing was unaffected by sideways movement, and the two bevel-gear shafts could be set up independently. The 860 arrangement was also superior as crankshaft end play didn t affect the camshaft timing. As there was the outboard plate supporting the crankshaft and bevel-drive gears, there was no longer an outside bearing incorporated in the alternator cover. The lower camshaft bevel-gears were The 860 alternator still sat outside the camshaft drive. Early 860s still used the small 750-watt alternator, but most (like this example), had a larger alternator. incorporated into the 860 redesign. The oil pump drive gear was no longer machined as part of the crankshaft, but was a keyed-on spur gear (machined with the crankshaft timing gear). With the new bevel-gear drive there was no longer any necessity for a central gear, and this allowed the fitting of an oil filter in addition to the plastic gauze strainer in the sump and the centrifugal sludge traps in the crank webs. It may not have been a full flow filter, but it was an improvement over the 750, that relied purely on the gauze sump strainer and the crankshaft sludge traps. As the 860 oil filter was a bypass type, and filtered only a small proportion of the oil on the way to the rear cylinder head, it s usefulness was debatable. This filtered oil then dropped onto the camshaft drive gears. The oil filter was located by a black pressed steel cover, and sealed with a rubber ring. The steel cover had a tendency to warp if over tightened, leading to oil leaks. The oil pump was

3 There were only minor changes in specification to the cylinder head. New O-rings, with a different heat grade, were used in the valve guides (Corteco or Viton), and the camshaft bearing supports were generally the less angular 900 SD type ( ). These had an advantage in they could be rotated for rocker pin removal, but some earlier 1978 engines retained the previous type. As before, both Dellorto 40mm and 32mm carburettors were specified, most receiving the 32mm carburettors as standard fitment. The 40mm carburettors still had open bellmouths, often with the earlier wire mesh. Following the changes to the camshaft gear support plate that had appeared on the 900 GTS, the Super Sport also received the new plate ( ). The 460mm (up from 440mm) crankcase breather hose now 142 The 750 SS retained the earlier 750 camshaft bearing housings. 40mm carburettors were always an option; now with aluminium mesh on the bellmouth. incorporated an internal spiral spring. The second breather hose (to the front air filter box) was shorter than before at 690mm but the breather chamber was still in the seat base Super Sports also came standard with Lafranconi mufflers, although the longbracket Contis were an option. Some 1978 Super Sports were fitted with 860 GT or GTS header pipes, and generally the front exhaust nut was drilled and lock wired. Most Super Sports left the factory with 32mm carburettors and silver-painted steel air filter boxes. The left crankcase no longer had a plug for the ignition wires under the front engine mount, all the ignition leads were now included in a new engine clutch cover ( ). This also had an additional M24x1.5 plug for ignition pick-up inspection. The ignition system was the Bosch as outlined in chapter five, in the section on the 900 SD, and included the hotter Champion L88A, or Bosch W7B (W175T35), sparkplugs of the 900 SD. Ignition leads and sparkplug caps were as before, black with rubber KLG. Towards the end of 1978, Bosch plastic electrically-suppressed sparkplug caps started to appear on some Super Sports, these particularly unreliable if the bike was ridden in the rain. If possible, try to fit the KLG type that work well enough, and look right on these engines. All Super Sports were fitted with a 15-tooth countershaft sprocket (although the 16-tooth was still an option), with a 36- or 38-tooth rear sprocket. The 38-tooth provided considerable undergearing, and wasn t particularly suitable for the Super Sport. The chain was a Renold 5 8x 3 8- inch with 102 links. Lafranconi mufflers were fitted on most 1978 Super Sports, but the long bracket Contis were listed as an option. The new clutch cover included an additional inspection plug. Frame and cycle parts Super Sport frame numbers continued in the DM 860SS sequence from around , still with the same DGM OM frame homologation number. The silencer homologation plate with the numbers DM 860 S E3 9R was still mounted on the right side. Initially, the frame was painted silver as before, but had different brackets for mounting the Bosch ignition components and footpegs. Those 1978 examples with the earlier engine (with crossover gearshift), retained the earlier frame and footpeg mount, but a study of frame numbers indicates very little overlap. Most (if not all) 900 SSs with the earlier frame type had frame numbers prior to The 1978 The 900 SS frame number continued the earlier series.

4 MIKE HAILWOOD REPLICA The replica received a new Marzocchi fork, shock absorbers, wheels and brakes. Most of these changes were to follow fashionable trends, but there were a couple of genuine improvements. The Brembo brake calipers were positioned behind the fork legs, the axle still going from the right. Like the first 750 Super Sport, the M6x7mm fork oil drain plugs were in front of the fork legs. A small yellow Marzocchi decal was on the base of the left leg. Examples with an hydraulic clutch had black Verlicchi adjustable handlebars. The Verlicchi throttle included start and stop switches. The Verlicchi handgrips were unchanged. The taillight was much larger. Also unchanged was the Nippon Denso light/horn switch. The aluminium foot levers were the same as for the 900 S2. The 1984 MHR had the brake calipers behind the black fork legs. The Marzocchi suspension was shared with the final series 900 S2, the front fork with 38x590mm fork tubes, 221mm hydraulic rods, black-painted fork legs, and rear-mounted brake calipers. While all the fork legs were painted black on these 900 Replicas, during 1984 the finish became matte black rather than the earlier crinkle type. At the same time, the top fork leg oil seals were updated to improve the fork action. These no longer included the outer fork cups, but an internal rubber type offering less fork tube resistance. At the same time, the forks gained air caps, with a Schrader valve on the top of each leg, and a single fork seal replaced the previous two. The shock absorbers were 330mm black-bodied, oleo-pneumatic Marzocchi AG Strada with black 175

5 Chapter 9 Engine restoration In the earlier edition of this book, this chapter was not intended as an engine rebuilding guide. However, with a workshop manual no longer readily available, it seems appropriate to include engine rebuilding here. The basis for this chapter was the rebuilding of an engine for a GT, with square-case and desmo material covered by a SD Darmah. Engine disassembly hasn t been dealt with in detail, but any special tips will be mentioned in the assembly process. As the basic design shared so many features from the first 750 until the final Mille, many of the later engine components can also be used in the earlier engines. Thus, the stronger three-dog gearbox is a direct replacement for the earlier six-dog type, and many clutch components are interchangeable. CRANKCASES, CRANKSHAFT, CLUTCH AND GEARBOX Because there are so many similarities between the three engine types (round-case, square-case, and Mille), it s useful to take an overall look at these engines before delving into specific types. All bevel twins share the same design of vertically-split crankcases with a five-speed direct 200 type gearbox. The ball bearings used on all the shafts were the same from The production 750 round-case crankcase of The 750 oil sump was separate, with the gearbox layshaft above the mainshaft. The 900 square-case crankcase of 1978 was similar, but the castings were smoother and the ignition outlet hole was blanked off. These early Bosch cases still had the mounts for the Ducati Elettrotecnica ignition. The 900 crankcase was very similar internally to that of the 750. This 1978 engine has the kick-start stop.