The Scrambler is proving one of the most effective marketing operations in the whole motorcycling industry. But this kind of “operation nostalgia” can only be carried out with solid chances of success by Makes like Ducati or Triumph, with strong tradition and, most important, a past model from which draw a direct line of inspiration in order to renew the magic of the “good ole days” by refreshing the look, the general allure and the name.

The car industry tried a number of such operations down memory lane, but only a limited number was successful, and the list of sad flops is impressive, given the names and the models involved, stating from the VW New Beetle. Ducati Scrambler is a perfect example of “operation nostalgia”, intended to revamp the myth of the original, born in the late ‘60s, as a dirt-track racer derived model inspired by US importer Mike Berliner and that remains one of the neatest looking and most extrovert bikes ever, lean, arrogant and daring.

In addition to the right name and look, the new Ducati Scrambler features an additional “nostalgic” factor: it is the last and only Ducati model powered by the glorious Ducati SOHC, aircooled, two valve, 90 degrees V Twin designed by Dr. Fabio Taglioni. The line that connects the original Ducati 500cc Pantah Twin to the present 800cc Scrambler stretches over 40 years, marked by a sequel of remarkable successes, both in the sport and on the international markets.

The Pantah Twin represents the pivotal factor in the construction of the present and very brilliant condition of Ducati Motors. The Pantah Twin completely rebuilt the image of the Make in terms of quality and reliability, finally putting an end to the era of the disintegrating crank assemblies (rods, needle cages, main bearings, you name it) that almost wiped Ducati out for good in the ‘70s. The Pantah proved so substantially reliable that it was elected to become the platform on which was derived a sequel of engines that grew from the original displacement to 1100cc and, even more meaningful, also was the foundation on which the Four Valve Desmo family of supreme twins was erected, all the way to the present 1198 Testastretta.

The story of the Pantah Twin overlaps with the personal story of the man who started his working career at Ducati in time to contribute to detail the original project and, from then on, progressively take it in his hands and lead it thru its multi faceted evolutions. To the present 800cc Scrambler unit.

The man is Gigi Mengoli, Chief Engines Project Engineer. He did all the hard work, both in the old days at the drawing board, translating theoretical concepts, like the Four Valve Desmo distribution, into fine working and reliably performing pieces of mechanical excellence, and today, at the computer, conceiving the Desmo Variable Timing Distribution. Gigi loves and is very proud of his job and he also loves Ducati, he always did and he remembers the old days with Dr. Taglioni with great pleasure. Something I fully agree on.

“Dr. Taglioni was a great leader and teacher, always open to share his enormous knowledge with his assistants. All he asked in return was passion, determination, hard work and loyalty. He loved the way I worked at the drawing board and he wanted me in the team that designed the Pantah 500 Twin.

The project was treading on new ground, being the first Taglioni’s engine (forget the GTV 350-500 parallel twin, he hated that engine) departing from the traditional interference fit crankshaft featuring roller or ball bearings at the main ends and needle cages at the conrods big end, two stroke style.

Finally Ducati was moving into the very reliable realm of solid crankshafts and plain bearings. Not fully, though. He still loved those beautiful “angular contact” ball bearings, at the time only coming from US Marlin-Rockwell, and he also thought that the hybrid solution might make the oiling system life easier. But switching to the solid crank assembly was not a problem. Actually there were a few more.

First, there was a specific issue from the Ducati sales department about making our engines mechanically less noisy and since the noise was generated by the gears of the primary transmission. So we had to switch to a primary transmission by Hi-Vo chain. Not a minor modification because the engine had to be revised in all distribution components since its rotation had to be inverted. Then first test showed that things were not as smooth and we had to switch back to gear type primary transmission.

The Pantha 500 engine proved super. Dr. Taglioni poured in the project all the very positive experience gathered from the short stroke version of the “bevel gear” 750 V Twin that raced the Imola 200 in 1973. This meant a largely revised thermodynamic section featuring valves set at a 60 degrees included angle and slightly revised inlet runners profiles. The Pantah 500 was good for 50+ Hp in properly civilized conditions. From then on I handled the progressive evolution of the engine to 650 and 750cc, including the TT2 winning 750 F1 very sporty model. The most radical evolution came when we developed the Paso 750 version, with the head of the vertical cylinder turned 180 degrees to make it suitable for central induction, via a Weber twin barrel carburetor.

That was more challenging than it might sound because the rearward facing exhaust port developed overheating problems due to the cooling airflow proving inadequate. But we managed. While the evolution of the Four Valve Desmo units absorbed most of the energies of the Engine Project and Development Department, the SOHC air cooled two valve desmo grew in displacement alongside, up to 1100cc, untill new emission regulations struck and I had to go back to the drawing board.

The new major evolution were the 696 and the 796 versions, there our SOHC aircooled unit proved that there was still potential in the Pantah design, since both proved properly clean and very brilliant, exceeding 100Hp/liter specific output. The major evolution came from tightening the included angle of the valves, now down to 58 degrees, 2 less than it was on the original Pantah heads, plus properly redesigned piston top and inlet and exhaust runners.

These units were the foundation on which we developed the present 803cc unit that powers the Ducati Scrambler. In this case top power was not the issue, “adequate power” was all that was needed. But with the present regulations, even the 75 Hp we extracted were an interesting challenge for a two valve induction, air cooled twin. The primary research was devoted to optimizing the turbulence in the combustion chamber, a swirl mode turbulence, and here at Ducati we have a long experience thanks to Dr. Taglioni’s research in the domain. Runners configuration, squish area and piston top design were all very accurately defined and I believe that the engine is proving smooth, strong and clean. In addition we had to optimize a few details of the heads configuration to improve cooling.

I am very proud of the final result, and its 399cc little brother, powering the Scrambler Sixty2 is already outselling all the competition in the displacement class”.

Gigi Mengoli poses with the two engines he contributed to bring to life and final definition and validation and that represent the two extremes of the evolution of the Ducati air cooled SOHC two valve 90° Vee Twin, the 802cc of the Scrambler (left) and the original Pantah 500 (right).

Two of the original sketches by a very young Gigi Mengoli that represent the early steps of development of the Pantah 500 project. By switching from the traditional interference fit to a solid crankshaft, Dr. Taglioni drastically solved the reliability problems that plagued the old Ducati singles and the bevel gear 90° Vee Twin and that were caused by the poor quality of the assembly and quality control procedures: the interference fit units were never checked for proper squaring off and correct alignment of the halfshafts, thus the wobbling crankshaft would just kill needle cages, rods or main bearings in a few thousand miles.

The Scrambler SOHC V Twin is a vastly and very accurately evolved engine and it shows it both in the outer look and in a number of inner details. The new alternator cover hides a much larger and more powerful unit. Castings also are of superior quality, but vital measurements are unchanged.

Same as that of the alternator, also the clutch cover appears much larger to host a much more capable clutch that finally closes the case generated by the traditionally high lever effort caused by a too small clutch diameter inherited from the most unfortunate Ducati 350-500 GTV parallel twin. The old distribution belts covers designed by Dr. Taglioni were very elegant and for the first time the new ones look almost as good.

Outer and inner views of the right crankcase. All vital measurements have remained constant with the only exception of the gearbox shafts center-to-center that was modified from 57 to 61 millimeters way back when the engine grew to 750cc, to make the transmission components beefier to properly handle the increased torque. The oiling system was amply improved in terms of flow and with the addition of an oil radiator, the connections to the lines going and coming from the radiator are visible on 4A, at the right-lower end.

The quality of castings is enormously improved, courtesy of the Italian branch of Alcoa that introduced very advanced casting processes and a high tensile alloy that radically solved all the old cracking problems. In addition, modern computerized tooling delivered supreme machining qualities, both in precision and finishing.

Talking of precision machining, not only it sent gaskets into retirement, but also required that contact surfaces, like in this case the matching edges of the two half crankcases, be machined to obtain a slightly treaded surface in order to offer better grip to the sealants that replaced gaskets.

Main bearings are still of the same, old angular contact, ball type. The main novelty is that now they are made in France and their design include the retaining thrust washer. The bearing cage is metallic now, given the lower RPM, in the original hi-performance MRC manufactures bearings adopted by Dr. Taglioni they were in phenolic composite material for much higher rotational speed limits.

The 802cc crankshaft complete with its main bearings. Main journals diameter is 35mm, crank pin journal is 40mm, same as on the old Pantah 500.

Axial view of the crankshaft with the main bearing in place.

Conrod center-to-center measurement remains the original 124 millimeter as is the I type design.

The real innovation is represented by the cap of the conrod, that now are of the cracked type in order to obtain a perfect alignment when bolts are tightened, with no need for the insertion of dowels.

The heads of the 802cc engine represent a meaningful evolutionary step in the refinement of the Ducati air cooled, 2 valve induction SOHC unit. Valves are set at 58 degrees included angle for a compact combustion chamber profile and equally important the design of the side squish bands keeps the turbulence (swirl) under full control for a complete combustion of the inhaled charge, and thus for both good performance, reduced fuel consumption and clean exhaust. The engine conforms to Euro 3 but will soon be upgraded to Euro 4.

The latest cylinders (and heads) feature cooling fins that are more extended than they were in previous editions and the Scrambler unit received specific attention since the models is being produced in Thailand for the far east and Pacific area markets, where motorcycles have to face some hard service conditions. Again, castings and machining are of a quality far superior not only to the original Pantah stuff, but even to much more recent versions. Bore measurement is 88 millimeter.

Pistons have a smoothly profiled dome at the top and moderately deep valve pockets that do not interfere with the cleanliness of the profile and with the control of the turbulence. The dome contributes to create a tumble effect in the incoming flow that combines with the natural swirl turbulence for a very effective combustion.

Aside of being desmo actuated, the valves are of a very standard type, diameters are 44 millimeter inlet and 38 millimeter exhaust, stems are 7 millimeter in both cases.

The desmo camshaft features moderate lift and overlap, for a smooth, torquey unit that conforms with present exhaust emission regulations just about anywhere. Desmo valve train uses traditional valve opening and closing rocker arms. Gigi Mengoli is ready to swear on a stack of Bibles that desmo valves maintenance is only fractionally more complex and more expensive than regular “spring valves" maintenance.

To set the whole distribution train, and the engine, at its sharpest efficiency, Gigi Mengoli developed a very effective procedure. Here you see the camshaft of the vertical cylinder sitting atop the cam cover to show how the sharp tuning procedure must start. The camshaft features a notch carved on the outer ring at the end opposite to the distribution belt sprocket. The cylinder must be set with the piston at TDC and then the camshaft must be micro-rotated till the notch is aligned to the threaded hole at the bottom of the cam cover.

In order to set the notch of the camshaft in the proper position, the camshaft must be set free from the driving sprocket. Mind you, only a rotation of a few degrees is requested, here I am talking of fine tuning, since the distribution is already in proper setting. The sprocket is held in place by three screws that must be released. When the notch is aligned, it must be held in place by inserting a screw in the threaded hole and tighten it to lock the camshaft. At this stage the sprocket will re-set automatically thanks to the oval slots that allows its micro-adjustment to the proper position sprocket-to-camshaft relationship.

Secondary air injection is fundamental to achieve legal emission levels according to Euro 3 standards and soon progress to Euro 4. On the front of the vertical cylinder is located the valve of the secondary air that is leaked into the exhaust port.

The larger displacement editions of the Ducati aircooled SOHC V Twin all suffered from overheating of the  exhaust port area. This 802 version features cooling fins and slots all the way to the inner portion of the runner.

Big surprise from the 399cc unit of the Scrambler Sixty2: the crankshaft is of the interference fit kind, and this is rather extreme given the very short stroke, 49mm, that creates the conditions for the crankpin to overlap the main journals, that retain the 35 millimeter diameter since here too are used the tried and true angular contact ball bearings in 35mm by 80mm by 21mm size.

At the big end, the rods use plain bearings, half shell type , same as those used on cap type conrods since full ring bushings do not offer advanced tri-metal bearing surfaces that are capable to stand much higher specific loads than even the best bushings.

The crankpin has a diameter of 32 millimeter, and that generates a 9 millimeter overlap to the 35 millimeter main journal, well visible in the axial view of the halfshaft. A rigorous precision is requested by the press fit of the three components of the crankshaft (plus the two rods) in order to grant the correct alignment of the oiling lines. An automated procedure was developed to grand the highest possible standard.  

courtesy of webmatter.de