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effective mass of a traditional valve with spring includes one-half of the valve spring mass for symmetric springs and all of the valve spring retainer mass. However, a desmodromic system must deal with the inertia of the two rocker arms per valve, so this advantage depends greatly on the skill of the designer. Another disadvantage is the contact point between the cams and rocker arms. It is relatively easy to use roller tappets in conventional valvetrains, although it does add considerable moving mass. In a desmodromic system the roller would be needed at one end of the rocker arm, which would greatly increase its moment-of-inertia and negate its "effective mass" advantage. Thus, desmo systems have generally needed to deal with sliding friction between the cam and rocker arm and therefore may have greater wear. The contact points on most Ducati rocker arms are hard-chromed to reduce this wear. Another disadvantage is the difficulty in incorporating hydraulic valve lash adjusters to a desmodromic system; thus frequent valve clearance (lash) adjustments are required. Additionally, each valve requires two lash adjustments - one for the opening rocker and another for the closing rocker. However, it is rare for most high RPM engines with conventional spring-loaded valvetrains to incorporate hydraulic lash adjusters – so they too require periodic checks and adjustments of valve lash.
332:(symmetric) profiles with identical positive and negative acceleration while opening and closing valves. However, some high speed (in terms of engine RPM) motors now employ asymmetrical cam profiles in order to quickly open valves and set them back in their seats more gently to reduce wear. As well, production vehicles have employed asymmetrical cam lobe profiles since the late 1940s, as seen in the 1948 Ford V8. In this motor both the intake and exhaust profiles had an asymmetric design. More modern applications of asymmetrical camshafts include Cosworth's 2.3 liter crate motors, which use aggressive profiles to reach upwards of 280 brake horsepower. An asymmetric cam either opens or closes the valves more slowly than it could, with the speed being limited by
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210:(TDC). This can lead to several problems. First, the valve does not completely return to its seat before combustion begins. This allows combustion gases to escape prematurely, leading to a reduction in cylinder pressure which causes a major decrease in engine performance. This can also overheat the valve, possibly warping it and leading to catastrophic failure. Second, and most damaging, the
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collides with the valve and both are destroyed. In spring-valve engines the traditional remedy for valve float is to stiffen the springs. This increases the seat pressure of the valve (the static pressure that holds the valve closed). This is beneficial at higher engine speeds because of a reduction
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With conventional cams, stress is highest at full lift, when turning at zero speed (initiation of engine cranking), and diminishes with increasing speed as inertial force of the valve counters spring pressure, while a desmodromic cam has essentially no load at zero speed (in the absence of springs),
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stress, and therefore is governed by both the moving mass and the cam contact area. Maximum rigidity and minimum contact stress are best achieved with conventional flat tappets and springs whose lift and closure stress is unaffected by spring force; both occur at the base circle, where spring load
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Before the days when valve drive dynamics could be analyzed by computer, desmodromic drive seemed to offer solutions for problems that were worsening with increasing engine speed. Since those days, lift, velocity, acceleration, and jerk curves for cams have been modelled by computer to reveal that
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The desmodromic system avoids some of the shortcomings of spring-loaded valves because it is not subject to the high loads associated with compressing stiff springs. However, it must still overcome the inertia of the valve itself, and that depends on the mass distribution of the moving parts. The
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processes helped to remove impurities from the metal in valve springs, increasing their life and efficiency greatly. However, many springs would still fail at sustained operation above 8000 RPM. The desmodromic system was devised to remedy this problem by completely removing the need for a spring.
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The common valve spring system is satisfactory for traditional mass-produced engines that do not rev highly and are of a design that requires low maintenance. At the period of initial desmodromic development, valve springs were a major limitation on engine performance because they would break from
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in the aforementioned valve float. The drawback is increased forces on all valvetrain components and increased friction and associated temperature and wear. It does not decrease power because nearly all work put into compressing the spring is later released as the spring is allowed to uncompress.
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Before numerical computing methods were readily available, acceleration was only attainable by differentiating cam lift profiles twice, once for velocity and again for acceleration. This generates so much hash (noise) that the second derivative (acceleration) was uselessly inaccurate. Computers
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Valve springs that do not resonate are progressive, wound with varying pitch or varying diameter called beehive springs from their shape. The number of active coils in these springs varies during the stroke, the more closely wound coils being on the static end, becoming inactive as the spring
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Fully controlled valve movement was conceived during the earliest days of engine development, but devising a system that worked reliably and was not overly complex took a long time. Desmodromic valve systems are first mentioned in patents in 1896 by Gustav Mees. Austin's marine engine of 1910
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In 1910 Herbert Austin decided to build a Marine engine that at the time was very advanced. It produced 300bhp and was installed in a speedboat called "Irene I" which was named after his eldest daughter who had married
Colonel Waite. The all aluminium twin ohv engine had twin magneto, twin
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curve produces a smooth acceleration curve while the third integral gives an essentially ideal lift curve (cam profile). With such cams, which mostly do not look like the ones "artists" formerly designed, valve noise (lift-off) went away and valve train elasticity came under scrutiny.
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at the beginning of the cycle and exhaust spent gases at the end of the cycle. In a conventional four-stroke engine, valves are opened by a cam and closed by return spring. A desmodromic valve has two cams and two actuators, for positive opening and closing without a return spring.
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Thus, neglecting all other factors, the faster an engine can be made to turn, the more power can be generated. Unfortunately, through at least the 1950s, valve springs often would fatigue and break when engines were operated for significant periods of time much above 8000
114:, leading to larger springs (with increased spring mass, and thus greater inertia), cam drag (as the valve springs require energy to compress, robbing the engine of power), and higher wear on the parts at all speeds, problems addressed by the desmodromic mechanism.
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For this reason, today as many as three concentric valve springs are sometimes nested inside one other; not for more force (the inner ones having no significant spring constant), but to act as snubbers to reduce oscillations in the outer spring.
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The specific purpose of the desmodromic system is to force the valves to comply with the timing diagram as consistently as possible. In this way, any lost energy is negligible, the performance curves are more uniform and dependability is
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compresses or as in the beehive spring, where the small diameter coils at the top are stiffer. Both mechanisms reduce resonance because spring force and its moving mass vary with stroke. This advance in spring design removed
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its load being entirely inertial, and therefore increasing with speed. Its greatest inertial stress bears on its smallest radius. Acceleration forces for either method increase with the square of velocity resulting from
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Azzariti, a short-lived
Italian manufacturer from 1933 to 1934, produced 173 cc and 348 cc twin-cylinder engines, some of which had desmodromic valve gear, with the valve being closed by a separate camshaft.
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is minimum and contact radius is largest. Curved (lever) tappets of desmodromic cams cause higher contact stress than flat tappets for the same lift profile, thereby limiting rate of lift and closure.
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The engineers that came after him continued that development, and Ducati held a number of patents relating to desmodromics. Desmodromic valve actuation has been applied to top-of-the-range production
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produced 300 bhp and was installed in a speedboat called "Irene I"; its all-aluminium, twin-overhead-valve engine had twin magnetos, twin carburettors and desmodromic valves. The 1914 Grand Prix
359:. High speed photography showed that at specific resonant speeds, valve springs were no longer making contact at one or both ends, leaving the valve floating before crashing into the cam on closure.
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permitted integration from the jerk curve, the third derivative of lift, that is conveniently a series of contiguous straight lines whose vertices can be adjusted to give any desired lift profile.
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In traditional spring-valve actuation, as engine speed increases, the inertia of the valve will eventually overcome the spring's ability to close it completely before the piston reaches
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between curved cam and flat tappet, thereby ensuring a more controlled acceleration of the combined mass of the reciprocating componentry (specifically the valve, tappet and spring).
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race at
Valencia, Spain in 2006. With the onset of the 800 cc era in 2007, they are generally still considered to be the most powerful engines in the sport, and have powered
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Title: The
Illustrated Encyclopedia of Motorcycles, Editor: Erwin Tragatsch, Publisher: New Burlington Books, Copyright: 1979 Quarto Publishing, Edition: 1988 Revised, Page 81,
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In contrast, desmodromic drive uses two cams per valve, each with separate rocker arm (lever tappets). Maximum valve acceleration is limited by the cam-to-tappet
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Valve float was analyzed and found to be caused largely by resonance in valve springs that generated oscillating compression waves among coils, much like a
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In modern engines, valve spring failure at high RPM has been mostly remedied. The main benefit of the desmodromic system is the prevention of
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Mercedes Benz's patent, showing the exact construction of the system used in the W196 and 300SLR. (requires Tiff reader)
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164:, a Ducati engineer, developed a desmodromic valve system for the Ducati 125 Grand Prix, creating the Ducati 125 Desmo.
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96:, "track" or "way"). This denotes the major characteristic of the valves being continuously "bound" to the camshaft.
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Ducati motocycle desmodromic valve timing engine parts: camshaft, valves, opening rocker arm and closing rocker arm
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cam dynamics are not what they seemed. With proper analysis, problems relating to valve adjustment, hydraulic
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to the 2007 MotoGP Championship and Ducati to the constructors championship with the GP7 (Desmosedici) bike.
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and Nagant (see
Pomeroy "Grand Prix Car") used a desmodromic valve system (quite unlike the present day
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is used to refer to mechanisms that have different controls for their actuation in different directions.
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that is positively closed by a cam and leverage system, rather than by a more conventional spring.
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introduced one of their final designs: a desmodromic four-cylinder, 2000cc engine for their last
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Ducati motorcycles with desmodromic valves have won numerous races and championships, including
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from 1990 to 1992, 1994–96, 1998–99, 2001, 2003–04, 2006, 2008 and 2011. Ducati's return to
313:. Computers have allowed for fairly accurate acceleration modelling of valve-train systems.
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Rivola, A., et al.: "Modelling the
Elastodynamic Behaviour of a Desmodromic Valve Train",
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An early solution to oscillating spring mass was the mousetrap or hairpin spring used on
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motorcycles since 1968, with the introduction of the "widecase" Mark 3 single cylinders.
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Proceedings of SMA2002 International
Conference on Noise & Vibration Engineering
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engines. These avoided resonance but were ungainly to locate inside cylinder heads.
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sports racing car of 1955 both had desmodromic valve actuation.
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838:"Desmodromology": for further investigation and visualisation.
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669:"Web Cam Inc - Performance and Racing Camshafts / Terminology"
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482:"The Art and Materials Science of 190 mph Superbikes"
294:, became things of the past without desmodromic drive.
253:. Please help to ensure that disputed statements are
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853:DVVA: Desmodromic fully Variable Valve Actuation
16:Reciprocating engine valve actuation mechanism
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305:, thereby avoiding elastic elements such as
487:. MRS Bulletin. p. 514. Archived from
36:Desmodromic poppet valve in a Ducati engine
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290:, push rods, rocker arms, and above all,
273:Learn how and when to remove this message
946:Crankcase ventilation system (PCV valve)
590:"4stHEAD Insight - Death of a Black Art"
249:Relevant discussion may be found on the
195:Comparison with conventional valvetrains
470:,16–18 September 2002 - Leuven, Belgium
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394:Famous examples include the successful
740:"MERC valve spring tests 1000-6000rpm"
84:, translated as "bond" or "knot") and
21:In general mechanical terms, the word
789:Greenpark-Productions. (2005-02-25).
717:. Glenbrook.k12.il.us. Archived from
402:race cars and, most commonly, modern
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55:allow the air/fuel mixture into the
638:"Duratec Engine Components 2009/10"
531:carburettor and desmodronic valves.
297:Today most automotive engines use
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554:from the original on May 25, 2012
153:racing car of 1954–1955, and the
1542:Engine valvetrain configurations
833:Desmo Information and Wallpapers
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126:Desmodromic poppet valve example
105:metal fatigue. In the 1950s new
1048:Overhead valve (pushrod) layout
480:Falco, Charles M. (July 2003).
421:990 cc engine in the GP3 (
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417:was powered by a desmodromic
411:Superbike World Championships
692:. Usq.edu.au. Archived from
415:Grand Prix motorcycle racing
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889:Internal combustion engine
643:. Cosworth. Archived from
617:www.tildentechnologies.com
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44:is a reciprocating engine
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1357:Diesel particulate filter
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1043:Overhead camshaft layout
816:October 9, 2007, at the
690:"Desmodromic Valve Gear"
68:The word comes from the
51:The valves in a typical
961:Core plug (freeze plug)
765:"ACLawrancePenguin.jpg"
518:"Austin Marine Engines"
334:Hertzian contact stress
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328:Today, most cams have
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400:Mercedes-Benz 300 SLR
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1202:Compression ignition
613:"Cam Design History"
528:on August 21, 2015.
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155:Mercedes-Benz 300SLR
1352:Catalytic converter
320:Integration of the
1547:Motorcycle engines
1478:Knocking / pinging
1070:Combustion chamber
671:. Webcamshafts.com
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148:Mercedes-Benz W196
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118:Design and history
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793:. Members.shaw.ca
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42:desmodromic valve
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1030:Cylinder head
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921:Balance shaft
919:
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883:
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771:on 2008-09-11
770:
766:
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746:on 2008-09-11
745:
741:
735:
732:
721:on 2012-08-04
720:
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696:on 2012-02-12
695:
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650:on 2013-06-18
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578:0-906286-07-7
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558:September 20,
553:
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516:Baker, John.
512:
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494:on 2007-03-07
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448:Engine tuning
446:
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406:motorcycles.
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299:overhead cams
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229:
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223:Disadvantages
222:
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203:at high rpm.
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1407:Electric fan
1207:Coil-on-plug
1133:Turbocharger
1128:Supercharger
1000:Main bearing
990:Firing order
980:Displacement
926:Block heater
910:Engine block
898:Part of the
897:
806:
795:. Retrieved
784:
773:. Retrieved
769:the original
759:
748:. Retrieved
744:the original
734:
723:. Retrieved
719:the original
709:
698:. Retrieved
694:the original
684:
673:. Retrieved
663:
652:. Retrieved
645:the original
632:
620:. Retrieved
616:
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596:. Retrieved
584:
568:
556:. Retrieved
545:
538:
529:
526:the original
521:
511:
502:
496:. Retrieved
489:the original
475:
467:
462:
443:Sleeve valve
431:Casey Stoner
408:
393:
372:
365:
361:
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346:
338:
330:mirror image
327:
319:
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296:
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198:
183:In 1959 the
182:
175:
170:
166:
159:
145:
141:
129:
103:
85:
73:
67:
50:
46:poppet valve
41:
39:
26:
23:
20:
1552:Formula One
1431:Lubrication
1395:Air cooling
1212:Distributor
1164:Fuel filter
1142:Fuel system
1123:Intercooler
1090:Timing belt
1080:Head gasket
1010:Piston ring
423:Desmosedici
376:valve float
368:Norton Manx
292:valve float
201:valve float
191:Barchetta.
151:Formula One
112:valve float
107:vacuum melt
24:desmodromic
1531:Categories
1483:Power band
1443:Oil filter
1417:Thermostat
1362:EGT sensor
1324:MAF sensor
1319:MAP sensor
1304:Air filter
1268:Alternator
1227:Spark plug
1159:Carburetor
1085:Rocker arm
1025:Valvetrain
956:Crankshaft
900:Automobile
797:2011-12-06
775:2008-06-25
750:2008-06-25
725:2011-12-06
700:2011-12-06
675:2011-12-06
654:2012-11-08
598:2011-12-06
498:2006-11-02
311:rocker arm
1217:Glow plug
1179:Fuel tank
1174:Fuel pump
941:Crankcase
263:June 2011
251:talk page
160:In 1956,
139:system).
64:Etymology
1516:Category
1461:Dry sump
1457:Wet sump
1448:Oil pump
1412:Radiator
1329:Throttle
1189:Ignition
1060:Camshaft
985:Flywheel
966:Cylinder
951:Crankpin
814:Archived
622:11 April
552:Archived
544:"Jansen
437:See also
382:Examples
244:disputed
189:O.S.C.A.
57:cylinder
1488:Redline
1372:Muffler
1273:Battery
1197:Magneto
454:Sources
341:galling
307:pushrod
288:tappets
172:better.
1511:Portal
1299:Airbox
1278:Dynamo
1005:Piston
995:Stroke
974:layout
902:series
576:
427:MotoGP
404:Ducati
357:Slinky
212:piston
178:Ducati
137:Ducati
133:Delage
92:δρόμος
86:dromos
80:δεσμός
74:desmos
72:words
1471:Other
1095:Valve
1065:Chest
648:(PDF)
641:(PDF)
593:(PDF)
492:(PDF)
485:(PDF)
303:valve
70:Greek
1453:Sump
970:bank
931:Bore
624:2018
574:ISBN
560:2016
504:rpm.
398:and
322:jerk
309:and
146:The
100:Idea
1438:Oil
1027:and
912:and
811:WMR
1533::
1459:,
972:,
615:.
550:.
520:.
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419:V4
352:.
40:A
1463:)
1455:(
976:)
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881:e
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76:(
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