Motorcycle Gearbox

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Sequential manual transmission shifting animation

A sequential manual transmission, also known as a sequential gearbox, or a sequential transmission, is a type of non-synchronousmanual transmission used mostly for motorcycles and racing cars.[1] It produces faster shift times than traditional synchronized manual transmissions, and restricts the driver to selecting either the next or previous gear, in a successive order.

Motorcycle Gear and Motorcycle Apparel. Rocky Mountain ATV/MC understands the different needs for sporting, cruising and touring and we supply the motorcycle riding gear for them all. Whether you’re a casual cruiser, long range sport biker or touring rider. All that you need to do to shift gears on a motorcycle with a semi-automatic transmission is throttle the engine and use the gear shift. On a semi-automatic, the clutch is tied in to the gear shift, so using the gear shift activates both controls at once. 2 Turn the bike on. As well as supplying complete motorbike gearsets, we also can also provide alternate ratios for standard motorbike gearboxes by supplying adjusted ratio gear pairs as a direct replacement to the standard gear ratio. Nova also carries a wide range of individual gears for spares, please contact us for availability and prices.

Design[edit]

A simple transmission ­A motorcycle engine can create an enormous amount of power, which must be delivered to the wheels of the vehicle in a controllable way. The motorcycle transmission delivers power to the rear wheel through a series of structures that include the gearset, the clutch and the drive system.

Gear shift lever on a motorcycle (above the toe of the rider's boot)

A sequential manual transmission is unsynchronized, and allows the driver to select either the next gear (e.g. shifting from first gear to second gear) or the previous gear (e.g., shifting from third gear to second gear), operated either via electronic paddle-shifters mounted behind the steering wheel or with a sequential shifter. This restriction avoids accidentally selecting the wrong gear; however, it also prevents the driver from deliberately 'skipping' gears.[2] The use of dog clutches (rather than synchromesh) results in faster shift speeds than a conventional manual transmission.[3][4]

On a sequential manual transmission, the shift lever operates a ratchet mechanism that converts the fore-and-aft motion of the shift lever into rotation of a selector drum (sometimes called a barrel) which has three or four tracks machined around its circumference.[5] Selector forks are guided by the tracks, either directly or via selector rods. The tracks deviate around the circumference and as the drum rotates, the selector forks are moved to select the required gear.[6]

A sequential manual transmission is not to be confused with a 'sequential' shifting function sometimes fitted to hydraulic automatic transmission, marketed with terms such as 'Tiptronic' or 'SportShift'. This function allows the driver to select the previous or next gear through the use of buttons or a lever (usually near the gear shifter or steering wheel); however, the mechanicals of the transmission remains unrelated to a true sequential manual transmission.

Usage[edit]

Most motorcycles use a sequential manual transmission. The rider controls the gear shifter with their foot, allowing their hands to remain on the handlebars, and gear selection uses a layout of 1 - N - 2 - 3 - 4 - 5 - 6 (in a 6-speed gearbox, for example).[7] However, most modern motor scooters do not use a sequential manual transmission, instead using either a hydraulicautomatic transmission, or a belt-driven or chain-drivencontinuously variable transmission. Some older motor scooters, however, may use a semi-automatic transmission with an automatic centrifugal clutch, but will still retain the conventional foot-operated gearshift lever, such as the Honda Super Cub.

The first proper sequential manual gearbox used in a racecar was with the in 1946,[8] followed by the infamously unreliable Queerbox design, pioneered by Richard Ansdale and Harry Mundy, which was used in various Lotus Grand Prix racecars during the late-1950s and early-1960s, beginning with the 1958 Lotus 12, and is technically the first proper 'sequential' gearbox used in a racecar.[9] Most racing cars also use a sequential transmission now (either via a sequential shifter lever or with paddle-shifters),[10] rather than the old H-pattern stick shift, beginning with the paddle-shifted Williams FW14Formula One car in 1991, which used a sequential drum-rotation mechanism.[11][12]

The first modern sequential manual gearbox with a manual shift lever was used in the 1990 Peugeot 905Group Csports car, followed by the Ferrari 333 SPLMPracecar and CARTChamp Cars/Indycars in 1994 and 1996,[13] and then the McLaren F1 GTR, Mercedes-Benz CLK GTR, Porsche 911 GT1, and Panoz Esperante GTR-1GT1racecars in 1996 and 1997. This was closely followed by WRCRally cars in 1997, 1998, and 1999, and also the Porsche LMP1-98, Nissan R390 GT1, Toyota GT-One, and the BMW V12 LM and LMRLe Mans Prototyperacecars in 1998 and 1999.

Touring cars have also used sequential manual gearboxes; starting with the European DTM series in 2000, which used it for 12 seasons, until a switch to a paddle-shift system in 2012. The Australian V8 Supercars series started using sequential manual gearboxes in 2008, after switching from an H-pattern manual gearbox.

NASCAR is due to introduce a 6-speed sequential manual transmission with their Gen-7 car in 2022, after using a conventional 4-speed H-pattern manual transmission for many years.[14][15][16][17]

Due to the high rate of wear and abrupt shifting action, sequential manual transmissions are rarely used in passenger cars, albeit with some exceptions.

Motorcycle Gearbox With Reverse

See also[edit]

References[edit]

  1. ^Cameron, Kevin (1998). Sportbike Performance Handbook. Motorbooks. p. 82. ISBN9780760302293. Motorcycle transmissions and the latest auto-racing gearboxes are of the sequential type
  2. ^'Gearbox technologies'. www.drivingfast.net. 27 October 2016. Retrieved 2 January 2020.
  3. ^'How Sequential Gearboxes Work'. www.howstuffworks.com. 4 April 2003. Retrieved 2 January 2020.
  4. ^https://www.caranddriver.com/reviews/a15136822/bmw-m3-smg-short-take-road-test/#:~:text=SMG%20first%20appeared%20in%20Europe,traditional%20synchronizers%20and%20shift%20forks.
  5. ^'How Sequential Gearboxes Work'. www.howstuffworks.com. 4 April 2003. Retrieved 2 January 2020.
  6. ^'BMW M3 SMG - Short Take Road Test - Auto Reviews'. Car and Driver. Archived from the original on 2009-04-08. Retrieved 2011-08-29.
  7. ^Cameron, Kevin (2009), Top Dead Center 2, Motorbooks, p. 58, ISBN9780760336083
  8. ^'Cisitalia 360 Grand Prix Car'(PDF). stevemckelvie.files.wordpress.com. Archived from the original(PDF) on 27 February 2015. Retrieved 17 July 2018.
  9. ^https://www.highpowermedia.com/Archive/sequential-gearbox-origins
  10. ^https://www.iea.lth.se/publications/MS-Theses/Full%20document/5263_full_document.pdf
  11. ^https://www.f1technical.net/features/10705
  12. ^https://auto.howstuffworks.com/sequential-gearbox.htm
  13. ^https://www.lolachampcar.com/Gearbox.htm
  14. ^https://www.foxnews.com/auto/nascar-transmission-next-generation
  15. ^https://www.autoblog.com/2020/01/19/nascar-next-gen-car-testing-six-speed-sequential-transaxle-wider-tires-bigger-wheels-new-aero/
  16. ^Wilhelm, Chase (March 3, 2020). 'William Byron details learning experience after Next Gen test at Fontana'. NASCAR.com. NASCAR Digital Media, LLC. Retrieved March 5, 2020.
  17. ^Smith, Steven Cole (December 30, 2019). 'Next-Gen: What We Know about NASCAR's New Car'. Autoweek. Retrieved March 3, 2020.
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Motorcycle engines do not produce all their power at all RPM's. There is very little power at idle and the power goes up as the engine RPM goes up. At a certain RPM, which is different for each engine, the power goes up quickly and continues to increase until it hits the maximum RPM for that engine. This is called the 'Power Band'. Generally small, high revving 2/strokes have a narrow power band, requiring lots of gears in the gear box. Large, low revving 4/strokes, have a big power band and don't need so many gears.

Anyway you go, you need some kind of Gearbox to keep the engine RPM within it's power band, while providing the bike with a good acceleration, and speed range. While there are lots of styles and types of gear boxes, I think they all seem to boil down to three different crankcase types.

  1. Horizontally split...
    ...

    The crankcase has a seam on the horizontal plane. All multi cylinder I have seen are split Horizontally. This means you do not have to take the Cylinder Head off to replace a gear.

  2. Vertically split...
    ...

    The crankcase has a seam on the vertical plane. Most single cylinder engines are split vertically but not all of them. The Honda XR/XL175 comes to mind.

  3. Cassette type...
    ...

    The gears are loaded in from one side. Like a Cassette tape. Triumph, BSA, and Harley-Davidson Sportsters have used this style of Gearbox.

Back in the day, say before mid 1950s, the Gearboxes were separate from the engines on a lot of machines but now-a-days the engines and Gearboxes are all one unit.

Most all of the Gearboxes on motorcycles are 'constant mesh'. That means all the gears are constantly meshed with one another and are always spinning. Because of this, there are no synchros to speed up the gears when they engage, like there are in automotive Gearboxes.

In the motorcycle gearbox there are two shafts. In most of them, the one with the clutch on the end of it is the main shaft. The other is the countershaft and it has the countershaft sprocket on one end of it. A few have the clutch and counter sprocket on the same shaft. Some of the gears are fixed and/or machined to the transmission shafts. The other gears slide or spin on these shafts. The gears that slide back and forth on the shafts have what are called Dogs. These Dogs are knobs of metal that fit into holes in the gears beside them, locking the two gears together.

The sliding gears are moved back and forth by Shifter Forks which in turn are moved by a shifter drum.The Shifter Forks are usually attached to the Shifter Drum or move in a groove machined in the Shifter Drum. This drum is turned or rotated, through different styles of linkages, by the gear Shifter Shaft Linkage.


Shifter Drum

Shifter Drum with Grooves

Shifter Shaft Linkage

As the gears move back and forth they lock the main shaft and counter shaft together thru each set of gears, giving us 1st, 2nd, 3rd, etc. A few use a grooved plate to move the shift forks.
While the design of the Gearbox is complicated, fixing, repairing, or overhauling it really isn't. However, there are a few things to watch for.

Always put everything back in EXACTLY the same position as when you removed it. Many shafts or gears can go in backwards and work just fine, BUT you will have reversed the wear pattern, and the parts will have to re-wear themselves into each other. This increases the wear on your parts for no good reason. So if for nothing more than the general principal of the thing, always reinstall parts in the exact position they were in. If necessary mark them with a Marks-a-lot felt tip pen.

Atv gearbox with reverse

When you pull the gears out, DON'T just dump the gears out on the floor like a sack of potatoes. Pull them out gently, as a unit. On some it is best to pull both shafts, drum and the shift forks together. On others it's best to remove the shafts that hold the shifter forks and remove them first, then the drum, and then the gear clusters. On some makes the gears are kept on the shafts by circlips. On others, the gears can fall right off. Often there are shims ( thin, large washers ) on the ends of the shafts. These shims are used to position the gears and take up any side play, so look for them when you pull any shaft out. They tend to stick to the bearings. You may need to clean the part of the counter shaft that is outside the crankcase. You know, where the countershaft sprocket is. Get all that rust and dirt off it, so it will slide on out through the bearing.

When you disassemble the gear shafts, use a cardboard egg crate to hold the gear parts in the order that you disassemble them.

If the transmission wants to jump out of gear, usually second gear, under power, take a good look at both the Dogs and the holes they fit in and the sides of the Shifter Forks for wear. If there is any wear at all on these parts replace them.

If the gear has broken teeth it is a good idea to replace both it and its mate on the other gear shaft. Normally broken teeth make quite a bit of noise. Sometimes, there is a lot of noise, but when you get the gear out... nothing looks broken. Look for a bent tooth, or a tooth with a bit of debris stuck on it. It could be a bit of steel, aluminum, who knows what, it can still make noise.

When you inspect the gear teeth, you will notice that, on almost all them, there are a lot more pits and wear lines than what we would like to see. These gears are from a well worn Honda CR480. A powerful bike back in the day. On this example the crankcase around the main crank bearing broke. The gears, pits and all, were going strong.

All the books say replace them... but man... if I did that, I'd have to replace them all. That would cost a lot of cash. So it's a judgment call you will have to make. If they are really bad, replace them. Just be sure to take into account the cost of the gears verses the worth of the machine and its power output. Expensive, high power machines deserve and require good gears, but a $500 machine does not need $500 worth of new gears.

Gearbox Bearings are another judgment call. They run in an oil bath and rarely wear out. Even if the oil level is run low the gear box bearings probably get more oil than the average 2/stroke main bearing. As with gears if they look OK they Probably are. If it's a high power, expensive, machine...put in new. Cheapo machine? Just live with them.

Now, speaking of living with it...sometimes a Gearbox will loose a gear... bang, it's gone. Now, you can run through all the gears, everything sounds OK, but one of the gears is just not there anymore. Can you ignore it and just drive on? I think you can. Yes, there is always the risk that whatever broke could get jammed in other parts of the Gearbox, locking everything up and doing a lot of damage. Do you want to risk it? I think the odds are good that you will not have any problems, except your missing a gear. But understand, there is a RISK.

Motorcycle Transmission

OK, now you assemble the gear clusters and put them and everything else back in the crankcases, with lots of oil, of course. Now you try to shift through all the gears, and man, it shifts sort of hard. Did you do something wrong? Maybe not. If you were careful on assembly and the gear shafts turn easily, just make sure you can shift thru all the gears. It helps to spin the gear shafts by hand as you shift to help things slide into position. If it's just a bit hard, kind of chunky, so to speak, you are OK. When it's spinning fast, it will work just fine.

Yes, there are motorcycles with Automatic Transmissions. Honda had a 750cc and a 400cc, Suzuki had a 450cc, and Moto Guzzi had a 1000cc automatic. These were true automatics.

Most were made in the late 70's, early 80's and had a 2-speed gear box with a torque converter. I've ridden the Honda 750 and it was...well... automatic. With two speeds it was no ball-of-fire, but it was OK. You don't see them around much and as I have never worked on one, I probably shouldn't try to tell you how to fix one.

Rokon Had a 340cc dirt bike with a snowmobile type, belt drive, transmission with drive and driven clutches. Rokon also has a two wheel drive, backwoods, motorcycle with the same type of clutch. Works quilt well once you get used to it. It will go just about anywhere.