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Whether you've been riding motorcycles for a while or you are interested in getting one, knowing how your bike works, and basic mechanics, is essential. Following on our "Guide to parts of a motorcycle and their functions", we will be looking at each of the parts and components in a bit more detail.

One key component of your bike that you will be using a lot while riding is the motorcycle's transmission. Most people understand that this is a crucial part of their bike, but not exactly what it is. We will be looking at answering most common questions, such as how does a motorcycle transmission work, the difference between the gears and transmission, the issues you can experience with transmission and how to maintain one. So let's dive in.


What is a motorcycle transmission?

The transmission is one of the essential components of any vehicle, whether it is a car or a motorcycle. Usually it is compact, lightweight and manageable. The transmission offers a few purposes for the vehicle it is in. These are:

● It ensures that the engine speed is in the suitable range according to the vehicle's speed.

● It allows the engine to work separately from the wheels when the vehicle is not moving.

● It transfers the torque from the vehicle's engine to the rear wheel.

● It allows the driver to control the speed.

In essence, motorcycle transmissions allow the engine's RPM to stay optimal, enable the vehicle to accelerate from rest, and remain at cruise speed. The transmission contains a range of gear ratios that can be selected to provide optimal torque and engine speed. Without a transmission, the engine speed would be too high or too low, which is not optimal for its power and efficiency.


Motorcycle transmissions designs

Knowing the design of your bike and the location of the transmission will help you maintain your motorcycle. Furthermore, it will help you understand any potential problems and how to fix them.

Unit Construction

The one unit construction in very common construction type, especially for the Japanese bikes and Italian models. In this design, the engine and gearbox components are in a single housing.

Non-unit Construction

As the name suggests, the non-unit construction means that both the engine and the gearbox are kept separate, with the engine usually sitting in front of the gearbox.


Types of motorcycle transmission

Manual transmissions

Manual transmission in motorcycles means that the rider has to manually select the correct gear by operating the clutch lever on the handlebars and gear shifter pedal.

Most motorcycles have manual transmissions with sequential gearbox and either five or six gears. Sequential transmission is a non-synchronous transmission used on light vehicles such as motorcycles, the majority of quad bikes, go-carts, mowers, microcars and racing cars.

The sequential manual transmission restricts the rider to select only the neighbouring gear. Going either one gear up or one gear down in successive order. This restriction avoids accidentally selecting the wrong gear and prevents from deliberately "skipping" gears. On the positive side, it allows faster shift times.


Automatic transmissions

A multi-speed automatic transmission means that the driver doesn't need to change or select any gears while driving. There is no shift pedal, no neutral, no push or pull required by the foot. Just twist the throttle and you are set to go... The gears are automatically adjusted to optimise the RPM of the engine in relations to the speed of the vehicle.

Fully automatic transmission is used by many smaller vehicles such as scooters, mopeds, mini-bikes and some custom cruisers. There are several types of automatic motorcycle transmission.

  • Continuously variable transmission - Most common on mopeds and scooters; it was introduced into motorcycle industry by Honda in 1973. This particular design has three parts to the transmission. There are two conical pulleys, a centrifugal clutch and a belt. As the engine RPM changes, the centrifugal clutch pushes the belt along the conical tapered pulleys, resulting in smooth acceleration.

  • Dual clutch transmission - As the name suggest, there are two separate clutches, one for odd gears and one for the even ones. The DCT is usually used by four wheelers such as cars and trucks. The first motorcycle using this kind of clutch was the 2009 Honda VFR1200F.

  • Hydraulic transmission

  • Transmission on electric motorcycles - electric motors don't need manual gear changes, so their clutch can be considered as a type of automatic transmission.

Semi-automatic motorcycle transmissions

The semi-automatic transmission is mechanically based on sequential manual transmissions. The clutch is usually centrifugal, so there is no need for clutch lever, however the gears still need to be manually selected using the conventional heel-and-toe foot shift lever.


How does a motorcycle transmission work?

To understand how the motorcycle transmission works in classical bikes, you must first understand the clutch and its function. The clutch acts as the negotiator between the transmission and the engine. When you output the engine power, the clutch allows it to enter the main transmission shaft before reaching the rear wheel.

Motorcycle transmissions have gears arranged in a specific sequence on the shafts. That means that the driver will have to go through each of them in order. The layout is usually 1-N-2-3-4-5-6. Which means that the neutral gear is found "half click" away from the first or the second gear.


There are two shafts within the transmission: the input shaft and the output shaft. The output shaft is connected to the bike's rear wheel, while the input shaft connects to the engine. These shafts have various gears connected to them, including some that lock onto other gears. The foot pedal shifter controls this locking mechanism within the transmission. Depending on the motorcycle's gear, the gears within will spin accordingly and provide the appropriate engine power to the wheel.


Common classic motorcycle transmission issues

In-operational Shift Lever

The shift lever turns the shift drum when you are selecting the gear. A spring is used to hold the selection, which can get worn down with repeated use. Eventually, this can result in the lever not returning, which can cause the shift lever to stop working. Lubricating can help fix this issue, but you will have to replace the shift lever or the spring if the damage is too severe.

Clutch Failure

As mentioned above, majority of classical motorcycles have manual transmissions, which means that the clutch plays a crucial role. As a result, the clutch can get worn out, resulting in them failing to work. Some signs of a failing clutch include delay in acceleration, difficulty in shifting gears and clunky noises. You will have to get your clutch readjusted or replaced in such a case.

When rebuilding classic motorcycle clutch, look out for the correct set up of the clutch plates as per owner's manual. Also over time, clutch plates can become worn out (either too thin or too thick), the clutch plates can get mishapen, or grease might get into the clutch basket rotting the clutch rubber dampers within.

Clash of gears

Gears can clash when the space between their teeth gets widened from repeated use. This can cause them to collide with each other when the clutch is used, resulting in a clunking sound. Older motorcycles especially are more prone to this problem. This is a highly complex issue to fix that may require rebuilding or replacing the transmission itself.

When rebuilding the transmission assembly, a particular care should be given to checking every gear coggle and teeth on it for cracks, chipps and rounding off. Any damaged wheels should be replaced.


How to rebuild the motorcycle transmission?

Rebuilding a motorcycle transmission is not something a novice should embark upon. However with the correct set of skills, your motorcycle's manual at hand and bit of hard work, you might be able to fix the issue.

If you are inexperienced with motorcycle repairs, or you are not sure if the issue is with the clutch or the transmission, you might want to entrust the repair to an expert such as My Transmission Experts, who gave us the following tips, should you give it a go yourself.

Some of the steps mentioned below can vary between models, so consult your owner's manual if in doubt.

●       Remove the engine out of your motorcycle

●       Split or open the cases

●       Turn the clutch release lever until the cover comes off

●       Take a picture of everything to ensure everything gets reassembled properly later on

●       Remove the clutch bolts, disks, nuts etc.

●       Remove the stator cover

●       Flip the engine over, separate the cases and remove the shift mechanisms

●       Lift the drive shafts out and remove all the gears one by one

●       Lay the gears out in order

●       Clean and replace them according to your needs

●       Reassemble all the components using the picture you took as a comparison.


How to service the motorcycle transmission?

There are many transmission maintenance services that your motorcycle can benefit from. This will ensure that the transmission is working smoothly and prevent the aforementioned issues. Some of these include:

●       Changing the engine oil. This is particularly important if you have a single unit transmission, where the engine is contained in the same housing. You must use the correct type of oil and ensure there aren't any lumps or shavings in it, as this can create future problems for the transmission assembly.

●       Replacing the transmission fluid. Many motorcycle owners believ that a transmission oil is identical to the engine oil. However that is not always the case. If you transmission is separate from the engine, you are most like to require a special fluid to lubricate the transmission mechanism. Always, ensure that you use the correct one as manual and automatic transmission fluids vary in their viscosity levels.

●       When restoring a classic motorcycle, you should take extra care rebuilding the transmission. Cleaning and replacing all the faulty and damaged transmission components as well as servicing the clutch assembly will ensure that your bike is a pleasure to ride for years to come.

●       If all fails, taking your motorcycle to an expert who can check for any missed repairs, might be your best bet.

Conclusion

The motorcycle transmission plays crutial part in the functioning of both, classic and modern motorcycles. It allows you, as a rider, to control the speed of the bike, the performance of the engine and in the end, the fuel efficiency as well.

We have discussed the different types of transmision as well as the mechanisms of the clutch and the gears. Additionally, we have looked at various transmission issues and how to deal with them. We have also looked at the basics on how you can rebuild your transmission and on the basic maintenance.

Hope you found this article useful.

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