If the “Joint Coupling” is Able to be Inserted to Drive Part of the Speedometer Gear

20210922_000.jpg How to

Most modern models use an electric speedometer, which replaces the number of revolutions of the wheel with an electrical signal to drive the speedometer. A typical mechanical speedometer is a speedometer that is driven by a gear built into the wheel hub. Starting in the late 80's, Honda's racer replica models began using a drive system that rotates the meter cable by installing a "joint or coupling" over the center nut that tightens the drive sprocket.

In this article, I will focus on the "extraction" of the speedometer gear for such type of models. Let's practice disassembly maintenance.

Gear on the extension of the coaxial core of the drive sprocket


In modern world, it is summed up by the super sports model, but in the 80's, there were racer replicas, and then models called "real racer replicas" after the movement heated up. At that time, there were many models that had eliminated the meter cable drive for one purpose of simplicity around the front wheel, with the meter cable along the fixed side = body side and the speedometer gear taken out of the drive sprocket's rotating shaft. This was the case, for example, with the VFR/RC/NC/NSR series.

Plastic coupling to drive the cable


The speedometer gear is built into the drive sprocket cover, and is set into the head of the center bolt that secures the drive sprocket via a plastic part that serves as a "coupling" between the two on the inside of the cover. The mechanism is a bolt head that synchronizes with the rotation of the drive sprocket to rotate the meter gear.

New parts are fixed with a low-pressure fit.


Although it depends on the condition of the motorcycle, the coupling of the meter gear for RVF400R that I disassembled this time had a rattle and could be easily pulled out with my fingertips, whereas it should be a low pressure fit. The rotation of the shaft must have caused the press fit to become loose. Some of the motorcycles that had been ridden in had further rattled and destroyed this coupling. After cleaning around the gears, new parts (parts were still being supplied at the time of this shooting) were press-fitted. At this point, a vise was used to press-fit and fix the parts so as not to push in too far.

Applied some buffer grease to the contact area.


Grease is applied to the contact area between metal and plastic parts to act as a buffer. Since it is a plastic and metal part, I used rubber grease to avoid affecting the plastic part. I want to avoid getting chain grease and other contaminants on it, but since it is in the center of the drive sprocket, it seems unlikely that centrifugal force will cause chain grease to fly off and stick to it. It is important to clean the parts when the sprocket cover is removed.

Checking the operation of the meter gear


After fixing the coupling parts, try to rotate it with your fingertips to make sure the shaft that drives the meter cable is rotating. The internal gears are not sold separately, so if the gears are too dirty, clean the parts and use a grease sprayer with an ultra-fine nozzle to seal the grease without damaging the seals.

RVF, a model representing the best era of motorcycles


The unprecedented motorcycle boom that began in the early 1980s gave birth to numerous new models. In the late 80's, when the popularity of racing was particularly high, models that looked like production racers with only security parts installed appeared. Honda has a lineup of models in the mid-sized motorcycle class that boast intense performance. The 2-stroke NSR series evolved year by year, while the 4-stroke CBR series with its parallel 4-cylinder engine was enhanced, and the VFR/RVF series with its V-4 engine was also a model that fostered many sport riders. The model that I took maintenance photos of was the Honda RVF400R, which was the final racer replica of the V-cylinder 400cc model that was introduced in the early 90s. This model has a unique exhaust sound characteristic of Honda V4.

  • Point 1: Clean the surrounding parts when disassembling parts, e.g., when removing various covers.
  • Point 2: Keep 3 types of grease on hand for sudden maintenance: MP (multi-purpose) grease, rubber grease, and molybdenum disulfide grease.

Many of the motorcycle instruments = meters are driven by a wire cable system. Nowadays, there are many electric meters that use electric signals to operate the meter, but electric meters started to be adopted in the early 1980s. At the time, the use of an electric speedometer as well as an electric tachometer was considered to be advanced, but there were still many problems due to the transitional stage of the technology. Most of these models were not adopted continuously and ended up being short-lived. One of the models that used an electric speedometer was the Kawasaki KZ1000R1.

The engineers wanted to do something about the presence of the meter gear, which was a hindrance to steering operation and also provided resistance to rotation. Some overseas motorcycles (British motorcycles) have had the speedometer driven out of the rear wheel hub since before the 70's. This is also said to be the result of the pursuit of lightness in steering operation.

It was Honda's racer replica models that hid the presence of such speedometer gears and cables from the front wheels. Due to the 1983 revision of the Vehicle Law, which approved models with full cowls, a new problem arose where the speedometer cable tended to interfere with the under cowl when it was driven by the front wheel. What was developed was a system that had a drive sprocket with a speedometer drive gear.

Many modern sport motorcycles have models that get an electrical signal from the rotation of the rear wheel to drive the speedometer. As you can see, various technological advancements are hidden in the parts of motorcycles that we normally don't pay attention to. The style of riding by straddling between the two front and rear tires and operating the handlebars has not changed in any way for more than a hundred years since the introduction of the motorcycle. However, with various technological advancements, the latest motorcycles of the world today are able to provide a stable and secure ride.

The focus here is on the speedometer drive gear area, which has been used in Honda's sports motorcycles since the late 80s. When the sprocket cover is removed, not only should the sprocket, drive chain, and inside of the case be cleaned and inspected, but the area around the meter gear should also be checked and inspected, and parts should be replaced as necessary. In particular, it is important to check the condition of the coupling parts (known as speedometer joints) that transmit the drive rotation power to the meter gear, and to secure spare parts before the parts become unusable.

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