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Chain Drive Mechanism - The Basics
As mentioned earlier, chain drive systems transfer mechanical energy from the gearbox to the rear wheel. The power is transmitted over a roller chain known as a drive chain or transmission chain that sits over sprockets. The chain is made up of short cylindrical rollers of a specific diameter and held together by chainplates on both sides of the roller. The rollers are equally spaced out to mesh with the teeth of the sprockets. Sprockets are metal discs and, like gears, have teeth along their circumference.
The drive chain mechanism needs two sprockets and a drive chain to function. A smaller sprocket is connected to the gearbox and a larger one is present on the rear wheel. The gearbox turns the front sprocket which, with the help of the chain drive, turns the rear wheel, putting the motorcycle in motion.
There are different types of drive chain options available. While the low-cost, commuter-oriented motorcycles often utilise standard roller chains, higher capacity bikes generally use either O-ring or X-ring chains. These ring chains use rubber rings that act as small seals between the inner and outer plates of the chain assembly. These rings or seals keep grease locked in the pins and bushings; while also keeping the dirt out, allowing the links to run smoothly, preventing them from jamming up and enhancing their life. Let’s have a look at how these chain types work and what are their advantages and disadvantages.
Standard Roller Chains
To understand the mechanism of a standard chain drive, we need to know the components of a chain drive system first. A standard roller chain for a motorcycle consists of several parts. In essence, it is metal links connected in a series as outer and inner links. These links are formed by smaller components, including outer plates for the outer links and inner plates for the inner links. Between these plates, at the centre, you have solid pins, which are surrounded by bushings, or hollow pins. On top of these bushings, you have cylindrical rollers which roll over the teeth on sprockets to allow for a smooth, relatively friction-free transmission of power.
As you would imagine, an efficient movement of these metallic links, or chain, as we call it, would depend on proper lubrication between the pins and bushing, and smooth movement of the rollers as well. The standard roller chains don’t have a mechanism to seal any grease or lubrication between the pins and bushings. The inner and outer links in these chains are not sealed, which means that the moving components are prone to attract muck, grime and other unwelcome materials. This often leads to the standard roller chains not operating fluidly, getting jammed, rusting and causing the sprockets to wear early. Since they are vulnerable to the elements, the non-O-ring chains have to be protected with a chain cover, which restricts access. Standard roller chains also rust easily, and require frequent cleaning, making it relatively tedious to maintain them.
Here’s a quick look at the pros and cons of the standard, non-O-ring roller chain:
Pros:
● Simple design and structure
● Low manufacturing cost
● Lightweight
● Chain cover protects the chain from muck and dust
● Lower drag and marginally better power transmission
Cons:
● Difficult to maintain and clean as they are covered in a case
● Loosens frequently
● Makes the sprockets wear off faster
● Needs frequent lubrication
● Doesn’t last very long
O-Ring Chains
An O-ring chain is quite similar in construction to the standard roller chain, except for one key difference - it has an arrangement to seal in lubrication between the links. O-rings are nothing but rubber rings with an O-shaped cross-section, placed between the outer link and inner link plates around the pin bushings to seal the lubrication. The chain manufacturer in this case pre-fills the space between pins and bushings with grease for lubrication, which, in turn, is sealed by the O-ring. In addition to forming a barrier that holds the lubricating grease inside the pin and bushing wear areas, the seal also prevents dirt and other contaminants from entering the chain linkages. The O-ring chains, thus, have a much longer life compared to standard roller chains, and they also don’t require lubrication for the most part.
A downside of O-ring chains is that the addition of rubber rings increases friction in the movement of the chain, creating more drag and fractionally reducing the power delivered to the rear wheel. While there is a very marginal reduction in the power transmitted to the rear wheel in the case of O-ring chains, the advantages they offer over standard chains far outweigh this minor shortcoming.
The pros and cons of O-ring roller chains are listed below:
Pros:
● Don’t require lubrication for the large part
● Easy to maintain
● Easy to clean as there is no case or cover
● Perform better at higher speeds
● Last longer
● Don’t require frequent tightening
● Make less noise
● Sprockets last longer
Cons:
● Cost is higher than standard roller chains
● Higher resistance, resulting in drag
● Requires special lubricating agents, if ever the need arises
X-Ring Chains
The X-Ring chains were designed to overcome the relatively higher resistance and drag O-ring chains create as compared to the standard roller chains. As the name X-ring suggests, the rubber seals between the inner and outer links on the X-ring chain have an X-shaped cross-section as opposed to the O-shaped cross-section of the O-ring chains.
So how exactly does an X-shaped cross-section of the ring reduce friction and drag? The most significant factor at play here is the surface area. When compressed between the plates, the O-ring creates a large surface area, which increases friction and therefore, reduces the power transmitted to the rear wheel marginally. As opposed to the large surface area created by a compressed O-Ring, the X-cross section offers two smaller surface areas with lesser friction and wear, thus significantly reducing drag. X-ring is also known to provide better sealing than O-ring and therefore does a better job of packing the grease in. X-ring chains are also known to last longer than their O-ring counterparts.
The advantages and disadvantages of X-Ring chains are listed below:
Pros:
● Don’t require lubrication
● Easy to maintain
● Easy to clean as there is no case or cover
● Perform better at both high and low speeds
● Last really long
● Make less noise
● Sprockets last longer
Cons:
● Most expensive among all other chain options
● Requires special lubricating agents, if ever the need arises