Technical Info

• Drive train or Power train
• Gear Ratio
• Chain Types: Size & Pitch
• Chain maintenance
• Replacement

An a vehicle, the term drive train or power train refers to the group of components that generate power and deliver it to the road surface, water, or air. This includes the engine, transmission, drive hafts, differentials, and the final drive (drive wheels, caterpillar track, propeller, etc.).

Sometimes "power train" is used to refer to simply the engine and transmission, including the other components only if they are integral to the transmission. (source: WikiPedia)

For a motorcycle the rear wheel is also part of the drive train as it delivers the power to the road. So the size of the rear tire also influences the drive train.

Gear Ratio

According to Wikipedia Gear Ratio is:
"The relationship between the number of teeth on two gears that are meshed or two sprockets connected with a common roller chain, or the circumferences of two pulleys connected with a drive belt."

But in a motorcycle the are more then one gear at work so there also are more gear ratio. All these are working together and form the overall ratio. Most gearing consists off:

• Primary drive, this is the gear ratio between engine RPM and the clutch shaft RPM, also called 'Primary reduction ratio'
• Gearbox ratio, this is the ratio between the clutch shaft RPM and the countershaft RPM.
  Because there are more gears in a gearbox, different ratio are possible
• Final drive ratio, this is the ratio between countershaft RPM and rear sprocket RPM
• The ratio between the Rear sprocket and the rear wheel (rear tire that is !)

Chain Size & Pitch

Below a table containing chain pitch and roller width (E) for most motorcycle chain types in mm and inch:

Proper chain maintenance is essential for safety, maximum performance and a long chain & sprocket life. The interval at which a chain needs maintenance depends on the type (sealed or not) and the way it is used and is mostly described in the User Manual. To be on the safe side, have a look at your chain after each ride and maintain it after every 500 km or about 300 miles. But like I said, these intervals differ per bike so check your manual !

Lubrication
Although most modern chains are sealed and pre-lubricated, the external of the chain (rollers and side blades) need to be lubricated (very) regularly. This will also keep the chain clean and corrosion free. Use the intervals mentioned above but when driving in wet or extremely dusty conditions, lubricate more often ! Also lubricate the chain while it is still 'hot', that is following a ride.

Cleaning
Although there are many products to clean a chain, Tsubaki recommends the use of a "moisture displacement lubricant" to clean chains and to not use any dissolvent, petrol, diesel, detergents, steam-cleaner or coarse brush because it will damage the chain. In fact it will damage the seals which will cause the chain to wear very fast.

How to Lubricate/Clean
To spread the lubricant over the chain, it must be rotated while lubricating. Therefore if you have a center stand use that, if not, get some help an tilt the bike on the jiffy so the rear wheel is off the floor.

Because using a spray always causes a 'cloud of lubricant' that will descend on your rim and  tire so maybe it is a good idea to protect them using an old newspaper or piece of cardboard. Try to aim the spray between the side blades and the rollers like illustrated below, first the left side. Spray and rotate the rear wheel at least 3 complete revolutions. Then do the same on the right side of the chain.

After spraying, you need to wipe off the excessive lubricant using a dry and clean cloth.

Adjusting chain tension
Both a to tight chain or a to loose chain will wear out faster or even cause danger so it is important to keep the chain at the right tension. This right tension will differ per motorcycle and is often described in the Owner Manual. Most common method for checking is placing the bike on the center stand when available or on a paddock stand or tilted on a jiffy and measure the slack of the chain in the middle like illustrated below.

Turn the rear wheel slowly until you find the position where chain is tightest. Push the chain up pressing with a finger at mid-length of swing arm. The lower stretch of chain must have a slack of about 25 mm 1". The exact slack depends on the type of chain and length of the swing arm and should be checked in your User manual. If not available, the example above is a good average.

Sprocket Alignment
To prevent noise and fast wear of the chain, the sprockets must be aligned in 2 direction:

When the chain tension needs to be adjusted, make sure that the rear sprocket is aligned with the front sprocket.
To adjust the tension and/or alignment:
Slacken the nut (1) of the wheel shaft, tighten (turn clockwise) or slacken the screw (2) on either side of the swing arm equally to increase or reduce chain tension. If you are slackening the chain, you will have to push the wheel forward. Make sure you have adjusted to the same setting marks (red) on both sides of the swing arm. Refer to the position of the slider (4) on both sides.

If there are no marks on your swing arm you can either create them your self or measure the distance of the slider to the end of the swing arm (green arrow) on both sides and make sure they are equal. This will ensure perfect wheel alignment and thus a perfect sprocket alignment. If the rear wheel and sprocket is not aligned with the front sprocket, both chain and sprockets will wear very fast.

Chain & Sprocket replacement

Does a chain really "stretch"? The term "stretch" is misleading. A chain will elongate when the pins and bushings wear down. This is due to poor lubrication, under sizing and overloading of the chain. As the components thin, the space between the pins and bushings increase, thus making the chain longer than originally. For transmission chain, there is almost no risk of fatigue failure when wear elongation is less than or equal to 1.5 percent.

A direct measure of chain wear is the extension in excess of the nominal length of the chain. Lay the chain on a flat surface and, after anchoring it at one end, attach to the other end a turnbuckle and a spring balance suitably anchored. Apply some tension load by means of the turnbuckle.

Of course this is more easy with a 'broken' chain that has 2 ends but is is also possible with an endless chain, just measure part of the chain and count the # of measured links (as many as possible):

Measure length ‘M’  in millimeters from which the percentage extension can be obtained from the following formula:

                                     M - (X * P)
Percentage extension =    -------------         Where X = # of pitches measured, P = pitch (in mm for more accuracy)
                                    (X * P * 100)

As a general rule, the useful life of the chain is terminated and the chain should be replaced when the percentage extension reaches 2 per cent.

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