Adjusting Motorcycle Cables
Some of the simpler mechanicing jobs on a motorcycle include changing a spark plug, adjusting a chain and, in this example, adjusting the control cables.
Although the actual job of adjusting cables is simple enough, there are safety issues associated with it. The author has placed an asterisk (*) at the point where safety is an issue.
A typical set of control cables for a motorcycle includes the front brake cable, throttle cable, clutch cable and, in some cases, a rear brake cable.
(*) Adjusting the front brake cable is simply a case of setting the free play; that is, the amount of play in the lever before the front begins to operate or slow the bike down. However, the amount of retardation offered by the various bikes, brake designs, and climatic conditions will greatly affect the efficiency of a brake. In addition, a certain amount of personal preference will come into play here too.
First and foremost, the front brake plate should be centralized within the brake drum. To achieve this centralization the mechanic should place the bike on its center stand. The front spindle retaining nut should then be backed off (loosened).The mechanic should then get an assistant to press down on the seat, which will have the effect of lifting the front wheel off the ground. The wheel should spin freely at this stage. The front brake lever should now be pulled in until the wheel stops spinning. Holding the lever at this position, the mechanic must now re-tighten the front wheel spindle nut—setting the tightness to the correct torque value.The brake plate will now be centralized inside the brake drum.
With the brake plate centralized, the cable free play can be set. Ideally the maximum amount of brake pressure should be evident when the rider's fingers are at 90 degrees at the first knuckle. Settings to avoided include too much play where the lever comes back to the handle bars at maximum braking, or when the rider has to stretch to reach the lever. (Note: Most manufacturers recommend setting the free play at around 1/8" or 3-mm between the lever and the pivot at the cable end.) After the cable has been set, the mechanic must check that the wheel is not binding by spinning the wheel (if there is a small amount of binding, the mechanic may need to recentralize the hub again).
A throttle cable on a motorcycle connects the handlebar twist grip to the carburetor slide. (*) To ensure the carburetor closes fully, it is necessary to have a small amount of play at the twist grip before the slide begins to lift. When the rider opens the throttle, he or she will feel a slight resistance as the slide begins to rise; this is due to the slide's return spring becoming compressed.However, the mechanic must allow for any idle adjustment at the carburetor as this will falsify the point of lift. To achieve accurate results, the mechanic must remove the air filter and back off the idle adjusting screw until the slide is fully closed before setting the free play in the cable.
Typically, most riders prefer a small amount of free play in the cable, however, as mentioned above, the free play will be affected by the idle screw position. For example, if the free play is set at 1/16" with the idle screw fully disengaged from the slide, there may be as much as 1/8" of play when the idle screw is positioned to give the desired idle. (Note: This is an extreme case and not typical; nonetheless, the effects of the idle screw must be born in mind.)
(*) Having made any changes to the throttle cable, it is imperative to check the free play throughout the entire travel of the handlebars—from lock to lock. To do this, the rider should ensure the throttle closes in all positions of the handlebars. A typical problem here is when the cable goes tight at, or near to, full lock. This is a very dangerous situation and must be corrected before riding the bike.
The clutch cable disengages the engine from the rear wheel when the bike is in gear. If the cable has too much free play the gears will crunch when the gear lever is moved or (*) the machine will move forward as the gear is selected (A small amount of crunching or movement is normal, especially when cold).
Before setting the clutch cable free play it is necessary to set the clearance on the clutch push rod or operating arm. Different designs require different amounts of free play on the push rod; therefore, the mechanic must check the shop manual for the particular bike being worked on. In the absence of a manual, a half or full turn out on the adjusting screw will ensure the push rod or operating arm is not riding on the clutch push rod.
After the adjusting screw has been checked/set, the cable can be adjusted to give approximately 1/8" or 3-mm of free play at the lever.
Cable operated rear brakes are not common; setting their free play follows most of the information applied to the front brake cable. However, the brake lever position must be set first. Most rear brake levers have an adjustable stop that restricts the amount of vertical movement of the lever. The mechanic should aim to set the lever so that it is centralized on the rider's foot in the normal riding position. This position will require the rider to lift his or her foot slightly to depress the brake lever, but will position the foot correctly as the brake begins to slow the bike.(*) The amount of vertical down movement required to operate the brake is adjustable via the cable and to a certain extent is down to the rider's preference. A long lever travel before the brake begins to apply should, however, be avoided.
Although the actual job of adjusting cables is simple enough, there are safety issues associated with it. The author has placed an asterisk (*) at the point where safety is an issue.
A typical set of control cables for a motorcycle includes the front brake cable, throttle cable, clutch cable and, in some cases, a rear brake cable.
1. Front Brake Cable
(*) Adjusting the front brake cable is simply a case of setting the free play; that is, the amount of play in the lever before the front begins to operate or slow the bike down. However, the amount of retardation offered by the various bikes, brake designs, and climatic conditions will greatly affect the efficiency of a brake. In addition, a certain amount of personal preference will come into play here too.
First and foremost, the front brake plate should be centralized within the brake drum. To achieve this centralization the mechanic should place the bike on its center stand. The front spindle retaining nut should then be backed off (loosened).The mechanic should then get an assistant to press down on the seat, which will have the effect of lifting the front wheel off the ground. The wheel should spin freely at this stage. The front brake lever should now be pulled in until the wheel stops spinning. Holding the lever at this position, the mechanic must now re-tighten the front wheel spindle nut—setting the tightness to the correct torque value.The brake plate will now be centralized inside the brake drum.
With the brake plate centralized, the cable free play can be set. Ideally the maximum amount of brake pressure should be evident when the rider's fingers are at 90 degrees at the first knuckle. Settings to avoided include too much play where the lever comes back to the handle bars at maximum braking, or when the rider has to stretch to reach the lever. (Note: Most manufacturers recommend setting the free play at around 1/8" or 3-mm between the lever and the pivot at the cable end.) After the cable has been set, the mechanic must check that the wheel is not binding by spinning the wheel (if there is a small amount of binding, the mechanic may need to recentralize the hub again).
2. Throttle Cable
A throttle cable on a motorcycle connects the handlebar twist grip to the carburetor slide. (*) To ensure the carburetor closes fully, it is necessary to have a small amount of play at the twist grip before the slide begins to lift. When the rider opens the throttle, he or she will feel a slight resistance as the slide begins to rise; this is due to the slide's return spring becoming compressed.However, the mechanic must allow for any idle adjustment at the carburetor as this will falsify the point of lift. To achieve accurate results, the mechanic must remove the air filter and back off the idle adjusting screw until the slide is fully closed before setting the free play in the cable.
Typically, most riders prefer a small amount of free play in the cable, however, as mentioned above, the free play will be affected by the idle screw position. For example, if the free play is set at 1/16" with the idle screw fully disengaged from the slide, there may be as much as 1/8" of play when the idle screw is positioned to give the desired idle. (Note: This is an extreme case and not typical; nonetheless, the effects of the idle screw must be born in mind.)
(*) Having made any changes to the throttle cable, it is imperative to check the free play throughout the entire travel of the handlebars—from lock to lock. To do this, the rider should ensure the throttle closes in all positions of the handlebars. A typical problem here is when the cable goes tight at, or near to, full lock. This is a very dangerous situation and must be corrected before riding the bike.
3. Clutch cable
The clutch cable disengages the engine from the rear wheel when the bike is in gear. If the cable has too much free play the gears will crunch when the gear lever is moved or (*) the machine will move forward as the gear is selected (A small amount of crunching or movement is normal, especially when cold).
Before setting the clutch cable free play it is necessary to set the clearance on the clutch push rod or operating arm. Different designs require different amounts of free play on the push rod; therefore, the mechanic must check the shop manual for the particular bike being worked on. In the absence of a manual, a half or full turn out on the adjusting screw will ensure the push rod or operating arm is not riding on the clutch push rod.
After the adjusting screw has been checked/set, the cable can be adjusted to give approximately 1/8" or 3-mm of free play at the lever.
4. Rear Brake Adjusters
Cable operated rear brakes are not common; setting their free play follows most of the information applied to the front brake cable. However, the brake lever position must be set first. Most rear brake levers have an adjustable stop that restricts the amount of vertical movement of the lever. The mechanic should aim to set the lever so that it is centralized on the rider's foot in the normal riding position. This position will require the rider to lift his or her foot slightly to depress the brake lever, but will position the foot correctly as the brake begins to slow the bike.(*) The amount of vertical down movement required to operate the brake is adjustable via the cable and to a certain extent is down to the rider's preference. A long lever travel before the brake begins to apply should, however, be avoided.
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