How to determine if a sprocket replacement is needed
On forums, among saw owners, the question often arises “When is a sprocket replacement necessary and how to determine this?”. Replacement is done in two cases:
To reduce the risk of chipping, the guidebook specifies a tolerance for sprocket dimensions of 0.5 mm. If this indicator is exceeded, the chainsaw will vibrate noticeably, and this will affect the condition of the crankshaft bearings and the entire tool as a whole.
Experts say a sprocket lasts twice as long as a single chain. But in fact, owners often replace the sprocket only after 2-3 chain changes, in fact until the cutting edges are completely worn out. As a consequence, it comes to buy a repair kit and make a complete replacement of parts.
The wish of the owner to equip the set with the saw chain of different pitch leads to the necessity of changing the sprocket to the part with the corresponding profile ring. This requirement applies to the entire range of chainsaws made in Europe and China.
The operational reliability of the European-made chainsaw, when working in the severe conditions of high loads, may be considerably impaired if a sprocket made in China is replaced with a brand-name sprocket.
Algorithm of independent replacement of the clutch drum with a sprocket
The technology of replacement of the drive sprocket provides for the performance of the entire amount of work in a given sequence:
- The removal of the headset and air filter;
- Install a piston retainer in the spark plug hole;
- the clutch clutch and the gear train are removed with a puller and the sprocket can only be unscrewed in a clockwise direction.
If you find a lot of wear on the cage, breakage of the centrifugal mechanism springs and cams, it is recommended to replace the entire set.
If there is no doubt about the condition of the dismantled parts, reassemble the complete machine in the reverse order. For a reliable fixation of the clutch on the crankshaft it is enough to unscrew the piston lock, pull the cord of the regular starter and return it to its original position.
It is necessary to warn amateur masters from simplification of requirements of repair technologies and money saving on installation of rather cheap Chinese accessories.
the quality of the work done is guaranteed by attention, accuracy, observance of the sequence of all disassembly and assembly operations.
Replace the sprocket on the chainsaw can not only in the service, but also with their own hands. The whole process is relatively simple, the repair will require:
- spark plug wrench;
- a wrench to remove the clutch (an ordinary bolt wrench for a nut will do, but it is desirable that it be thicker);
- piston stopper (a special tool, but you can replace it with a tight cord);
- adjustable wrench / wrench (may not be needed).
Replacement of the drive sprocket and chain begins with fixing the piston in the chainsaw cylinder. To do this, remove the upper housing cover, air filter, and unscrew the spark plug. A special piston stopper is installed in this hole, but it is not in great demand among craftsmen: a metal one can scratch the piston, and a plastic one can break and get inside. Most often it is replaced by a normal thick cord or wire about 10. 15 cm long. It is important to keep it free of debris and metal wiring that could enter the cylinder.
Put a stopper or cord in the hole. The piston may be in the way, in order to lower it, you will need to slightly turn the sprocket by moving the chain or the chain itself in a clockwise direction.
Remove the cover on the side of the chain saw where the bar is fastened. It is usually held on by two bolts and clamped by two nuts. They can be unscrewed manually or with a wrench or universal wrench. Loosen the chain tension in order to remove the chain and guide bar. At this point you should also clean externally from accumulated dust, sawdust.
Replacing the chain sprocket on a Stihl chainsaw
Depending on the chainsaw’s design, the chain sprocket may be located under the clutch drum (either separately or as part of it), or on top of the. In the second case, everything is simpler. remove the part and replace it with a new one.
How to change the gas chainsaw clutch and drive sprocket
In other circumstances the assembly must be disassembled. The clutch has a left-hand thread, so unscrew it clockwise with a special or wrench, remove the drum, and then the sprocket can be removed. If the chainsaw has been in use for a long time, parts can become very stuck. In such a situation you will need to use physical force, but never use a hammer or chisel. this will destroy the entire part.
Remove all parts:
Perform an initial inspection of all components for wear and deformation. Then you can proceed to repair and take on the replacement of the sprocket on the chainsaw. If it is part of the clutch drum. the entire part must be replaced. An important point will be the selection of the new part. it must be similar to the original.
Design features and functions
The chain drive sprocket is functionally combined with the clutch drum that has spring loaded cams inside. The peculiarity of the construction device is that the motor shaft passes and freely rotates inside the clutch drum. The expander cams are rigidly fixed on the end of the shaft.
The spring compresses the cams when idling so they do not touch the drum. With higher rpm, the centrifugal force exceeds the spring rate and the cams come into contact with the drum walls. The latter starts to rotate.
The teeth of the saw chain mesh with the teeth of the drive sprocket. One of the functions of the automatic centrifugal clutch is to protect the engine when the load on the chain exceeds the allowable limit. This can occur if the chain jams.
The outside of the drum is covered with an emergency brake strap. When the handle is folded back, the belt is pressed against the drum and brakes the rotation. The effect is the same as for a jammed chain.
A special feature in all chainsaws is that the clutch drum and cams are attached to the shaft with a nut with a left-hand thread to prevent the mechanism from unscrewing during operation.
Replace Worn Parts
If the sprocket has an interchangeable ring gear, the condition of the base plate should be checked carefully. If you find dents, chips, deep scratches, changes in geometry or corrosion, replace not only the ring gear, but also the entire part. Worn and new parts working together in one assembly will shorten the life of the entire assembly. The risk of the chain jamming or breakage increases substantially.
In addition, there will be an increased vibration load on the clutch, transmission, and engine of the unit. The same factors apply if you use the same chain over a long period of time.
Folk “craftsmen” sometimes resuscitate stretched chain, simply throwing out one or two links and re-pressing the axle. In this case, the chainsaw needs to replace the sprocket.
The diameter of the gears (and therefore the number of teeth) should not be changed. Operating a larger or smaller sprocket produces forces in the transmission and engine that the designers of the unit did not anticipate. This will shorten the life of the tool and will not increase productivity.
Despite the presence in the chainsaw design of safety systems that instantly stop the movement of the blade if it breaks or the tire breaks and protects from flying torn links, it is better not to lead to such situations. The need to replace the pinion is only strengthened by the safety requirements.
Unit clutch design
Chainsaws are units that are equipped with drive sprockets, which are a single unit with a clutch basket.
The clutch operates automatically depending on the number of engine revolutions.
The units are fitted with a centrifugal type clutch, which is triggered automatically, depending on the number of engine revolutions.
When the machine’s engine is running at idle or low speed, the friction lining elements of the clutch have a certain amount of freedom in the radial direction. The freedom of movement causes the elements to be drawn to the center of the rotary shaft under the action of the springs, and does not transmit rotary motion to the sprocket drum. When the engine speed increases the centrifugal force exceeds the force of the springs, resulting in the displacement of elements with friction pads. These parts are pressed against the inner walls of the drum by centrifugal force. Through this contact, rotational motion is transmitted to the drum and sprocket, which drives the saw chain of the tool. The chainsaw sprocket can be located either outside the tool or under a special cover that protects the mechanism from damage and the device operator from injury.
The main advantage of this type of clutch is that when the saw chain jams, the elements with friction pads slip through, preventing serious damage to the combustion engine.
How to remove and change the sprocket on a chainsaw
Before you remove and replace the chain saw chainwheel sprocket, you must be sure that the part is no longer serviceable. To do this, you need to inspect the part, and a photo of a new and worn chainsaw sprocket is shown in the photo below.
The one on the left is new and the one on the right shows definite signs of wear. If after removing the tool guard a chipped tooth of the pinion is found, the part should be replaced. To do this you need to buy a sprocket in a tool store or in an online store, where the choice is much greater, which will allow you to choose the best option.
To change gears, you need to decide what kind of device is on the tool and what will be installed. The sequence of operations will be different for each type of mechanism. Replacement of the sprocket on a chainsaw of the first variant of the non-disassembled type looks as follows:
In reverse order the process of assembling the mechanism is carried out. If it is necessary to replace a collapsible-type product, the process is much the same, but in the end, one gear is replaced without the drum.
HOW-TO Replace A Chainsaw Chain Sprocket
If the replacement process has been completed, it must be checked. Check the strength of the chain, which includes a handbrake, and pulls the chain in the direction of its movement. The immobility of the product indicates that the mount is overtightened. You will need to loosen the tensioner to loosen it.
When replacement is needed?
The saw headset and drive sprocket are subject to natural wear and tear when in use. It is not a breakdown, but a routine maintenance procedure for the tool. Causes requiring sprocket replacement:
- Intensive and prolonged use of the saw;
- mechanical shocks to the headset;
- Using the wrong chain. Figure 2. Drive sprocket on chainsaw
Normal sprocket tooth wear is up to 0.5 mm. With regular use, it can be up to 1mm, but over time it will stress the engine and damage other parts of the saw. You can determine the need for replacement or repair by following the signs:
- There is mechanical damage on the guide sprocket;
- The width of the teeth is disproportionate to their height;
- there are asymmetrical angles;
- There are chipping, gouges, or large burrs on the hub.
If the chainsaw is not checked and serviced in time the vibrations and impacts on the crankshaft bearings will increase. This results in costly repairs, serious tool damage.
Important! Manufacturers recommend inspecting the coupling drum when the chain comes into contact with a metal object during sawing.