A sprocket is one of the crucial mechanical components in a chainsaw. It essentially transfers torque to the cutting chain. Hence, sprocket maintenance becomes critical as you are looking to extract maximum available power from the engine for your cutting chain. This blog post shall provide an average chainsaw user with all the guidance he needs to repair and maintain a sprocket on his own.
Chainsaw sprocket. Tips from a professional.
A chainsaw sprocket (rim or spur type) is mounted coaxially with the clutch drum and has the cutting chain passing over it. Sprockets wear out due to their extended use, resulting in chain misalignment, loosening, and vibrations during use. They should be replaced roughly after every two new chains. To replace a sprocket, hold the piston’s movement and remove the clutch disc and the washers holding it in place before installing a new sprocket.
In this blog post, I will explain in more detail what a chainsaw sprocket does and when and how to replace it.
- 1 What is a Sprocket on a Chainsaw?
- 2 How do you Identify a Chainsaw Sprocket?
- 3 Which is Better Rim Sprocket or Spur Sprocket?
- 4 When should a Chainsaw Sprocket be Replaced?
- 5 What does a Worn Chainsaw Sprocket Look like?
- 6 Are all Chainsaw Sprockets Interchangeable?
- 7 How do you Replace a Clutch Sprocket on a Chainsaw?
- 8 How do you Replace a Chainsaw Sprocket?
What is a Sprocket on a Chainsaw?
A sprocket transfers power from the crankshaft to the chain, enabling it to slide along the guide bar. The sprocket is coupled with the clutch drum and crankshaft and rotates coaxially on the same axis.
The cutting mechanism of the chainsaw consists of the guide bar, chain, clutch drum, and sprocket. The sprocket serves a crucial function as it presses the cutting chain firmly against its teeth and transmits the engine’s rotational kinetic energy to the chain.
These sprockets are mounted to the clutch drum, which is connected to the engine’s crankshaft. Two main sprocket types are used in chainsaws: the rim sprocket and spur sprocket.
How do you Identify a Chainsaw Sprocket?
Sprockets are either of a rim or spur type. They are often gauged in terms of their pitch and number of teeth/slots.
To access your chainsaw’s sprocket, remove the clutch cover located on the right side of the chainsaw. Your sprocket can either be a rim or spur sprocket. Spur sprockets are star-shaped and have multiple teeth located at their circumference. Whereas in rim sprockets, these teeth are sandwiched between two discs.
While dealing with sprockets, you need to remember their pitch and the number of teeth/slots. Pitch is the circumferential distance between consecutive sprocket teeth. In the case of a chain, it is the distance between three consecutive drive rivets. Note that the pitch of your sprocket must match that of the chain so it can mesh easily.
Pitch is typically measured in inches. The smallest pitch you’ll find will be 1/4”, while the largest would be 3/4”. Most sprockets have a pitch of 3/8 inches. Apart from the pitch, another important ID parameter is your sprocket’s number of teeth/slots. For spur sprockets, the number of teeth is counted, while for the rim type, the number of slots is considered.
The manufacturer usually marks the pitch value along with the teeth number on the sprocket. Once the sprocket ID is known, you can purchase a new one from an online store or your local dealer.
Which is Better Rim Sprocket or Spur Sprocket?
I think using a rim sprocket should be preferred as it provides a smooth chain rotation, requires lesser maintenance, and is cheaper.
Using either of the two sprocket types has no major effect on the chainsaw’s performance. However, there are certain advantages due to which you might consider switching your sprocket from a spur type to a rim sprocket.
● Advantage 1: Replaceability:
Rim sprockets are easier to replace than spur ones as they are mounted on the clutch drum with a splined hub. To remove them, only a washer and an E-clip must be taken out, and the replacement can be performed easily.
● Advantage 2: Chain Alignment:
Rim sprockets self-align the chain on the guide bar rails. Due to a better lateral alignment, the chain provides a smooth cutting operation and prevents the guide bar from wear due to derailment.
● Advantage 3: Wear Rate:
Probably the biggest disadvantage of spur sprockets is that they subject the chain to a high wear rate. They also cause the drive links to bur when the chain jumps off the bar groove. Chains with rim sprockets have a longer life than those with spur sprockets.
● Advantage 4: Cost:
Not only are rim sprockets easily replaceable, but they are also cheaper than their spur counterparts. Spur sprockets cost around 22-30$, while a single-rim sprocket could fall around 7-8$.
Apart from these advantages, there are certain areas where a spur sprocket would stand out. For example, a spur sprocket is more durable than a rim sprocket due to its simpler build. It is made up of a single part and not an assembly, as in the case of rim sprockets. Furthermore, it is easier to install the chain on a spur sprocket than on a rim sprocket.
Considering these pros and cons, you can make a choice that suits your needs. However, I prefer rim sprockets as they are much easier on the cutting chain and cause it to run smoothly. A chain that is in good working condition would indeed ensure top-notch performance.
When should a Chainsaw Sprocket be Replaced?
In general, a chainsaw sprocket should be replaced after every two chain replacements. Inspect the sprocket if the chain gets derailed or gets loose frequently or if the chainsaw vibrates while cutting. Replace it if necessary.
Chainsaw sprockets are made up of hardened steel. Hence, they need not be replaced frequently. However, this also prevents them from getting noticed that much. Since they drive the chain and at the receiving end of all the wear that comes with it, sprockets do tend to get damaged. When they get worn out, replacing a sprocket is better than repairing it.
Let’s look at the signs when you should consider replacing your chainsaw sprocket.
● Sign 1: Chain Wear & Tear:
When the sprocket wears out, the chain gets derailed quite easily, and you might need to tension your chain quite frequently in this case. Using a worn-out sprocket can affect your chains adversely, and, in some cases, you may require a new chain.
● Sign 2: Performance Hitches:
A damaged sprocket may result in continuous vibrations during use. Sometimes, the chain may seem to slip off the guide bar when the throttle is pressed. You might witness a loss of torque when the engine is loaded, and the chain may tend to loosen or get derailed more frequently than normal. Under all these circumstances, you should inspect your chainsaw’s sprocket and check for any apparent signs of damage.
● Sign 3: Visual Signs:
Upon inspection, your sprocket’s teeth might have some metal chipped off instead of being smooth and consistent. This typically occurs in the case of spur sprockets. In this condition, the sprocket should no longer be operated. Examine the channels where the drive links fit for rim sprockets and check for chipped-off metal pieces. Replace the sprocket if the damage has been confirmed.
Apart from this replacement during operation, scheduled replacements of sprockets can be and should be carried out. Generally, one sprocket replacement should come after every two chain replacements.
What does a Worn Chainsaw Sprocket Look like?
A worn chainsaw sprocket may have signs of grooves or notches or uneven teeth. As a result, the chain will not rotate smoothly on the guide bar.
Chainsaw sprockets are exposed to various dynamic loads that contribute to a certain amount of fatigue. Since they drive the chains, sprockets must be kept in proper working order. Using a worn sprocket for an extended period would only add to the wear and tear. It may damage other chainsaw components, such as the guide bar, the chain’s drive links, and cutter teeth.
A bad sprocket would also load the engine and rob you of considerable power. To check if your sprocket has worn out, look for signs of wear, such as notches. The sprocket teeth are highly likely to have developed burrs or grooves between them due to the metal being chipped off by the cutters. This causes misalignment in the chain.
Most sprockets have a horizontal line on each side of the driver holes. When the driver holes begin to touch the lines, the sprocket is meant to be replaced. I believe chainsaw sprockets are quite cheap; hence, they should be replaced when needed to keep your chain running smoothly.
Are all Chainsaw Sprockets Interchangeable?
Chainsaw sprockets of different brands are interchangeable as long as they are of the same size. The universal sizes for sprockets are mini, small, and large.
The sizes for these sprockets are 5/8” for mini, 3/4” for small, and 7/8” for large ones. While making a replacement, ensure that the chain pitch matches the sprocket. Usually, the pitch is engraved on the sprocket itself.
Please note that sprockets of the same size can be used universally, even if they are of a different brand. The only thing which needs to be checked is the size of the sprocket. Hence, while making a replacement, check for the sprocket size and ensure that you buy that size from the market.
How do you Replace a Clutch Sprocket on a Chainsaw?
To replace a clutch sprocket, remove the clutch cover and use a special tool to disengage the clutch disc from the sprocket drum. Take off the clutch and the sprocket and install a new one.
Using the same procedure, you can replace the clutch and the sprocket on your chainsaw. The step-by-step method is provided below:
● Step 1: Remove the clutch cover and chain:
The first step is to unscrew the nuts securing the clutch cover on the right side to make both visible. Now, remove the chain from the guide bar and remove the guide bar subsequently.
● Step 2: Block the piston:
The clutch is mounted on the same shaft as the sprocket. To take the clutch off, you must first ensure that the piston doesn’t rotate. You can remove the spark plug and insert a rope into the cylinder to prevent the piston from moving.
Pulling the chord out first and then inserting the rope into the cylinder block is better. Then release the pull chord after the piston doesn’t rotate. This step ensures that your pull chord assembly isn’t loaded when you remove the piston; hence, the load would be switched to the piston instead.
● Step 3: Take off the clutch:
Use a clutch removal tool to lock onto the clutch. If it is reverse threaded, rotate the tool clockwise until it loosens. If a clutch removal tool is unavailable, use a screwdriver and a hammer combined to loosen up the clutch. Once the clutch is loose, remove it entirely from the assembly.
● Step 4: Reinstall:
Remove the chainsaw sprocket if needed. After attaching the new sprocket and the clutch drum, tighten the clutch in the opposite direction. Then using a clutch removal wrench, tighten it all the way. Reattach the guide bar and the chain. Your clutch replacement procedure is now complete.
How do you Replace a Chainsaw Sprocket?
Replacing a sprocket follows the same procedure shown above. In some chainsaws, you need to remove E-clips additionally to remove the sprocket from the clutch drum.
Most spur sprockets are welded on the clutch drum and come as a single part. Hence, you need to remove the clutch disc and replace the sprocket disc. The removal of the clutch disc is discussed in detail in the previous section. While performing this removal, ensure you lock the piston and rotate the clutch disc in the right direction.
Once the clutch disc is removed, the sprocket and the drum are free to be removed, and a new sprocket can be installed.
Please remember that in some chainsaws, the sprocket is present at the front, and the clutch drum at the back. In that case, you would need to remove the sprocket first and then the clutch drum (if needed). To remove the sprocket in that case, a washer and an E-clip must be taken out. You can use a screwdriver to do that.
After installing the new sprocket, place the washer and insert the E-clip back again. This procedure would also be valid for rim sprockets and spur sprockets having the clutch located at the back.