It’s pretty common for a trimmer head to spin at idle, and it is more than likely an issue every gas-powered trimmer owner will face at some point. Thankfully this repair is easy to both diagnose and repair, and you’ll be up and running in no time at all. So, how do you find out what’s causing your trimmer head to spin at idle? Let’s take a look.
Why Does My Trimmer Head Spin At Idle? (The Short Answer)
Connecting the trimmer’s engine to the driveshaft is a centrifugal clutch that engages when the motor reaches a certain RPM. If the trimmer head spins at idle, the clutch is stuck open, resulting in the clutch being unable to retract. Usually, this issue is caused by corrosion within the clutch or an issue with the clutch spring.
Possible Causes of A Trimmer Head That Won’t Stop Spinning (2 Things to Check)
So there are two main reasons why your trimmer’s clutch is sticking open and causing the trimmer’s head to spin at idle. Let’s take a closer look at these two issues and see how to diagnose the specific cause. But first, let me show you where to find the clutch on your weed eater.
Gaining Access to the Clutch
Before you can diagnose the issue with the clutch, you’ll first need to get to the clutch location. To do this, you’ll need to remove the main shaft from the weed eater. Here’s an example of how to access the clutch on a Stihl FS-110. This process is going to be pretty much the same for most gas-powered trimmers.
- Remove the Spark Plug Connector
- Remove the Engine Cover Mounting Bolts
- Remove the Engine Cover
- Remove the Main Shaft Mounting Bolt
- Pull the Main Shaft from the Engine
The only tool you’ll need to complete this process is a screwdriver. In this example, you’ll need a Stihl Torx screwdriver.
Checking the Clutch Spring
Once you remove the main shaft from your weed eater, you can access both sections of the clutch. In one section, you’ll find the clutch bell attached to the main shaft. The other section is where the clutch shoes and spring are attached to the engine.
The first thing you’ll want to check is whether or not the spring is in place, connecting both shoes together. If the spring isn’t properly in place, then you’ll have diagnosed why your trimmer head spins at idle. If the spring doesn’t hold the clutch shoes together, then the shoes stay open and make contact with the clutch bell attached to the main shaft. Springs usually fail for two reasons. The spring either breaks or comes off of the shoes.
So, if the spring is broken, it will need to be replaced. If the spring is intact, then it will need to be reattached to connect both of the clutch shoes back together.
Checking for Clutch Corrosion
If you closely inspect where the two clutch shoes are attached to the engine, you’ll find two mounting bolts—one for each shoe. These bolts keep the clutch shoes positioned on the two shafts and allow the clutch to open and close.
Basically, the shoes open as the engine revs, then the spring pulls the shoes back into place when the engine idles. Any corrosion on the mounting points of either shaft can prevent this action from happening.
So, keeping these mounting points free of corrosion is vital. An easy way to check the mounting points is to try to open and close both of the shoes manually. If you find the shoes hard to open and close and the spring is correctly installed, then corrosion is likely the issue.
How to Fix a Trimmer Head That Spins At Idle
Now that you have diagnosed why your trimmer head spins at idle, it’s time to go over the three different repairs. Here are all the steps for the three fixes and all the tools and parts you’ll need. Let’s take a closer look.
Replacing a Trimmer Clutch Spring
The first step to replace the clutch spring on your trimmer is to remove the old clutch shoes. So, using the Stihl trimmer as an example, grab your Torx screwdriver and remove both bolts securing the shoes to the engine. Then, lift off the small metal cover plate that protects the shoes. Next, lift the old shoes off of the mounting points.
Now, lay both your clutch shoes on a flat surface and position them so that they face each other the same way they were mounted on the trimmer. Then, hook one end of your replacement spring onto one shoe and the other end on the other shoe. This can be tricky to do since the spring is so small. A pair of pliers, grips, or a small spring puller that is small enough to grip the spring and connect it correctly can help.
Next, mount your reassembled clutch shoes and spring them back onto your trimmer. Then, reinstall the metal cover plate and install the two mounting bolts. Finally, put the trimmer back together again and give your trimmer a try.
The only thing I would say about replacing a clutch spring is that it can be very fiddly and, for some people, might be too much of a struggle. So, you can always just replace the clutch shoes and spring with a replacement kit that is already assembled. A spring by itself will cost around $1, and a kit will cost around $20. So, it’s not too much of an expense if you choose to go with the kit. Also, you’ll get the benefits of new clutch shoes.
Tools & Parts to Replace a Clutch Spring
- Pair of pliers
- Spring Puller
- Replacement Clutch Spring
Tools & Parts to Install a Clutch Shoes Kit
- Replacement Clutch Shoe & Spring Kit
Repositioning a Trimmer Clutch Spring
This fix is exactly the same as installing a new spring. The only difference is that you’ll be using the old spring instead of a new one. So it’s the exact same method and the same set of tools. But, again, if you don’t want the hassle of messing around with the spring, you can just install a clutch shoe kit with the spring already installed.
Removing Corrosion from a Trimmer Clutch Shoe
To clean off the corrosion from your trimmer clutch, you’ll first need to remove the clutch shoes and spring. So, use your screwdriver or, in this case, your Torx screwdriver and remove the two mounting bolts. Then lift off the metal cover plate and the clutch. Just be careful when removing the clutch, and make sure the spring doesn’t come off, or you’ll have the awkward task of reinstalling the spring.
With the clutch shoes removed, run a small piece of sandpaper on both mounting shafts and remove any corrosion. Then, take a small round metal file or a piece of rolled-up sandpaper and clean out the clutch shoe holes that fit over the mounting shafts.
Next, use a small amount of lubricant on the clutch shoe mounting holes and the mounting shafts. I usually use a couple of drops of 3-1 oil to add lubrication and some preventative corrosion protection. Finally, reassemble your clutch and put the rest of the trimmer back together. Hopefully, this will fix your weed eater head that won’t stop spinning.
Tools To Remove Corrosion from a Trimmer Clutch
- Small Round Metal File
- 3-1 Oil