Standing out in the yard with a revving weed eater isn’t going to do you much good if you can’t get the head to spin. You can pull the throttle over and over, but it still won’t solve the problem. So, before you accidentally cause any more damage to your weed eater, let’s take a look at the possible reasons why your weed wacker won’t spin and how to fix it.
Why Your Weed Eater Head is Not Spinning (The Short Answer)
There are several possible causes why a weed eater runs but the head won’t spin. For example, a broken flex cable, a jammed-up head, a broken head, and a worn-out or damaged centrifugal clutch are all potential causes. You’ll find that with all of these problems, the weed eater’s engine will still run, but the weed wacker won’t spin.
Weed Wacker That Won’t Spin (4 Possible Causes)
If the engine of your weed eater is still working, it means the problem is being caused by something after the engine’s drive shaft. Here is what I believe are the most common reasons your weed eater is not spinning.
Vegetation Jamming the Weed Eater Head
If I’m whacking tall vegetation, like big weeds, then my weed wacker’s head can get clogged up pretty easily. Weeds like vines in the undergrowth are a nightmare for the weed wacker head and can really jam it up. The vegetation gets tangled between the spinning head and the gear head at the end of the shaft.
When you pull the throttle, you’ll find that your weed eater sounds like it bogs down and can only manage a low rev. The clutch is still engaging and trying to spin the head. So, turn your weed eater off and look closely at the head for any jams.
A Snapped Flex Cable Drive
The flex cable is the long flexible cable that joins the clutch to the gear head inside the shaft. Even though they are very durable, they do snap from time to time. This is common if you put the weed wacker under extra stress by cutting heavy vegetation or if you choose to remove the guard and run the weed wacker with longer lines.
When the flexible cable snaps, the weed eater will run on full revs and partly spin the head but stops once the head comes into contact with grass and creates a very loud clanking sound. To check the flex cable, you’ll need to remove the head and gear head and remove the cable.
Damaged Weed Eater Gearhead
Gearheads don’t usually go bad, but if you have an old weed eater, then the gearhead can be the root of your problems. If the gearhead is damaged, you’ll notice that the weed eater will only partly rev as the clutch is engaging and trying to spin the head.
So, you’ll need to remove the gear head and disconnect the flex cable. When you have the gearhead completely removed from the weed eater, try giving it a spin. If you find it hard to turn, then it means the internal bearing has gone bad, probably due to a lack of servicing or grease.
A Worn-Out Clutch
The one part of the drive mechanism you would expect to go bad after some time is the clutch. Every time you engage the spinning head, the centrifugal clutch expands and engages the clutch bell. The parts that engage the bell are the two clutch shoes coated with a high-friction material that is expected to wear down over time.
Once this material completely wears away, the clutch will no longer grip, and the head will stop turning. In addition, depending on your weed eater, one or two springs holding the shoes in place can either come loose or break.
Usually, as the clutch begins to go bad, the weed eater will show signs that something is going on. For example, you could experience the clutch gripping at high revs and jerking the whole weed eater, or you could hear a dinging sound as the sticking shoes pop open and ding the clutch bell.
So, to inspect the clutch mechanism, you’ll need to remove the shaft from the engine and see what’s going on. If you look closely at the clutch, you should see markings indicating how far the clutch shoes can wear down before they need to be replaced. Also, if the shoes are very worn, then there will be damage inside the bell. Finally, if one or two of the springs are damaged, the shoes will probably be displaced or just fall out.
How to Fix a Weed Eater Head that Won’t Spin
I’m hoping that by going over the common causes above, you have discovered why your weed eater head won’t spin. If you have, then here are the fixes you can follow to get your weed eater up and running again.
Clearing the Weed Wacker Head
To clear the head, I find that if you spin the head in the opposite direction, the junk will come out by itself. For any tough vines, a pair of garden snips comes in handy.
If getting everything out of the head is difficult, then you might need to remove the head completely. If you remove the line and the spool, you’ll find some type of screw. So, grab a screwdriver, or Torx screwdrivers for those Stihl weed whackers, and remove the head. Once you have the head removed, clearing the obstruction should be straightforward.
Tools & Parts to Clear A Clogged Head
- Garden Snips
- Screwdriver
Replacing the Gearhead
If your trimmer head is not spinning because of the gearhead, then you’ll need to remove the head from the shaft. To do this, use a screwdriver and release the mounting screw from the head.
Once it’s loose, you should be able to pull the gear head from the shaft. If you feel that it’s pulling on something, then it’s probably the flex cable. You’ll need to give it a bit of a tug to release it. When it finally comes free, remove it from the string trimmer and set it to one side.
Next, grab your new gearhead and align it to the flex cable. Once the gear is lined up, push it onto the shaft and tighten the mounting screw. The last job is to remove the head, line, and spool from the old gearhead and attach it to the new gearhead.
Tools & Parts to Replace a Gear Head
- Screwdriver
- Replacement Gear Head
Replacing the Flex Cable
To replace the flex cable, you first need to remove the shaft from the engine. Once the shaft is disconnected from the engine, you’ll see that the clutch bell will be exposed. Then, pull the bell and the broken flex cable from the shaft.
Now, if you look inside the bell, you’ll see a screw that attached the bell to the flex cable. So, use your screwdriver to remove the screw and then the bell. Next, head to the other end of the shaft and remove the gear head using your screwdriver. Once you have the gear head loose, pull it from the shaft along with the flex cable.
Finally, remove the broken flex cable from the head. Now that the broken cable has been removed, it is time to install the replacement part. So, grab your new cable and check both ends to know which is the top and which is the bottom.
There isn’t a particular end to start with, but I find starting with the gearhead end easier. So, thread the cable into the shaft starting from the bottom and leave several inches hanging out of the bottom of the shaft. Then attach the cable to the gear head.
Usually, you’ll find that the cable has a square end that fits into the gear in a particular way. This can be pretty fiddly, but as long as you line it up correctly, it should go in. Once you have it attached, you can reinstall the gear head.
Next, head to the opposite end of the shaft and attach the clutch bell to the shaft. This should be a case of just reattaching the bell. Once this is done, give the head a spin and make sure everything spins nice and smoothly. Finally, reattach the shaft to the engine, making sure that the clutch fits into the clutch bell.
Tools & Parts to Replace the Flex Cable
- Screwdriver
- Replacement Flex Cable
Replacing the Centrifugal Clutch
The last fix on the list for a weed eater head not spinning is replacing the centrifugal clutch. As I mentioned before, this is the one replacement you should expect to do at some point during your weed eater’s lifespan. So, let’s take a look at the steps you’ll need to follow.
First, remove the shaft from the engine so that you have access to the clutch. Then, take a screwdriver and remove the bolts that hold the clutch shoes to the engine. If you find that the screws are difficult to remove, try spraying them with WD-40 and allow it to soak in for a minute.
Also, you may want to get an extra set of hands because as you turn your screwdriver, the engine will spin at the same time. So, some help stopping the clutch and engine from spinning would be a big help.
Once you manage to get the screws out, you can lift the old clutch off the engine and set it to one side. Next, grab your new clutch shoes and spring and place them onto the mounting pins, making sure you have the clutch orientation correct. If you take a look at the shoes, you should find an arrow showing you the direction they should spin. So, place the shoes on the pin with the arrows pointing in the correct direction.
Next, take the screws you removed from the old clutch and install them on the new clutch. Finally, reattach the shaft.
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