How Tough is the STIHL FS 91? We Torture-Tested it to Find Out
STIHL string trimmers have a reputation for being absolute tanks. They're known for their reliability and ability to withstand serious abuse, especially in the hands of lawn care professionals. But how tough are they really? We decided to find out by putting the popular STIHL FS 91 to the ultimate durability test.
Stu and Chip from Main Street Mower subjected this poor trimmer to a series of increasingly ridiculous challenges. They didn't hold back, pushing the FS 91 far beyond what any sane person would consider normal use.
So, how did it hold up? Let's break down each stage of this epic gauntlet of destruction.
The Gauntlet of Destruction: Nine Brutal Tests
We're breaking down each of the tests from the video so you know what this STIHL FS 91 had to endure.
Test 1: The Bump Head Massacre
The first test focused on the bump head. The goal? To see how many times it could be bumped on the concrete before it failed.
Stu and Chip went to town, aggressively slamming the bump head against the hard surface. The result? The trimmer ran out of string very quickly. They estimated it only lasted for a few thousand bumps, which is actually quite impressive considering the extreme force they were using.
In a typical yard, the bump head comes into contact with softer surfaces like grass and soil. This test simulated repeated, forceful impacts against solid concrete, which is far more demanding than normal use.
Test 2: Flexing the Handle and Overheating
Next up was a two-part challenge: stressing the handle and pushing the engine to its limit.
The guys were bending and flexing the handle with extreme force. At the same time, they ran the engine at full throttle for an extended period. This led to some melting around the edges of the engine housing. It also made the engine scorching hot.
Despite this abuse, the trimmer kept running. It didn't stall or seize up, which speaks to the engine's resilience.
Test 3: Asphalt and Concrete Dragging
Time to get rough! Stu and Chip dragged the FS 91 along both asphalt and concrete. They wanted to see how well it would hold up to abrasion and impacts.
At one point, they joked that the asphalt was "too puny," implying it wasn't doing enough damage.
Test 4: The Drop Test
How many times can you drop a string trimmer and still have it start up? That was the question for this test.
Stu and Chip repeatedly dropped the FS 91 onto the hard ground. After several drops, the shaft developed a "slight curve" or "waffle" as they called it.
Here's the impressive part: after each drop, the trimmer started on the very first pull. Even with a bent shaft, the engine continued to perform reliably.
Test 5: Continued Dragging and Aluminum Limitations
Back to dragging! This time, the focus was on the limitations of the materials used in the trimmer's construction, specifically aluminum and steel.
After more dragging, the FS 91 showed cosmetic damage, but it was still in surprisingly good condition.
Test 6: The "Official STIHL Technique" - Shaft Straightening
This part was more for laughs than scientific rigor. The shaft had taken a beating, so Stu and Chip attempted to straighten it using what they called the "official STIHL technique."
They simply bent it back into shape by hand.
"This spot needs a little straightening," one of them said.
It wasn't a perfect fix, but it was enough to improve the trimmer's overall alignment.
Test 7: Submersion in the Retention Pond
Things took a turn for the aquatic when the duo tossed the FS 91 into a retention pond. They fully submerged it, leaving only the air filter exposed.
After retrieving the trimmer from its impromptu bath, it started on the first pull. However, the gearbox started grinding on the rocks as they moved it around in the water.
Even with waterlogged components and a damaged gearbox, the engine kept running.
Test 8: Dirt Ingestion – The Ultimate Sin
This test was brutal. Stu and Chip removed the air filter and deliberately shoved dirt directly into the air intake and grease housing.
They wanted to simulate the effects of years of neglect and abuse. This is something no lawn equipment should endure.
Even with dirt in its system, the FS 91 stubbornly sputtered back to life.
Test 9: The Toss
For the grand finale, Stu and Chip decided to hurl the string trimmer across the parking lot.
After the toss, it still worked!
Autopsy: The Final Verdict
After all that punishment, something finally gave way.
The carburetor broke off, bringing the torture test to an end.
Stu admitted, with a hint of irony, that the FS 91 was "not very durable." He followed that up with a joke about bringing it back with a 7-day return policy.
Final Thoughts: Durability vs. Abuse
So, is the STIHL FS 91 durable?
On one hand, it survived an absolutely insane amount of abuse. It was bumped, dragged, dropped, submerged, and filled with dirt. It kept running through almost all of it.
On the other hand, it did eventually break. The carburetor couldn't handle being used as a pogo stick.
It's important to remember that these tests were far beyond the scope of normal use. This wasn't a test of durability; it was a test of destruction.
Still, this extreme experiment reveals a lot about the FS 91's potential weak points. It also demonstrates just how much punishment a STIHL trimmer can withstand before finally giving up the ghost.
Which product should Main Street Mower destroy next? Let them know in the comments section of the video!
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Disclaimer
The tests shown in this video were performed under controlled conditions. Do not attempt to replicate these tests. Abusing your power equipment can be dangerous and will void your warranty.
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