Scratching my head over my Stihl Weed Wacker

[Sigarms]

Up in PA last week visiting my dad with my boys. Took my Stihl weed wacker up along with the blade because I know there are areas my dad (now 86) won't touch just because it wears him out.

Put a good 4 hours on the weedwacker, about 2 of them with the 3 prong black steel blade. Have had that blade for a good 5 years and it has held up VERY well.

Well, I just wanted to finish some things up before leaving, and when I was towards the end of finishing up, the weedwacker felt "strange" (had the blade on it). Turned the machine off, and this is what I found...



I picked up a new blade and thrust plate back in NC, and talking with the guy at the hardware store, he had no clue what happened.

How in the heck does the blade and a good portion of the thrust plate come off when the locking screw is still in place and tight????

Did it just sheer off into pieces?

Just curious if this has happened to anyone here?

 

[RNeumann]

I'm thinking a small crack grew with time and use. It finally traveled to the edge or middle (depending on where it started) and came off.
A saw blade would see a fraction of the use a weed wacker blade would see. You will have to figure a new way to gauge replacement to prevent future failures.

 

[Sigarms]

I can agree with your line of reasoning, however, that does not explain the disappearance of the "top plate" of the thrust plate the blade was sitting on (missing in the picture as well). If only the blade were missing, it's easier to explain, but with that thrust plate missing, I'm just shaking my head.

 

[QRTRHRS]

Take the nut off and see if there is a "new" washer under it. I just replaced the plate on my FS90 because it tore out. I had this happen at least once with my old FS200 but it took a lot more run time before it happened.

I bought this FS90 off a friend who sold it because it was to heavy for him which is true, he is not in good shape. I don't much care for the four cycle engine. It does not seem to build the rpm's you need to cut brush. I was working it pretty hard to do just that when I tore out the center.

 

[oosik]

I have a Stihl FS350. I had a black steel "three prong" blade that developed a stress fracture, finally failed and just flew off like a bat on the way to Hades. Fortunately it hit nothing on its way.