Stihl FS45 - head problems

[danijelm]

Hi to everyone,

I got a used trimmer FS45 curved shaft. The carburetor had a faulty check valve, so I changed it and now the engine runs great, but I noticed a new problem.

After a few minutes of mowing, the head starts to turn with difficulty. I think it happens when I slam it into the ground and that plastic nut tightens. After that, the head and the last 10 cm of the shaft become extremely hot. if I loosen the nut a little, the head turns freely again. I took off my head and examined the bearing. The bearing seems fine to me, there is grease, it turns freely and if I drive at full throttle for a few minutes without the head, there is nothing hot. The hex plastic slot for the nut on the head is slightly damaged, I think someone misplaced it in the past. There is no grass around the head for it to stick to. I cleaned the part of the guard that goes around the head and it sure doesn't get stuck.

My question is whether to change the head or is the problem somewhere else. The shaft is lubricated. I don't have a picture of the head right now, but I think the original is a stihl. Is it possible that the head is standing crooked due to a damaged fit, and because of that it continues to heat up and deform further?!?

I have an FS36 with an older type of head (completely black), can the heads be replaced to see if that is the problem. I ask this because my FS45 and FS36 are not in the same place and I need to remove the head and bring it to another location. Sorry for the long text, I hope someone has an idea how to solve the problem. Thank you in advance.

Danijel

 

[StarTech]

According the Stihl head info I have no they will not interchange.

 

[StarTech]

Also it is possible the bushing is worn badly. If so might be a good time to up to a longer 45L curve shaft if you are a tall person.

 

[danijelm]

I solved the problem.
Bearing was defective. the nut that goes into the plastic part of the head had an axial movement of about 2 mm.
when the head is tightened by hand, everything is fine, but during operation, the plastic cap tightens by rotation, the shaft is pulled down and friction is created at the upper bronze plate. The shaft turns more and more difficult. I haven't been able to figure out why this is happening. maybe some manufacturing defect?
new bearing is €12. Not bad.

Thanks for your help

 

[ElectroGuy]

I solved the problem.
Bearing was defective. the nut that goes into the plastic part of the head had an axial movement of about 2 mm.
when the head is tightened by hand, everything is fine, but during operation, the plastic cap tightens by rotation, the shaft is pulled down and friction is created at the upper bronze plate. The shaft turns more and more difficult. I haven't been able to figure out why this is happening. maybe some manufacturing defect?
new bearing is €12. Not bad.

Thanks for your help

Is that nut supposed to spin at all? I have the same problem and the nut spins freely, I'm thinking it's supposed to be holding tight to the shaft , otherwise it just tightens up the cap nut as you described.

 

[StarTech]

Well yes it is suppose to rotate if it is the one in the following picture of a disassembled flex shaft to trimmer head adapter that is at the end on the curved tube. These adapters are not meant to taken apart not are they available separate from the curve tube. The arrows are pointing to the two bronze bushings that are in the adapter.


The 16mm hex is machined on the shaft.

 

[ElectroGuy]

Well yes it is suppose to rotate if it is the one in the following picture of a disassembled flex shaft to trimmer head adapter that is at the end on the curved tube. These adapters are not meant to taken apart not are they available separate from the curve tube. The arrows are pointing to the two bronze bushings that are in the adapter.

View attachment 65343
The 16mm hex is machined on the shaft.

But the 16mm nut that you mention as machined to the shaft, that shouldn't spin correct? On the one I have that nut is actually spinning on the shaft.