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Broken clutch - STIHL FS 86 brush cutter

Stihl FS 86Today was the time to maintain the surroundings of my land. For that I preferred to use my FS 86 STIHL brushcutter ( year of production 1989 ) rather than the CB 38 edger.
One detail surprised me immediately after starting the engine is that the head was idling jerkily, with jerks that went up to the handlebars ... weird ... the machine however correctly performed its job, it took its turns well and the vibrations and other jerks disappeared with acceleration.

I am the only user of this machine for which I perform regular maintenance, and only with a wire head ( square section 2.4 mm ). It is true that I have already found myself stuck in particular in the fence, but from there to break the clutch!

At the end of the work I decided to take a closer look. Engine stopped, I began to manually turn my head in both directions to see what it was. In the normal direction of rotation, no real worries, the rotation seems free to me, but in the opposite direction, important points of blockage appear from time to time!

view of broken clutch ...Mandatory autopsy, dismantling of the machine. In the first place I believed in a possible problem with the idler gear at the end of the shaft because the jerks were much more noticeable near the head, but the reduction gear is intact and perfectly greased. Disassembly and extraction of the clutch ( well ... of what remains of it ... ) with a socket of 13 then recovery of the remaining pieces, trapped in the crankcase.
 
what's left of the clutch ...A breaking point clearly appears at the level of the tension spring hook. This clutch is not the original one, I already replaced it in 2013 because it is a bit "tired". This time it will not have had much time to wear out! However, I had bought this part from a French supplier STIHL and not in China. Perhaps a "straw" in the cast iron ... I was left with a dismantling and cleaning of the engine block as well as the casings, this in order to eliminate as much as possible the small debris of cast iron which did not have failed to diffuse in the interstices, then to check the good condition of the clutch housing ( 4126 160 2900 ) which I will not be able to replace, part exhausted.
 
I took the opportunity to complete the filling of grease in the angle transmission, I only need the new parts which will arrive these days, and it will be able to resume its service.
 
Here are some pictures of the two pieces making up one of the weights:
clutch002 (160x120px]clutch003 [160x120px]clutch004 [160x120px]clutch005 [160x120px]
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