View Full Version : stihl fs 85 troubles

The Intimidator
01-12-2007, 04:19 PM
hey fellas I just recently acquired a used fs85 it was making a loud clanging noise so the lady went and bought her hubby a new one lol My first thought was ok it is just the clutch I get the engine out of the enclosure hmm the clutch is all in one piece it is all clearly worn although nothing is broken. I was looking around and it seems as if the flywheel is moving independently of the crank and the crank is moving independently of the piston :rolleyes: thinking this isn't good I got the clutch off and I can't get the flywheel off of the crank? More inspecting I take the exhaust and carb off and there is a fair amount of carbon built up looking at the piston it seems ok although there is some carbon built up on it too. I figured while I am in here I might as well pull the head and inspect the piston and clean the carbon out of the head. So here I am now with the engine pulled apart on my bench wondering what all I should inspect while I am in here? I know I need new rings and a gasket set I broke one of the rings on removal it was not stuck I just caught it on the head lol what do you guy's recommend me to do while I have this thing on the bench? I also need to know how to get the flywheel off and the torque on the head bolts? I also discovered that the clutch most likely is the cause of the problem :laugh: on closer inspection the middle piece of the shoe that rides on the clutch itself is broken Right off on one and the others are all cracked anyone have a decent used clutch? thanks

01-12-2007, 04:55 PM
I am not sure I followed all your descriptions very well. I have an FS-85 trimmer, and have had the clutch apart. In my case, one of the springs holding the shoes apart when idling broke. I replaced the spring, and I was good to go again.

You don't say much about the clanging noise, where you think it is coming from, frequency, consistency, longevity, etc.

However, I am not sure why you want to take the flywheel off the crank. If I remember correctly, the flywheel contains the "dogs" (I don't know the right term, but the shoe-like pieces that engage when running WOT). I seem to remember the tube-end of the connection, that is the part where the throttle handle, and the shaft running the gearbox at the end are contained, has a concave dish. The dish is connected to the sold steel shaft running down the tube to the gearbox.

The flywheel with the dogs fit snuggly into the dish (about 1/2-3/4" deep, 4-5" diameter). The flywheel runs independently of the dish when starting. But, when the engine is reved up in rpms, the springs on adjacent dogs will extend due to centrifigal force, engaging the dogs on the inside rim of the dish. When running at WOT, the centrifigal force of the dogs will engage fully with the dish, so that there is no slippage between the flywheel and the dish.

I'm not sure I have explained this very well. But, I repeat my earlier question about why you feel you need to remove the flywheel. Everything associated with the clutch is fully exposed when you pull the two sections apart (the power head, the tube/handle assembly).

The exhaust ports can be cleaned out after taking off the muffler. Keeping these ports clean, just as any 2 cycle engine, is important. I have never taken the head off my engine -- only asking for more trouble with removal/reassembly. My trimmer has seen 4-5 seasons of hard use.

BTW, after 2 seasons, I switched from Stihl oil for fuel mixture, to Amsoil and Opti-2 synthetic oils. Buildup of carbon in the exhaust ports has never been a problem since the switch. When reconditioning my trimmer this offseason, I didn't even take the muffler off to check for exhaust port buildup. I have not found anything there the last couple of times on this piece, as well as other Stihl pieces that are also running on Opti-2 oil.

The Intimidator
01-12-2007, 05:17 PM
hmm I guess pics would help I would like to pull the flywheel to check the key I have a odd feeling that is is sheared off the flywheel.

The only reason I pulled the head was to get a better idea of what is going on inside the engine and to make sure everything is in working order and clean it out. It is obvious the trimmer has been run hard and I would guess it has been used for 5 or six years maybe more I am hoping to replace any broken parts and clean it up to use for this season as I don't have a commercial trimmer right now and the fs80 and 85 are still selling around 500$ up here so if I can get this one operating correctly I will be set.

I know I should have probably left the engine as a whole alone but one thing led to another and I like tinkering with stuff anyways and they are fairly simple to work on thanks for the help The dogs you are referring to are the clutch shoes and the dish would be the drum I have a good idea how they operate I just did't look close enough to see the cracks in the clutch lol I'll go shoot some pics for you guy's to have a look

The Intimidator
01-12-2007, 05:40 PM
The wonderful pile of parts

The bottom end with the piston hanging out

the top end ready for cleaning and possible honing



the shiny areas is were the shoe or dog move on the centre piece you can see the one shoe is broken and the others are cracked I am looking for a used assy unless the big dealer can get me one cause the small stihl guy in town says he cant get them I am pretty certain that is where the noise is coming from thanks

01-12-2007, 09:45 PM
Well, you have it broken down more than I ever had mine broken down! I don't have enough confidence in my mechanics skills to get this far, with the intention of getting it back together.

Your assessment of the broken shoe being the source of the clanking is a good one. They are cast iron (if I remember corrrectly), so would make a real noise banging off the thin, metal drum.

Your pic does not show any springs, so you must have taken them off already. I would be concerned as to WHY one of the dogs are broken. Maybe a spring broke, allowing two of them to get loose inside the cavity, and the banging around caused it to break. I don't see how it would break during the normal operations of the trimmer.

You should have no problem getting any parts you need. I am baffled why your "small stihl guy" can't get the parts. Perhaps try a larger dealer. These are the same parts used for the FC85 edger, and maybe other Stihl power units as well.

Keep us posted on your progress.

Oh yes, a new trimming is far less than the $500 you assumed.

The Intimidator
01-12-2007, 10:01 PM
actually us canucks seem to get screwed on everything compared to you guy's The cheapest quote I have got on a fs85 is 420+tax from a unknown dealer my regular dealer quoted me 450$ and when I was inquiring about the parts today I was told 484$+tax on the fs 85 granted I could probably walk out with one from the dealer in the country for 440$ otd but the local guy said he could go no lower :dizzy:

I can get the springs and the shoes no problem he can't get the complete assembly or just the center piece that threads onto the flywheel and holds the clutch together. I am really contemplating buying a new trimmer as it stands right now I am looking at around 175$ for the new clutch assembly+ drum, rings and gaskets and if the flywheel is fudged up I will be looking at around 200$ in parts for a old machine I am considering the honda or another fs-85 I only hear good things about the stihl but I can get the 25cc honda for 400$ otd hmm I should probably start a new post thanks for the help I'll do a right up and take some more pics for you guy's as a sort of guide to disassembling a fs-85 power head

EDIT.............I was once told by a friend of mine that it is all just nuts and bolts with a few precision parts and torque on the fasteners spread about and if a man made it then we can sure as he!! take er apart and put it back together mind you we are what most would consider rednecks and backyard mechanics but we seem to get along ok with our projects :laugh:

double edit lol.... that is the back side of the clutch in the pics all the springs are attached and none of them are brocken thanks again for the help

01-12-2007, 10:16 PM
I have some stihl trimmers so I don't want to bash them or your decision to buy them. I want to point out that the main reason I stay with Echo is because they are easier to work on and parts aren't that expensive. The clutch shoes and ring would be around $60 and can be replaced without a tear down of the machine, only taking the front part off. Even a broken trottle cable turned out to be a big deal on my Stihl because they had three different part.

01-13-2007, 08:18 AM
I'm sorry, I missed the point of Canadian dollars. The dealerships in the US are not stocking the FS-85 any longer - at least I have not seen any in the past year, or more. The newer, comparable models (4-mix) are in the low $300s.

01-13-2007, 09:25 AM
I know Envy had an issue with his stihl trimmer, IT was the flywheel key that was broken and the way it is made you have to replace the entire drum and it was $$$$$$


01-13-2007, 09:36 AM
Here is the thread, may or may not be of any help along the way