Stihl MS250 chainsaw - clutch
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    Fulliautomatix's Avatar
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    Stihl MS250 chainsaw - clutch

    Anyone have experience with replacing one? I suspect mine is shot, the motor runs fine, but the sprocket/drum doesn't move.
    It appears that there are a number of manufacturers of replacement parts available on Amazon, but I'm a bit skeptical after reading some of the reviews that they may be parts of sketchy origin. Can anyone recommend a reputable online dealer?
    Last edited by Fulliautomatix; 07-17-2017 at 10:56 PM.

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    Drifterbike's Avatar
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    With something has important has a chainsaw I would take it to a Sthil dealer. Its cheaper to buy a new saw than have problems with a repair down the road. Just MY opinion..
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    Tomfive's Avatar
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    Quote Originally Posted by Fulliautomatix View Post
    Anyone have experience with replacing one? I suspect mine is shot, the motor runs fine, but the sprocket/drum doesn't move.
    It appears that there are a number of manufacturers of replacement parts available on Amazon, but I'm a bit skeptical after reading some of the reviews that they may be parts of sketchy origin. Can anyone recommend a reputable online dealer?
    When you say the sprocket/drum does not move, do you mean it is stuck with the engine off, or is it free to move and just not moving when you rev it?

    Is the safety brake on or broken that it will not release, preventing the chain/sprocket/drum from moving? The safety brake will prevent all movement of the chain/sprocket. Doesn't matter if the engine is running or not. It is meant to stop all chain movement, engine/clutch does not have enough umph to overcome the brake. Work the safety brake on and off to see if it is just stuck or the mechanism is broken.

    A bad clutch would allow the chain to move with the engine off, and also would move with the revving the engine. It just won't have any power when placed in wood. I'm not familiar enough with your model, but the clutch can be easily replaced, it is usually just 3 or 4 centrifugal weights with friction material on outer surface, held with small springs to pull it away from the sprocket drum when idling. Replace the weights and a new sprocket/drum and you are usually good to go. Changing springs is a good idea, but not always needed. Not a difficult replacement, but if you're not familiar, easier to get it repaired at a Stihl dealer.

    Brake and clutch are separate mechanisms operating on the same sprocket drum. I haven't seen any clutches go, but I am not a pro chainsaw user. I've seen the brake get stuck on a used saw I purchased because it was put together wrong. That was an easy fix for me.

    Good luck, just my 2 cents.
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    Tom

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    Tomfive's Avatar
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    I had some more thoughts on this last night. If you need to remove the entire clutch from a chainsaw, to service/replace it, or possibly get to the oil pump underneath, you can stuff a piece of rope into the sparkplug hole to hold the piston/crankshaft then unscrew clutch. It's been a long time since I've done this, so I didn't remember it on my earlier reply.

    One additional hint, IIRC is that the clutch has a left hand thread and unscrews backwards from standard screw direction. I think this is true for almost every saw out there.

    More 2 cents.
    Tom

    2011 1026R/R4's -- H120 FEL/49" -- 260 BH/12" -- Bro-Tek Ripper -- Artillian Forks/42" -- 244 lbs JD Rear Wheel Weights -- KBOH Hooks and Clevis' --
    Block heater -- 180* T-stat -- Evans HP Waterless Coolant

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    Fulliautomatix's Avatar
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    Quote Originally Posted by Tomfive View Post
    When you say the sprocket/drum does not move, do you mean it is stuck with the engine off, or is it free to move and just not moving when you rev it?

    Is the safety brake on or broken that it will not release, preventing the chain/sprocket/drum from moving? The safety brake will prevent all movement of the chain/sprocket. Doesn't matter if the engine is running or not. It is meant to stop all chain movement, engine/clutch does not have enough umph to overcome the brake. Work the safety brake on and off to see if it is just stuck or the mechanism is broken.
    Based on your description it sounds like I need to investigate the safety brake instead. (While I did work the safety brake on/off a few times, it had no effect on the situation.) Perhaps the safety brake mechanism is broken. The sprocket/drum/chain is not free to move at all, with the motor off or running. (I took the bar/chain off to test with the motor running). I'll have to pull it apart further tonight.
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    Pull bar, chain and brake off

    Quote Originally Posted by Fulliautomatix View Post
    Based on your description it sounds like I need to investigate the safety brake instead. (While I did work the safety brake on/off a few times, it had no effect on the situation.) Perhaps the safety brake mechanism is broken. The sprocket/drum/chain is not free to move at all, with the motor off or running. (I took the bar/chain off to test with the motor running). I'll have to pull it apart further tonight.
    Debris in the blade can also bind a chain to the point it won't turn. If you haven't done so, back off the chain tightener and see if you can pull the chain by hand. If necessary, remove the chain and use a small wire or knife edge to clean the groove. If it's sprocket nose bar you may have to use brake cleaner to clean the sprocket- be sure and grease it afterward.

    If the bar is clean then I'd suspect sawdust, chips etc. may be binding the safety brake. First step would be to clean everything up with an air nozzle, (use eye protection). and then see what it looks like. If the brake is binding, it may be difficult to remove that assembly. I don't know if there is an external adjustment on the brake but if so, you may have to back off enough to be able to remove it.

    If you have the bar, chain and brake assembly off you can easily see if the sprocket is turning. The inside part of the drum should move when you pull the starting rope. The outside should be free to spin by hand. It's only when the engine is turning at speed do the weights "connect" the inside and outside.

    Treefarmer
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    Fulliautomatix's Avatar
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    Quote Originally Posted by Treefarmer View Post
    Debris in the blade can also bind a chain to the point it won't turn. If you haven't done so, back off the chain tightener and see if you can pull the chain by hand. If necessary, remove the chain and use a small wire or knife edge to clean the groove. If it's sprocket nose bar you may have to use brake cleaner to clean the sprocket- be sure and grease it afterward.

    If the bar is clean then I'd suspect sawdust, chips etc. may be binding the safety brake. First step would be to clean everything up with an air nozzle, (use eye protection). and then see what it looks like. If the brake is binding, it may be difficult to remove that assembly. I don't know if there is an external adjustment on the brake but if so, you may have to back off enough to be able to remove it.

    If you have the bar, chain and brake assembly off you can easily see if the sprocket is turning. The inside part of the drum should move when you pull the starting rope. The outside should be free to spin by hand. It's only when the engine is turning at speed do the weights "connect" the inside and outside.

    Treefarmer
    I've had the bar & chain completely off, run the motor, and when I goose the trigger the inner part spins, but the gear doesn't. So that would lend to the theory that there's something going on with the safety brake. Like I said, I'll pull it apart tonight or another night this week and give it a good cleaning and see what's going on in there.
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    Not sure

    Quote Originally Posted by Fulliautomatix View Post
    I've had the bar & chain completely off, run the motor, and when I goose the trigger the inner part spins, but the gear doesn't. So that would lend to the theory that there's something going on with the safety brake. Like I said, I'll pull it apart tonight or another night this week and give it a good cleaning and see what's going on in there.
    I"m not sure about your saw but most of the saws I've worked on had the chain brake as part of the assembly you remove to get the bar off. The 250 may be integral with the engine housing. If so, you should be able to slip a feeler gauge or a sheet of paper between the brake band and the rim of the sprocket. You should actually be able to move the sprocket by light pressure if the brake is off.

    A parts diagram is at https://www.diyspareparts.com/parts/...grams/ms250-c/ . I don't have a 250 so to some extent I'm shooting blind especially since I've owned more Huskys than Stihls.

    Treefarmer
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    Quote Originally Posted by Treefarmer View Post
    Very nice resource, thanks for sharing!

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    Update: I finally got around to stripping this thing down, and "hosed it out" thoroughly with brake cleaner to blast out all the oil & sawdust crud/buildup behind the cover, between the sprocket drum and safety brake band, and basically everywhere in general. Hit it with a bit of spray lube, put it all back together and gave it a rip and it runs great again. First time doing this... things I learned.

    1. The single tool Stihl gives you with the chainsaw is good for adjusting the chain tension, removing cover bolts, pulling the spark plug, and removing the clutch (which is reverse threaded)... all of which you'll need to do to work on the clutch/oil pump/roller bearing.

    2. As mentioned in #1, that the clutch is reverse threaded.(confirming Tomfive's comments in post #4)

    3. You need to keep the engine from turning over to successfully remove the clutch. You do this by pulling the spark plug and feeding something soft (at least not metal) into the chamber while the piston is at the bottom of the stroke. Then when you loosen the clutch, the piston will be unable to cycle, allowing you to get enough torque to remove the clutch.
    3a. My neighbor recommended a piece of rope (which I didn't have)(also confirming Tomfive's comments in post #4)
    3b. I found a video on youtube where a guy used a piece of pneumatic tubing (cloth/rubber) successfully.(I also didn't have)
    3c. I do not recommended using vinyl water hose (surplus from an under sink water filter project) as the piston will easily shear the hose into small pieces and you'll have to spend an inordinate amount of time getting those pieces out of the chamber, not that I have any experience with that.
    3d. Half of a wooden clothes pin was perfect for the job. (At least for the MS250, the clothes pin goes through the plug hole and perfectly out the exhaust port when the piston is at BDC)
    Last edited by Fulliautomatix; 08-01-2017 at 11:15 PM.
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