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Fan was so tight on the crankshaft that the piston stop put a hole in the top of the piston. Took a 2ft long breaker bar and a lot of a$$ to break it loose.

I have been coming across a lot of chainsaws lately that they are installing the clutches with red loctite and need to use a small torch to warm the clutch in order to break them lose from the crankshafts. So is it possible they used loctite on the fan threads.

These fans naturally tighten over an long period of use.

From the service manual...

Right-hand thread. Very high
release torques may be necessary
after long periods of operation.

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Should just use an impact to spin off the fan after you remove the recoil but leave the spark plug in for compression loading. Using a breaker bar and piston stop is just asking for a hole in the piston. I nearly did the same here several years ago but I tried the impact which like charm.

When installing the fan use no lube and torque to 22 ft/lbs (264 in/lbs). Now this where you will the piston stop. Even then 22 ft/lbs is a lot to bear by the piston.

I tried the impact on the fan nut once. Broke the nut out of the plastic fan. Proline AM piston only $38 so not a disaster

Maybe I have a lighter touch or maybe I just got lucky

Same problem here
I warm the fan nut
Apply penetrant allow to cool heat it up again spray penetrant allow it to cool , repeat many times
Try rattle gun if no joy back to the heating cycle .
Local Stihl shop says they cut the fans off & charge customer for new fan
And yes they really do self tighten a massive amount .

Boy did I have my screwed on wrong on this one after a few restless nights I went to my hand written notes. Hammer your are right about using a pull bar the remove. My notes suggest the fan wheel takes too much inertial to get started with the impact and a pull bar is the way to go.

Boy do I feel like an idiot right now but I admit I was wrong on this one. I reckon I can blame it on old age.

StarTech said:

Boy did I have my screwed on wrong on this one after a few restless nights I went to my hand written notes. Hammer your are right about using a pull bar the remove. My notes suggest the fan wheel takes too much inertial to get started with the impact and a pull bar is the way to go.

Boy do I feel like an idiot right now but I admit I was wrong on this one. I reckon I can blame it on old age.

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Haha. I've never made a mistake. Well, at least not in the last 5 minutes. I had the blower engine completely apart 6 times trying to figure out why it had low compression. Not until I really cleaned the carbon off the top of the piston did I realize it had a hole in it. The blower would almost start with the hole in the piston.

The impact doesn't do much, I had to buy the Stihl piston stop and use a wrench/bar.
Otherwise I use the impact.

I don;t like using piston stops as to me they can put too much pressure on one small area. I keep a clean length of paracord to use as a piston stop.
MY PISTON STOP IS BETTER THAN YOUR PISTON STOP

Scrubcadet10 said:

I don;t like using piston stops as to me they can put too much pressure on one small area. I keep a clean length of paracord to use as a piston stop.
MY PISTON STOP IS BETTER THAN YOUR PISTON STOP

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I have some of the plastic stops and have used the starter rope trick. I read on another forum that people have damaged the thin valves on the 4mix engines using the rope trick so I bought the piston stop.
MY PISTON STOP IS BETTER THAN YOUR PISTON STOP.

I tried some aftermarket plastic piston stops and they failed to work. Just trashed them and brought the metal ones. And I holed a couple pistons myself on chainsaws here using piston stops. Just one of the hazards using them.

Hammermechanicman said:

I have some of the plastic stops and have used the starter rope trick. I read on another forum that people have damaged the thin valves on the 4mix engines using the rope trick so I bought the piston stop.
MY PISTON STOP IS BETTER THAN YOUR PISTON STOP.

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I use plastic ones so they will bend rather than hole the piston .

Taking off one of these fanwheels is something you need to do, to see what it takes.

Fish said:

Taking off one of these fanwheels is something you need to do, to see what it takes.

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Yes sir! I had to set the engine block between the jaws on my big vise and use a 2' bar and a lot of muscle to get it loose. And ruin a piston.

On other equipment needing a piston stop, I've used water, simply putting it in the cylinder and putting the plug back in. When done, just pull the engine over a few times to blow out the water. Used this many times before I heard about using rope. From that time on, I just called it the "Rope A Dope Piston Stop" Never had a problem with either method, but using the rope was easier and quicker.

Hammermechanicman said:

Fan was so tight on the crankshaft that the piston stop put a hole in the top of the piston. Took a 2ft long breaker bar and a lot of a$$ to break it loose. View attachment 66817

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Small diameter nylon rope....stuff a couple of feet in through the plug hole.The pointy end of a stop just doesn't cut it for me....

That is why you need to buy their piston stop and follow their procedure.

I used their locking screw and still damaged the piston. Oh well, just a hack with some shiny tools.

Hammermechanicman said:

I used their locking screw and still damaged the piston. Oh well, just a hack with some shiny tools.

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You used that same tool? #4180 890 2700?

Copy but looks just like it

Hammermechanicman said:

I used their locking screw and still damaged the piston. Oh well, just a hack with some shiny tools.

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Rope in the hole..... Works every time but then you risk connecting rod damage if overly aggressive.

Not sure if true or not but in another forum a guy said he damaged a valve using the rope method. I didn't want to risk it.

Hammermechanicman said:

Not sure if true or not but in another forum a guy said he damaged a valve using the rope method. I didn't want to risk it.

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Well....if you insist on putting it in with the valves open you deserve the grief.

Nothing is 100% safe. As mechanic we all should know things can go awry at the least most opportune time.

I wonder how many people on here have used the rope method piston stop on a 4mix stihl backpack blower? You can't take the cam cover off so you either have to back the rockers way off or get just enough rope in the cylinder that when you crank about 75ft/lb on the fan nut that the valves aren't open.

Hammermechanicman said:

I wonder how many people on here have used the rope method piston stop on a 4mix stihl backpack blower? You can't take the cam cover off so you either have to back the rockers way off or get just enough rope in the cylinder that when you crank about 75ft/lb on the fan nut that the valves aren't open.

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Valves are never open at TDC of the compression stroke and the rope is fed in just before it gets there. Two strokes are so much easier.....