So i've been using a poulan pro 4218 all summer, ran like a champ for me everyday all day. then the crankshaft holding the clutch and sprocket snapped.. not a problem bought the part and replaced it. i cleaned every part woth carb & part cleaner before rebuilding anything. put it all back together very carefully and how i had taken it apart.. the saw started and the chain ran. it would top out and almost back to normal.. but it won't idle it turns off as soon as the revs go down. i'm completly lost

Remove the clutch hub and sprocket, then using a Poulan clutch tool, unscrew the clutch assembly and replace.

YES IF SAME MODEL AND SIZE, MAY BE IT WORKING PULL OUT THE DEFECTIVE ONCE AND REPLACE OR SWAPPING BY THE OTHERS SAME IN SIZE AND MODEL. I THINK ITS GUARANNTY WORKING..

sorry but from what I am seeing and reading, the clutch screws onto the crankshaft then the clutch drum slides onto the crankshaft and an E clip holds it in place... if that rod is broken this means your crankshaft is broken meaning throw it away

I have referenced the Poulan Pro 4218 Manual so you can see a similar troubleshooting guide which should be close to the 4620 version.

4218 is the model, the key is part of the flywheel, so if the key has sheared it will require a new flywheel.

Most oil pumps are situated behind the clutch and sprocket, these will need to be removed before you can acsess the old pump, if it has an inboard sprocket you will need to remove the clutch first, these are a left hand thread and just spun onto the crankshaft, they need to be jarred off against the compression of the saw, you may need a special tool if there is no nut on the outside of the clutch, this tool fits most Poulon clutches 530035560, once removed it is a fairly straight forward job to change the pump.

Try the easy solution first and post back if this does not solve the problem:

Insure your chain is on the teeth of centrifugal clutch sprocket correctly. It is easy to have it either on the inside of the sprocket or on the outside of the sprocket. If it is not on the sprocket teeth, it will not turn the chain.

New Saw? Warranty time
Electronic ignition? Replace entire module. Pinched wire to metal case part for ignition switch. Permanently shorted ignition switch--replace.

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my name is Dennis Gladx and I can assist you with the problem of getting the sprocket off of the crankshaft of your chainsaw.

To remove the centrifugal clutch and sprocket you unscrew it from the crankshaft and it has a left hand thread. Also a little trick to remove anything from a crankshaft that could turn while you want to unscrew the item, Remove the spark plug and insert some rope into the cylinder for the piston to squeeze against and you will jam the piston without damage.

Glad to be of assistance Please rate this solution because I can learn from your rating. Thank you

If you mean the teeth on the chain, then you would not need to remove the clutch to change it.
Presumably you mean the drive sprocket is worn.
To do this, you need to stop the engine from turning over while you undo the nut.
You should have got a piston stop with the saw. Funny little flat plastic thing with round ends. You probably wondered what on earth it was for (I did). If you've not got it, you can improvise.
You remove the spark plug & insert one end of the tool, basically, this puts a lump of hard plastic on top of the piston so it cannot reach the top of its stroke.
This means you can undo the nut holding the clutch & sprocket to the crankshaft.
It will be left hand thread (I'm fairly sure).
Should be easy from there, but come back if you're still stuck.