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I'm at a loss.. please help.. Stihl FS450

MagraAdam

MagraAdam

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Hi guys,

So i got a second hand FS450.. love it! heaps of power and great to use.. then the shaft rounds, so i get a new shaft.. it's amazing again! then the bearings in the con rod go, so i order a new crank shaft/con rod and a new cylinder and piston kit. I fit these all up and she won't start at all. I realise that the carby is one of the old fixed jet ones, so i order a new carby too and fit that. It still won't start. it has compression. it has spark. it has air. the fuel primes through the bulb, the filters are all clean. if i put some fuel in the cylinder i can get it to spark a few times, and using some starter spray i can get the same, but it just doesn't run. I have the same symptoms with both carbies. I have tried the adjustable one at 1.25 turns on both screws as instructed on one of the videos i watched, but it isn't just out of tune, it won't start. the old carbie that just had the idle adjustment (the venturi screw i believe) has been set to every possible position and all the same.. a couple of ignitions at best then nothing. I have checked all the hoses and they all don't have any holes.

So.. any help would be amazing, as i'd love to get the beast back up and running.

Thanks heaps!


Adam
 
MagraAdam

MagraAdam

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Is the flywheel matched to the coil and correctly fitted to the crank so the timing is correct?
did the flywheel shear the key, and move, thus sparking at the wrong time ?

only thing I can offer at the moment.
Mate you seem to be 100% right, I did manage to break the key.. Weird that it was igniting a bit, but i guess the timing was out. Now to find a replacement part.. seems like it's a weird model to get parts for unfortunately..
 
frank_

frank_

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Mate you seem to be 100% right, I did manage to break the key.. Weird that it was igniting a bit, but i guess the timing was out. Now to find a replacement part.. seems like it's a weird model to get parts for unfortunately..
i usually cut a small slot where the keyway was , then fit the f/w by eye, and then drill down and drive a thin rod down the hole
 
John Lyngdal

John Lyngdal

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I think the newer FS480 uses the same flywheel. I sheared a key in my 056 chainsaw and all I had to do was replace the key, the flywheel was fine.
Is your flywheel or crankshaft damaged? It might it be repaired just by installing a new key?
 
trains

trains

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Mate you seem to be 100% right, I did manage to break the key.. Weird that it was igniting a bit, but i guess the timing was out. Now to find a replacement part.. seems like it's a weird model to get parts for unfortunately..
its the taper that holds the torque of the flywheel, not the key, that only indexes it correctly when you assemble it.
So clean up the taper, make sure its clean of oil etc, same with flywheel, fit in correct position, give it a gentle seating tap with long socket, then torque up to spec, and run it.
 
MagraAdam

MagraAdam

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I think the newer FS480 uses the same flywheel. I sheared a key in my 056 chainsaw and all I had to do was replace the key, the flywheel was fine.
Is your flywheel or crankshaft damaged? It might it be repaired just by installing a new key?
The key is cast into the flywheel unfortunately.. well.. it was..
 
MagraAdam

MagraAdam

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its the taper that holds the torque of the flywheel, not the key, that only indexes it correctly when you assemble it.
So clean up the taper, make sure its clean of oil etc, same with flywheel, fit in correct position, give it a gentle seating tap with long socket, then torque up to spec, and run it.
Thanks mate, I'll give that a try
 
MagraAdam

MagraAdam

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i usually cut a small slot where the keyway was , then fit the f/w by eye, and then drill down and drive a thin rod down the hole

can you dremel down the old key into a slot to fit a section of keystock bar?
I was thinking about trying something like this. Anyone know what size key stock I need? Or a good supplier in Australia for stock?
 
MagraAdam

MagraAdam

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4134 is a completely different model class than 4128 series
G'day mate, I thought that would be the case. Interestingly I just found this that seems to imply these models all use the same flywheel?

 
frank_

frank_

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I was thinking about trying something like this. Anyone know what size key stock I need? Or a good supplier in Australia for stock?
you only need a sawblade notch to line it up, then i use a 3mm drill down the keyway on the mowers that i do it to (they have a shearkey to prevent the crank bending) but yours probably needs a 2mm drill and then just drive a nail down the hole, and cut the excess off the top
 
cookies

cookies

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measure the keyslot in the crank, any small engine shop or hardware store worth a hoot will have key stock rod, if they have the wrong size buy the next size up to have the ability to grind it down to size. Like another member stated the flywheel is held in place by the tapers on the crank and bore in the flywheel press fitting and the key aligns them...you could even use a square wooden or aluminum dowel, the reason i suggested keystock is it is generally the same fractional sizes across all manufacturers. You could even draw alignment lines on the crank and flywheel to install without the key but beware of misalignment and shifting during tightening.
 
MagraAdam

MagraAdam

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Ok, so I finally got around to making a key out of aluminium after I found my small files and modified one of them to file a square hole in the flywheel. Both tuning screws are set to 1.25 turns and I put fresh help in it. Exactly the same as before. I can get it to turn over a few times using starter spray, but that's it.

Any other thoughts before I have to pay someone to look at it? (At which point I will have spent more fixing it than I did buying it..)
 
bcorradi

bcorradi

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I think I have a new or like new fs450 powerhead. I got it in a lot of parts at a state auction. To be honest with you, I'm not sure if it ever had gas in it. It appears parts were just scavenged off of it. Send me a msg if you would like more information.
 
Bobby Kirbos

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Don't pay for labor. There is more available knowlege on this site than you will find at a single repair shop. There are guys here who have brought saws back from the grave.


Throw a tablespoon of mix down the carb. You'll likely get a bit more run time from that then you get from starter spray. The slightly longer run time will give you a better indication of whether or not the timing is correct (which it most likely is).

It does sound to me like you have a fuel delivery problem at this point.
 
MagraAdam

MagraAdam

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I think I have a new or like new fs450 powerhead. I got it in a lot of parts at a state auction. To be honest with you, I'm not sure if it ever had gas in it. It appears parts were just scavenged off of it. Send me a msg if you would like more information.
Thanks heaps for the offer - I'm pretty sure shipping to Australia will be cost prohibitive. I've also replaced the shaft, the gear box, the carby, the cylinder, the piston, the crack shaft and con rod, the bearings. by now i may as well have bought a new one :/
 
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