550XP Flywheel saga

[GuyMo]

So I bought a 550xp from a chap last month. Started but wouldn’t run (ruined piston).

Finally managed to get all the new parts etc and ran it. 
I absolutely loved it. Ran better than any of my other saws, and knocked spots of my 261 which is much newer and in better condition. 
I was using it to rip out a load of Leyland today when it gave a ‘pop’ and died!

I feared the worst and quickly got it onto the bench.

Absolutely no damage to pot/piston/crank etc.

 

However

 

I took off the starter cover, and the flywheel has sheared off from the crankshaft (not damaging it), and the part of the flywheel that fits in the groove on the crank (equivalent to the woodruff key on most) was in little bits.

 

Has anyone had anything similar happen? Any ideas how this could happen?

Freak occurance?

 

Ive ordered a new flywheel, are there anything that I need to be aware of when fitting it? It’s my first Husky that I’ve worked on, and it’s brilliant, far more intuitive and well designed than all of my other Stihl saws.

 

[Dan Maynard]

When you say sheared off, did it just come loose and fall off or has something on the crankshaft broken?

I saw a more or less new MS194T where the flywheel came loose, must have not been locked on the taper properly but of course that just went straight back to the dealer.

[GuyMo]

Sheared, the key on the inside of the flywheel that first the groove on the crankshaft was in small shards when I removed the starter cover.

[spudulike]

The moulded in key can shear during starting if the flywheel isn't torqued down correctly, just make sure both the crankshaft and flywheel jointing surfaces are clean and grease free then I usually crank the locating nut down pretty hard. The only exception is if the flywheel central boss isn't solid and can crack under extreme pressure.

If you do a load of them, you know how hard to torque....I am sure ADW (Mr Torque Wrench) will give you the correct Nm figure!

[Dan Maynard]

But the crankshaft is clean?

Usually with a taper and key like this the key is more for location and the taper should take the drive, hence why people can get away with filing down a key to advance the timing and then locking flywheel onto the taper.

I would think it can't have been locked on properly, either contamination or a small burr or maybe locknut not to specified torque. Should be in contact over the whole taper area.

[GuyMo]

1 minute ago, Dan Maynard said:

But the crankshaft is clean?

Usually with a taper and key like this the key is more for location and the taper should take the drive, hence why people can get away with filing down a key to advance the timing and then locking flywheel onto the taper.

I would think it can't have been locked on properly, either contamination or a small burr or maybe locknut not to specified torque. Should be in contact over the whole taper area.

Cheers! It’s probably some idiot not tightening the nut enough...

[GuyMo]

5 minutes ago, spudulike said:

The moulded in key can shear during starting if the flywheel isn't torqued down correctly, just make sure both the crankshaft and flywheel jointing surfaces are clean and grease free then I usually crank the locating nut down pretty hard. The only exception is if the flywheel central boss isn't solid and can crack under extreme pressure.

If you do a load of them, you know how hard to torque....I am sure ADW (Mr Torque Wrench) will give you the correct Nm figure!

Thanks! Is there any reason why it would work to just fit a new flywheel, presuming the crank etc is ok?

[Stihllymok]

45 minutes ago, GuyMo said:

So I bought a 550xp from a chap last month. Started but wouldn’t run (ruined piston).

Finally managed to get all the new parts etc and ran it. 
I absolutely loved it. Ran better than any of my other saws, and knocked spots of my 261 which is much newer and in better condition. 
I was using it to rip out a load of Leyland today when it gave a ‘pop’ and died!

I feared the worst and quickly got it onto the bench.

Absolutely no damage to pot/piston/crank etc.

 

However

 

I took off the starter cover, and the flywheel has sheared off from the crankshaft (not damaging it), and the part of the flywheel that fits in the groove on the crank (equivalent to the woodruff key on most) was in little bits.

 

Has anyone had anything similar happen? Any ideas how this could happen?

Freak occurance?

 

Ive ordered a new flywheel, are there anything that I need to be aware of when fitting it? It’s my first Husky that I’ve worked on, and it’s brilliant, far more intuitive and well designed than all of my other Stihl saws.

 

Interesting. I'm in exactly the same boat...first Husky starts but won't run so time to open her up. Mind me asking if you used genuine bits or eBay? Thanks.?

[spudulike]

If the failure is just down to the fact the key on the flywheel has broken then as long as the keyway is clean, the crank taper and the flywheel hole is clean and grease free and it is well torqued down, there should be no reason  for it to fail again. Just check the flywheel to coil gap after torqueing it down as it may change a little.

I don't know why the original would have failed, sometimes, excessive use of a rattle gun on the clutch can loosen the flywheel or it may have been taken off at some time and not tightened sufficiently.

[GuyMo]

3 minutes ago, Stihllymok said:

Interesting. I'm in exactly the same boat...first Husky starts but won't run so time to open her up. Mind me asking if you used genuine bits or eBay? Thanks.?

I cleaned up the original pot, bought a new piston (Meteor). I stupidly bought a different carb (recon) before finding out that it needed to be synced to the coil etc. I was unsure with how it would go (as I’m not particularly experienced) so I didn’t want to shell out for the original parts in case I ruined it. I’d heard excellent things about the Meteor pistons and so far it hasn’t disappointed! I’m hoping that once this issue is sorted, then I’ll be able to keep it running well, as the compression/acceleration etc is excellent!