Stihl MS 390 carnage - disassembly.

[stihltech]

Looks like a plastic bearing cage failed. Good thing about them, the piston and cylinder tend to survive.

 

[MacAttack]

Looks like a plastic bearing cage failed. Good thing about them, the piston and cylinder tend to survive.

I hope you're right!

 

[Pioneer]

An improperly tightened flywheel will shear the key. Your old one will still be good, just index it and tighten it properly. The keyway is only there to ensure proper ignition timing.

I've seen saws eat the main bearings because of pre-ignition. There were telltale signs on top of the pistons. I've done a 290 rebuilt with a 390 kit, even then I considered it underpowered for its weight. Kind of a goofy muffler mounting system on it, doesn't allow for an easy muffler mod.

That being said, parts are readily available and although there are some difficulties in assembly, it's not the worst saw to practice on.

 

[MacAttack]

An improperly tightened flywheel will shear the key. Your old one will still be good, just index it and tighten it properly. The keyway is only there to ensure proper ignition timing.

I've seen saws eat the main bearings because of pre-ignition. There were telltale signs on top of the pistons. I've done a 290 rebuilt with a 390 kit, even then I considered it underpowered for its weight. Kind of a goofy muffler mounting system on it, doesn't allow for an easy muffler mod.

That being said, parts are readily available and although there are some difficulties in assembly, it's not the worst saw to practice on.

Thanks for the input!

I don't need a high performance saw...if it ends up a runner I'll be happy.

I'm going to try and remove the bits of trashed key from the flywheel with a dremel.

 

[Bob Hedgecutter]

Thanks for the input!

I don't need a high performance saw...if it ends up a runner I'll be happy.

I'm going to try and remove the bits of trashed key from the flywheel with a dremel.

Should drive out with a pin punch- then if you are not going to re key- lap the flywheel to the crankshaft with some lapping/grinding paste- there is a lot of galling on the taper bore of your flywheel, clean it up a bit- clean off all the lapping compound, index it to original position and tighten the nut down well.