Sheared flywheel key…

[Backstage]

Putting a husqv 455 together, I apparently didn’t get the flywheel nut tight enough and it sheared the molded in key. Is this salvagable? It looks like I should be good with very tight torque on the nut? Also trying to get the timing lined back up. At Bottom Dead Center, the magnet on the flywheel is supposed to be centered on the big protrusion on the ignition module?

Having fun with this saw. But any help here would be appreciated.

 

[Binthewoods]

The key isn’t important if you get the flywheel torqued down in the correct position. Make sure the flywheel and crank are degreased.

 

[Jasent]

Use a sharpie all the way up the shaft and threads to mark the groove and mark fw. Easy peasy. Might take this time to advance timing a hair see how ya like it

 

[frank_]

i usually needle file a groove where the key used to be, and than hammer a dowel down the hole
and i always tighten down the nut, and then smack the top of the socket to make sure the flywheel is home,
then i recheck the torque

 

[cgeb]

Just a mark really use the sharpie to mark and torque the nut back down. Stihl dealer told my BIL his saw was toast with a sheared key. I marked it and torqued it runs like a champ. BIL found a new dealer.

 

[Old2stroke]

Be nice if someone could give you a torque setting for the nut, like most, I just rely on experience and don't have a clue as to how much torque I'm using. It has to be TIGHT but without the risk of damaging the crank threads.

 

[Backstage]

So the cast in “key“ is just an alignment guide. Got it. Exceptionally helpful, and this part is over $100 so that’s good news!

Some more digging reveals we want about 25 foot pounds torque, but I have yet to dig through the 455 workshop manual to see if it’s listed there.

The problem still though is that the key is sheared so clean it’s hard to be 100% sure exactly where it was. Where exactly do I locate this with relation to the stroke?

 

[K-techcowboy]

Putting a husqv 455 together, I apparently didn’t get the flywheel nut tight enough and it sheared the molded in key. Is this salvagable? It looks like I should be good with very tight torque on the nut? Also trying to get the timing lined back up. At Bottom Dead Center, the magnet on the flywheel is supposed to be centered on the big protrusion on the ignition module?

Having fun with this saw. But any help here would be appreciated.

I did the same thing with a cheap ass flywheel off ebay for my ms 250. I went to atwoods(a bigger tractor supply type store)where in there hardware section they sell many different size keys and bought 3 different sizes. Then where the old one was made in the flywheel I cut a slot with a dremal for the correct size key to slide in and wala your done.

 

[Backstage]

Yeah, the problem with the way Husqvarna does things is that the "key" is actually a nub in the casting. There is no key slot. There's no longer a physical record of where it should go if it shears off cleanly enough.

 

[frank_]

Yeah, the problem with the way Husqvarna does things is that the "key" is actually a nub in the casting. There is no key slot. There's no longer a physical record of where it should go if it shears off cleanly enough.

you may need an oldschool timing light then

 

[Jasent]

Magnet should line up with coil just before top dead center

 

[Backstage]

Thanks, that’s an extremely useful reply!

Okay, so I wasn’t COMPLETELY honest. It’s a darn clean shear. Insidiously nearly polish work. Seriously, Lady Chaos doesn’t usually do such tidy work.

But she still left what looks like it MIGHT be the remains of a shear point, and that lines the flywheel up so the magnet’s leading edge is just about lined up with the far side of the coil at TDC.

How correct does that sound? Seems with that alignment, the plug should be starting firing just before TDC, which about right?

 

[Old2stroke]

Most of those molded-in keys have some indented marks on either side of the key, if your has any, you should be able to find the center of them and use that to line up with the center of the keyway slot. You are right about where the FW magnets should be relative to the coil, but you could easily be off by more than 5 degrees.

 

[Backstage]

Some kind of factory mark was the first thing I looked for. No luck.

Here’s a photo of the magnet/coil positioning at exactly tdc. Green lines added outside the magnet (Magnet fully within the lines) on the flywheel for clarity. It’s surprisingly hard to photograph this without depth perception.

 

[Tobystihl]

Be nice if someone could give you a torque setting for the nut, like most, I just rely on experience and don't have a clue as to how much torque I'm using. It has to be TIGHT but without the risk of damaging the crank threads.

Be nice if someone could give you a torque setting for the nut, like most, I just rely on experience and don't have a clue as to how much torque I'm using. It has to be TIGHT but without the risk of damaging the crank threads.

I give it a couple of ugga dugga's with the windy....

 

[mbrick]

The torque spec on my 576 is 35Nm or ~26 ft lb.
I had this exact same issue happen. Except it took me a long time to figure out why it ran like crap.

I temporarily located it by eye and tightened it down and it ran well but later ended up buying a used flywheel because I could not get it accurate within a few degrees (that I was confident to).
It is surprisingly hard to translate a sharpie mark onto the front. And then once the flywheel is slid on you can not see the keyway.

 

[frank_]

Some kind of factory mark was the first thing I looked for. No luck.

Here’s a photo of the magnet/coil positioning at exactly tdc. Green lines added outside the magnet (Magnet fully within the lines) on the flywheel for clarity. It’s surprisingly hard to photograph this without depth perception.View attachment 947238

looks way too late to me, the electronic coils need a lot of dwell, so that it can hold back the spark at low rpm
without a timing light and reversible drill, you are just making a wild guess

 

[Old2stroke]

As mentioned, the only way to accurately locate the FW is to do it with a timing light and a segment of a degree wheel. You will need a reversible variable speed drill and a timing light that will probably require a 12volt power source. The clutch has to be removed and a degree wheel (easy to make) attached to the crank, then you have to locate the piston to TDC and place a pointer on the wheel. By using the location of the FW magnets and the coil, mount the FW on the crank as a "best guess" to where it should be. Next you have to remove the plug and ground the base to the cylinder with a test lead, squirt some WD40 or light oil in to give the p/cyl some lub, hook up the timing light and use the drill attached to the nut on the FW to rotate the engine in the proper direction (ignition ON). Just bring the engine speed up until the light flashes and strobe the degree wheel (if the FW nut comes off, it wasn't tight enough). The strobed mark on the degree wheel will tell you where the spark is now occurring and you can use that to adjust it to where it should be. Not as difficult as it sounds and if you want to pursue it, I can provide better details.

 

[Backstage]

That sounds straightforward up to the point where you can see where the spark is happening on the rotation/stroke. I still don’t have my head fully around the “where it should be” part. Is that spark supposed to be happening at exactly TDC, a degree or five before etc?

Looks like I’m sourcing a timing light. I see there’s some used old school Snap-On ones reasonably on eBay. Any reason to get a new digital type one? Advance settings should be on zero for this job?

 

[frank_]

That sounds straightforward up to the point where you can see where the spark is happening on the rotation/stroke. I still don’t have my head fully around the “where it should be” part. Is that spark supposed to be happening at exactly TDC, a degree or five before etc?

Looks like I’m sourcing a timing light. I see there’s some used old school Snap-On ones reasonably on eBay. Any reason to get a new digital type one? Advance settings should be on zero for this job?

timing at starting speed should be tdc ish, so a marker pen on the flywheel and casing
then as you speed the drill up it will move btdc (25ish)