Sheared flywheel key…

[PV Hiker]

If you have a repair shop or supply place nearby, If they have a flywheel in stock you can take yours and match up the shear key and mark the grove with a pen on top. Then use a punch or chisel and punch marks on the top of the flywheel so you always know where the key limits are. Just a thought.

 

[Wood Doctor]

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

I must admit that I once replaced a sheared flywheel key with a chunk of plexiglass that I shaped. I've also used a sector of a steel washer that I cut with a hacksaw. Either worked fine.

 

[Old2stroke]

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?

Most chainsaw have the low rpm (starting speed) set at 8 to 10 degrees before TDC. If the coil has fixed timing, 10 or a bit more is a normal compromise setting. If the coil has a variable timing curve there are a few other concerns, if the timing is set less than 8 degrees, there might not be enough advance for high rpm and if it is set too high it might kickback on the starter when the cord is pulled. Variable timing coils might take some trial and error to get the timing set far enough before TDC to give best power at top rpm and not be so far advanced that it kicks back when trying to start. I have no experience with digital lights. Any old school units should work fine, if you know a mechanic he will probably give you one as they are completely useless on modern car engines. Hopefully someone can tell you if that is a fixed or variable timing coil, only way to find out is to fire up the engine and use the light to see what happens to the timing marks.

 

[Backstage]

It’s a black coil. My understanding is that the older black husqvarna ones are (usually) unlimited, but I don’t fully understand the implications of that.

 

[frank_]

It’s a black coil. My understanding is that the older black husqvarna ones are (usually) unlimited, but I don’t fully understand the implications of that.

no rev limiter, but mapped spark advance probably eh

 

[PV Hiker]

I must admit that I once replaced a sheared flywheel key with a chunk of plexiglass that I shaped. I've also used a sector of a steel washer that I cut with a hacksaw. Either worked fine.

This past year a flywheel molded in place shear key was wiped off. Dremeled it out and cut a piece of poly material to fill it.

 

[Backstage]

This past year a flywheel molded in place shear key was wiped off. Dremeled it out and cut a piece of poly material to fill it.

That might help with future reinstallation once I get the timing set right. I’ll probably end up just making a deep scribe line mark on both the mandrel and flywheel.

So set 8-10 BTDC. Closer to TDC = better rpm, further = harder start but “torquier” feel from what I’m reading elsewhere. Anyone able to confirm that or kick me in the head?

 

[frank_]

That might help with future reinstallation once I get the timing set right. I’ll probably end up just making a deep scribe line mark on both the mandrel and flywheel.

So set 8-10 BTDC. Closer to TDC = better rpm, further = harder start but “torquier” feel from what I’m reading elsewhere. Anyone able to confirm that or kick me in the head?

some husky ignition curves here
https://www.arboristsite.com/threads/husqvarna-timing-curves.249672/

 

[Nex]

To add a piece of advice to all the good stuff above.
Once you've got the flywheel down and test-run and you feel happy with the performance. Loosen that nut again (don't worry, the flywheel won't move) and put a dab of 2 component epoxy in the threads and re-tighten as hard as you dare. Those nuts have a tendency to back them self off almost no-matter-what.

The flywheel doesn't have to come off that often, and when it does it's a minor thing to break out the propane-torch to get it off.

 

[Old2stroke]

That might help with future reinstallation once I get the timing set right. I’ll probably end up just making a deep scribe line mark on both the mandrel and flywheel.

So set 8-10 BTDC. Closer to TDC = better rpm, further = harder start but “torquier” feel from what I’m reading elsewhere. Anyone able to confirm that or kick me in the head?

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?

Here is some info that might be helpful when your timing light comes.
CHECK IGNITION TIMING WITH A TIMING LIGHT
For these tests, it help to stabilize the saw by removing the clutch side cover and the chain, tighten the bar to the saw with a couple of spacers and the bar nuts, then clamp the bar in a bench vise.
JUST A SIMPLE CHECK To check the basic timing at low rpm, you remove the plug and externally ground it to the cylinder, connect the light sensor to the plug lead and ground the lights' power supply to the cylinder (you need a 12 volt power supply for the light). After finding TDC, you make a mark on the FW and a corresponding mark on the engine case, you then drive the engine by connecting a reversible variable speed drill to the FW nut and start rotating it in the right direction. Just turn it fast enough for the light to flash and strobe your marks, you can see where the spark occurs and use some geometry to work out the firing relative to TDC. Spray some WD40 or light oil in the plug hole to lub the piston a bit and don't try for higher rpm than necessary. This just checks the current timing, if you want to modify it, you have to go to the clutch side and use a timing wheel or similar device to reference everything to the actual crankshaft and not the FW because once you rotate the FW on the crank, your FW mark will no longer represent TDC. Remember this is being done at low rpm where all you are doing is checking basic timing and if you have a variable timing coil, it is subject to change as the electronics in the coil varies the timing with rpm. Checking the timing at high rpm is different as you have to fire up the engine and watch the timing change as you bring the rpm up.

CHECK WHEN MODIFYING THE TIMING
Always check the original timing before making any changes so you will know how much change you are getting. If you want to advance the timing, you shave a bit off the key that will allow you to rotate the FW counter clockwise with respect to the crank. Generally, shaving 0.010" off the key will produce about 5 degrees of change, depending on the diameter of the crank.

HIGH RPM CHECK
With a vertical cylinder engine you will probably have to do this with the top cover off so you want to avoid over heating the engine by not running the engine longer than necessary for a quick test.

TIMING LIGHT: Some lights will not flash consistently unless the negative end of the power supply is grounded to the cylinder of the saw. A good power supply is an AC adapter, 110volt to 12volt DC that can supply 500ma.

FINDING TDC: With the piston at TDC, there is a flat spot where you can rotate the FW in either direction a few degrees with no apparent movement of the piston, so you need a fairly accurate way to find true TDC. Remove the muffler, bring the piston to TDC and set the pointer on the degree wheel to zero (TDC). Clean a spot on the piston that you can see through the exhaust port and make a mark on it with a black ink sharpie then rotate the engine until the mark lines up with the bottom of the exhaust port and note where the pointer is on the wheel. Now rotate the engine in the opposite direction until the mark lines up again in the same place and note where the pointer is again. The center of the 2 readings will give you the true TDC, so rotate the engine to that reading and hold it still while you re-zero the wheel.

DEGREE WHEEL: Since you are only checking ignition and not ports opening and closing, you don't need a complete degree wheel, just degree markings to 20 degrees both side of zero. Easy to make with a circle of white cardboard that will fit in the housing and a protractor to do the marks. The usual way to mount it on the crankshaft is to remove the clutch and clamp the chuck out of an electric drill onto the crank, then use a spacer, couple of washers and a nut to secure the wheel to the threaded end of the chuck. A pointer can be made from a bent piece of stiff wire clamped to the cylinder with long-nose vise grips. Another way to mount it is to get a 1" long piece of 1" wood dowel and drill a hole through it that is the right size to let it slip on the crank, attach the wheel to one end and use a saw to cut 2 slits at right angles to each other on the other end. A hose clamp on the slotted end will tighten it on the crank.

 

[Backstage]

That got me up and running. Thanks all! For future readers, the condensed version that worked for me is as follows:

BASIC CHAINSAW TIMING

With the clutch cover, bar/chain, muffler, recoil panel, the black plastic air baffle thing, and spark plug removed. Also remove clutch, plastic oiler gear. Maybe zip tie your wires out of the way so they don’t get wrecked.

Tools needed:
Timing light (basic is fine), 12v battery, ie a charged car battery
normal hand drill with 13mm socket driver
torque wrench set to 25 foot pounds with 13mm driver
Scrench (chainsaw tool)
tools to remove clutch
plastic, rubber, or wood hammer
sturdy piece of plastic to block piston
digital calipers
sharpie marker and alcohol wipe to remove marks
some copper wire or similar
red loctite

Put a bit of 2 cycle oil or similar to lubricate piston and other moving parts in through muffler port or wherever. Try to get a little down the transfer ports.

Cut a nice circle about 3.25” diameter (just larger than the clutch) out of cardboard, stiff paper etc. Mark center and make hole about 3/8”. Install under the clutch. block piston through muffler port with your plastic piece and tighten clutch. The clutch acts like a nut holding the cardboard tight. This is your timing wheel. Mount wire so it points to any spot on the wheel.

Find top dead center with digital caliper down spark plug hole by rotating crank. Mark the spot on the wheel where the wire is pointing at TDC.

Mount timing light to spark plug wire (plug is attached and threaded in). Power light, point at your “timing wheel” and use drill to drive the flywheel nut counter clockwise (drill in reverse). This is Foreward for the crank. Go as slow as you can to make the timing light flash.

Observe the degree difference between your mark during the timing light flash, and your wire pointer. That’s how far off you are. It will change as you increase speed, but you’re interested in the slowest speed the spark plug will fire at. The coil automatically advances as the RPMs increase, don’t worry about that unless you know better for some reason.

Mark the flywheel and case with a sharpie or something removable so you know where they were. With piston blocked, remove the flywheel. You probably need to tap it with the soft hammer to loosen it. reinstall at the degree offset you observed in the last step. When reinstalling the flywheel, just hand tighten with a scrench or socket driver. You only need it to be just tight enough not to move from the drill.

Recheck and repeat until correct. If your degrees get worse, you’re going the wrong way.

When it’s right and the mark disappears under your wire when viewed with the timing light, mark your flywheel/case so you don’t loose the position. Remove the flywheel nut. Add red (permanent) locktite to the threads. Replace flywheel nut. Torque to 25 foot pounds.

Reinstall all the parts you removed from the saw. Done!

 

[heimannm]

The static timing on all of the old McCulloch saws was 26 degrees BTDC, if you only go for 8-10 degrees BTDC you will be retarded on timing and performance will suffer.

Mark

 

[Backstage]

You’re just setting initial low (pull start speed) rpms here with a variable coil. I actually cross checked this with a couple other stock saws. The min rpm spark goes exactly tdc, and the coil does the rest. Yes, manually advancing further can change the characteristics, but that’s not what I’m looking for personally.

 

[Backstage]

It could also be worth the time for those worried about it to use the timing light to observe advance at cutting rpms.

 

[Old2stroke]

(plug is attached and threaded in

Why do this with the plug in? You are just putting more load on the drill by making it turn through compression.

 

[Backstage]

Good catch!

Forgot to mention I had the decompress removed. It was the easiest was to make electric connection and my timing light wasn’t going off without that.