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Stihl MS261 no spark

Started by buckwheat1, November 06, 2017, 07:25:57 AM

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buckwheat1

Hello to everyone on the forum and thanks for letting me join. I have a MS261 in the shop with no spark. I've changed the coil out with a Stihl OEM coil The flywheel has 2 magnets(on opposite sides)with on side being a little stronger than the other side. BTW, it's not an Mtronic. It came in with the complaint that it started to sputter then quit running. Customer wasn't able to restart. I pulled on it a few times and no spark. Changed the plug-still no spark. I found the flywheel to have a sheared key which would certainly lead to the original complaint but can't figure why I can't get it to fire. The saw should fire with the flywheel spinning even if the timing's off. New coil set with a plain business card at first. I then tried it closer and farther away. Has anyone ever had a flywheel cause a no spark problem? Looking forward to hearing some ideas. I appreciate any suggestions. Thanks

buckwheat1

Sorry I forgot to add that I also disconnected the switch wires from the coil to eliminate that. Thanks, Buckwheat1

Hilltop366

Did you reuse the plug cap and/or plug wire?

buckwheat1

There is a new wire and cap molded into the coil. Thanks for the reply.

Hilltop366

Did you try a known good plug, sometimes a new one is no good.

buckwheat1

Tried new resistor and non resistor plugs plus one from a running saw. This saw's really a corker. Thanks for the replies.

teakwood

Wait till joe_indi chimes in or write him a PM, he is "the man" for these problems
National Stihl Timbersports Champion Costa Rica 2018

Texas-Jim

You are correct, it will fire regardless on the flywheel timing. There are about 9 models of that saw, do you know which model it is?
What we do in life echoes through eternity.

buckwheat1

The recoil cover just says MS261- no C or CM. It has the standard jet adjustments on the carb with no other wiring other than the wires to the switch.

buckwheat1

Pulled the flywheel and found the N & S poles are correct on the magnets that fire the plug. Opposite these magnets are another set that seem to have little or no magnetism-they won't grip a small and light piece of wire. What are these extra magnets there for?

sawguy21

Those are counter weights to offset the magnets and allow the flywheel to be balanced.
old age and treachery will always overcome youth and enthusiasm

sawslinger

I have this same problem. I hope someone posts an answer so I can stop banging my head against the wall.

Chefblair

Make sure the new coil is good by measuring resistance with multimer and comparing to manufactured specs. Usually around 225 ohms. 

Mad Professor

Does the coil itself have continuity to the cylinder?  That is coil body where it bolts up.

farmfromkansas

Had to replace the flywheel on a lawnmower engine once, had no spark, magnet must have been weak.
Most everything I enjoy doing turns out to be work

joe_indi

Quote from: teakwood on November 06, 2017, 07:20:42 PM
Wait till joe_indi chimes in or write him a PM, he is "the man" for these problems
Oh No! :o I never saw this thread until today.
OK teakwood, let me see if I can live up to your expectations ;D

buckwheat1, though this post might be too late for you (its just short of a month since your original post), maybe I can give you some pointers that might be useful, to you or to others.
Shearing of the flywheel key changes the ignition timing. In the case of a molded key in the flywheel, it is not necessary to throw away an otherwise perfect flywheel just because the key has sheared off. On the Stihl saws, the key only aids to align the flywheel and crankshaft. The tight fit is ensured by the tapered faces on the crankshaft and flywheel.
All you have to do is mark the position of the groove (on the crankshaft) and the position of the sheared flywheel (on the flywheel) on the outer side, to make it visible to you. Apply a little bit of threadloc on the crankshaft (a very little bit) and with the saw on its side lower the flywheel onto the crankshaft with your marks in alignment. Doing this with the piston at the bottom makes things easier since the magnet could keep getting pulled towards the coil.
Once you have the flywheel fully lowered, fit the nut with your fingers till it locks. Use a plug spanner over the nut to tap the flywheel onto the crankshaft more. When it goes down a bit the nut will turn in a little bit more.
Now, lock the piston and use a wrench to tighten the nut to its maximum.
The flywheel will now be tight with the correct ignition timing.
Dont connect the switch wire yet. Not until you have tested whether the ignition works

I would suggest you remove the carb, prime the engine with a few drops of fuel down the inlet manifold . Try firing the saw up. If things are fine (upto this point) after a couple of pulls the saw should start up, rev and then die.
Next, try it once more, but with the switch wire connected. If it still starts up, try it next with the carb fitted.

I hope all this helps someone. Even yesterday I used this method on a FS131 with a sheared flywheel key. One of the early fixes on a 036 is still fine after 5 years.
Good Luck
Joe

Mad Professor

You are NOT supposed to use anything on Stihl flywheel tapers, not threadlock, not grease, not oil.

If you spun the flywheel you can lap the damaged wheel to the crankshaft using some valve grinding compound.  You will end up with a perfect fit.  Be sure to clean all the compound off the flywheel and crank, it will destroy the seals if you don't and interfere withe the fit.

The keyway is just to align the  flywheel, what holds the wheel is the taper fit and the nut. 

If you want to play with timing you can file the keyway a bit to move timing a few degrees.

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