Small Engines (Lawn Mowers, etc.): Stihl 029 Chainsaw Starting Problems, piston damage, spark arrester

Question
My Stihl 029 chainsaw has extremely strong backpressure on starting.  So much so that the starter handle is pulled out of my hands while attempting to start.  I've replaced air and fuel filter, as well as spark plug.  I've also cleaned the muffler and spark arrester.

With the spark plug removed the piston moves easily in the cylinder, with no binding evident.

It's almost as though I have hydraulic lock in the cylinder, but I don't know what would be contributing to this.  Any suggestions?

Answer
Hello Bill:

From your Description, it Sounds like the Flywheel Key has Sheared. Remove the Cover that Houses the Starter Assembly. Use a Bolt the Same Diameter and Threads as the Spark Plug and About 3" Long. Thread the Bolt into the Spark Plug Hole Until it Engages the Piston. Slowly Tighten the Bolt Until you have Locked the Piston and it Does Not Move. **BE CAREFULL  A LOT OF TORQUE IS NOT REQUIRED PISTON DAMAGE CAN OCCUR ID TO MUCH TORQUE IS USED ON THE STOP BOLT** Now Remove the Flwheel Nut. Use a 3 Jaw Puller and Attach the Puller to the Flywheel. Look for a Puller with Flat Jaws. These Slide Under the Flywheel and Allow for Easier Removal. Tighten the Puller and then Hit the Puller with a Hammer. Tighten and Hit Again Until the Flywheel is Loose and Can be Removed from the Crankshaft. Note the Key that Aligns the Flywheel to the Crankshaft. This Key is Most Likely Sheared or Bent and Causing the Plug to Fire Slightly Out of Time and Causing a Compression Lock. There is Not Enough Compression to Kick Back But Enough to Cause the Engine to Seem to Have High Compression. If you Hit a Snag or this Does Not Correct the Problem,  I am Here if You Require More Assistance. Hope this Helps. Let me Know What Happens, Please. Have a Happy Holiday Season and May the All Mighty Bless You and Yours. Be Safe and Happy. Thanks.

Good Luck

Respectfully

John

PS: I am Allowed to Answer 10 Questions a Day. If you See I am Maxxed Out, then Try Submitting your Question at or Just After 8pm EST (US). My New Day Starts then. Thanks.

Respectfully

John