This demonstration guide answers one field question about a bent crank stub or sheared flywheel key. Measurements come before parts, and the notes are not a generic equipment FAQ.
Diagnose before replacing parts
Start with crank runout at the blade adapter. That reading separates a bent crank stub or sheared flywheel key from adjacent faults that share the same complaint.
If the measurement is out of spec, treat the blade adapter and flywheel key as the primary path. If it is in spec, do not replace the blade adapter and flywheel key just to complete a parts list.
Repair the failed system
The usual correction is the blade adapter and flywheel key, installed to the documented spec for this complaint.
A demonstration shop records the finding so the next technician is not repeating a guess about a bent crank stub or sheared flywheel key.
Stop before you make it worse
Do not straightening a crank stub with a hammer. That shortcut hides the original measurement and creates a second failure.
If the machine still fails after the blade adapter and flywheel key is corrected, convert the visit to a broader diagnosis rather than stacking parts.
Written and published by Ridgeline Small Engine.