what are some symptoms of a sheared flywheel key

I ran into the same issue last winter. The biggest giveaway for a sheared flywheel key is a noticeable vibration that gets louder as you hit the rev limiter, plus a metallic scraping sound that isn’t present at idle. I also felt a slight lag in power delivery when shifting into third. I took the engine apart to confirm, and the key was indeed broken in two. The fix was to replace the key and re‑align the flywheel precisely – otherwise you’ll keep getting the wobble. If you’re not comfortable with that, a reputable shop can do it fairly quickly.

I’d be cautious before assuming it’s the key. A loose flywheel bolt can cause a similar wobble and noise, and it’s a lot cheaper to check first. Try tightening all the flywheel bolts to spec and see if the vibration subsides. Also, inspect the timing chain tensioner – a worn chain can make a whining noise that mimics a bad key. If those check out, then the key is the next suspect. Remember, a sheared key can cause the flywheel to shift under load, which is a safety hazard, so don’t ride it long if you suspect it.

When I had a sheared key, the engine would suddenly lose a few RPMs under load and the throttle response felt mushy. The noise was more of a high‑pitched whine rather than a grind. I used a stethoscope on the flywheel housing and could hear the metal‑on‑metal contact. The trade‑off is that replacing the key often means pulling the engine, which is time‑consuming, but it’s worth it for reliability. If you’re comfortable with a basic teardown, you can check the key slot for cracks before committing to a full rebuild.