And that's exactly how the other two have come off Mowerfreak. This one, I had the right size T20, ensured it was fully in, gave it a bit of a twist, and then a little bit more (just with a handle, not a 2m breaker bar or anything silly), and it just ate out the screw head like that. I don't know what the previous installer did (the clutch looks less than 5 years old), but they have really stuffed me up.
The Ryans are a really torquey motor and have tonnes of pull down lower in the rev range, but sometimes seem a little low on top end power for a 31cc. Still a great motor though.
