My mom got my grandma's tiller after her passing. It's a big older model Troy Bilt. Not sure on the model, but this thing is a beast! We serviced the motor and had it running no problem. When I tried to till with it it wasn't digging in. The tines would push it forward. It was just sliding the wheels since the tines were moving faster than them. The are forward rotating tines. Any ideas? Do you sharpen tines?