I have a Scotts 2554 with the 2 cylinder Kohler 25 HP engine. I was cutting some very heavy grass with it yesterday and it was chugging pretty good. Afterwards, the engine started a 'ticking' noise. The ticking happens whether or not the tractor is moving, and speeds up with RPM. It sounds like lifter noise. Could I have bent a 'push rod'? I'm religous on changing the oil and filter and have even been using Mobil 1 for the last 2 years. I have not had any problems with this tractor since new. Any thoughts on what this could be and what it will take to repair it? Thanks in advance.