An engine includes a crankshaft, a piston coupled to the crankshaft, and a head positioned over the piston and cylinder. The head includes a first aperture therethrough profiled for a spark plug. The engine also includes at least one camshaft positioned in the head and a cam retainer positioned over the camshaft to retain the camshaft in the head. The cam retainer includes a second aperture profiled to at least partially overlie the first aperture. The cam retainer is in a sealed relation with the head at the interface of the first and second apertures. The engine also includes a valve cover receivable over the head and cam retainer and including a third aperture therethrough, the third aperture being profiled to at least partially overlie the second aperture, and the valve cover being in a sealed relation with the cam retainer at the interface of the second and third apertures.