These engines are prone to blowing head gaskets. Your symptoms are consistent with blown head gasket BUT could be something else. That is the first thing I would suspect. You may be able to pinpoint it by removing the valve covers and seeing if there is detectable leakeage from the combustion chamber into the push rod gallery while cranking. This is where they typically leak. IF you start the engine with valve covers off, there will be oil mist come out and perhaps more than mist. I can send you a Service Manual for the engine IF you like, address below, put in proper format and remind me, engine model number and what you want. Walt Conner wconner at frontier dot com

As Bill says. I can send you detailed instructions on adjusting the valve and or a Service Manual IF you like. Address below, put in proper format and remind me, engine model number and what you want. Walt Conner wconner5 at frontier dot com

Do I warm up the engine to adjust the valves or do it cold? What is the setting for the valves? What should the plugs be gapped at? I have a B&S 25 H.P. engine in my lawn tractor. I think it's a 2002 Craftsman.Thanks. Jim

Well you don't have a "piston problem". Sounds to me like you may have more than one problem though. Proper valve setting is .003" - .005" for Intake and .005" - .007" both set with engine cold and piston set at 1/4" down past TDC. Would ask you to send your address and then send you detailed instructions but I am leaving for the weekend. Walt Conner