I have a sears lawn tractor with the above described engine
Model 445677, type 0476Ei family 6Bsxs 7242vf 276480
It developed a loss of power, found it wasn't firing on one clylinder, removed valve cover. Both push tubes bent and displaced. No indication of valve piston contact nor bent valves. Checked other cylinder and it was OK.
I have no idea what caused this since I am unfamiliar with the internals of this engine. Do you have any ideas? schematics.\
I pulled the engine
That's the Intek OHV V-Twin, right?
********* Correction********
If it's the Intek V-Twin OHV the problem is the valve guides, not the seats. I have to remember not to post so early in the morning (before 10:00am). Usually the same source for the problem: overheating caused by lack of air flow over the cylinder. the real fix is to replace the cylinder head and gasket, but people have tried to repair the guides. A new cylinder head should be about $150 including the gasket.
If so, damaged valve seats are a fairly common problem, and usually caused by engine overheating due to air blockage around the cylinders. Sometimes a simple replacement of the valves is enough, but if there's damage to the cylinder it will cost $$$ for a new one. Some people have had luck repairing the valve seats.
Here's what B&S gas to say about it:
This failure usually occurs due to an overheating issue. Overheating is a cause of engine failure from an engine component material that has distorted beyond a specific yield point. The yield point is the limit of a material at which it can be exposed to heat or mechanical stress and still return to its original size and chemical composition. Overheating occurs from causes such as a lean air-fuel mixture, use of improper fuels, dirt and/or debris buildup on cooling fins, damaged cooling system components, reduction in cooling air, over speeding, or an improper engine enclosure.
Valve seat inserts are installed in the cylinder block using a press fit. A press fit is a method of attaching two mating components where one component is pressed into a machined hole having a slightly smaller diameter than the component inserted. Valve seat inserts are commonly .003 - .005 larger than the machined hole in the cylinder block. The pressed fit retains the valve seat insert in position with a constant force. This force is necessary as small engine have significant responses to heat generated in the combustion process. If the cylinder block expands past the yield point, the force is not present to keep the valve seat in place.
In some cases the valve seat can be peened back into place. However, there is no guarantee this type of repair will add significantly to the engine's life.
