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Exhaust Valve to Piston Collsions

Engine

Model: 944, Year:1983, Mileage:120000, Type of use:Both Street & Track
I have a 1983 944 with approximately 120K miles. The car is used mostly for daily driving but occasionally for autocross and a few DEs. Lately it has been sitting for weeks at a time. Last month I started the car after three weeks sitting and went for a drive. At the first traffic light I noticed a lot of valve train noise. I drove it to the local independent shop for diagnosis. Upon removing the valve cover it was observed that the woodruf key on the end of the camshaft had failed. This allowing the timing gear to move +/- approximately one tooth. It is not clear why the key failed. The slot in the camshaft and timing gear were in bad shape from the rocking. We have pulled the head to inspect for damage. The exhaust valves were hitting the tops of the pistons. The intakes valves never collided. The exhaust valves still sit properly in the head. They have surface marks from the collisions with the pistons. We are having the head disassembled to check for bent valves, valve guide wear, and valve seat wear. The tops of the pistons are marked where the exhaust valves were hitting. There apprears to be about a 1mm indent beyond the formed exhaust valve area. I would rather not dissasemble the engine further to replace pistons, etc as the cost is already exceeding the value of the car. The cyclinder walls look very good and all other observable wear parts look good. What is the likelyhood that the pistons are ok. Is there a test or way to check for surface cracks in the pistons. Thanks for your help. Tom

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