quote:
Originally posted by Robbie:
I suppose the "it lasted 132,000 miles with no problem" philosophy doesn't apply to valves.
Unfortunately no.
I wish I knew what factors were involved, if so it might be possible to predict what the chances are of the valves failing based on the history of your car's engine.
This is not a problem peculiar to the 351C. There are other vehicles (cars & motorcycles) which have had similar "brittle valve" issues over the decades. The stems of the "brittle valves" develop microscopic cracks, those cracks develop into larger cracks, and every once in a while a crack becomes so severe that the valve head separates from the stem. Some folks think the development of microscopic cracks is related to the constituents of the fuel you burn in the engine combined with environmental factors like humidity. Some believe extended periods of non-use are a contributing factor. But those are just conjectures, no solid studies have been done to my knowledge.
If you take a normal valve, clamp the stem in a vice, and grab the valve head with a pipe wrench you can bend the valve 90 degrees without breaking it. Do that to a 351C valve and you'll snap the valve head off. The 351C valves are brittle.