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> From: Russ Wolfe > > > How does the worn guide cause this? > > > It is caused by the valve not hitting the seat square when it closes. > And each time, the valve is bent a little micron or so. and then bent > back maybe the next time. At the number of times the valve closes per > minute when our engines are running at highway speeds, the > metal starts > to fatigue. As it fatigues, and the seat starts to get hammered. The > valve settles into the seat, and due to the metal fatigue, the valve > eventually breaks if not replaced. Ah, that makes a lot of sense. I lost exhaust #3 on a beetle at 65mph once. Very messy. High mileage engine that probably hadn't been well looked after. Someone once told me the valve head was welded to the stem, and that's where they broke, because it was a weak point. Fits the symptoms but thinking about it they would never make them that way! Would the exhaust tend to go first due to hot gas further eroding the brittle fatiguing zone ? -- Matt. UK. '73 1600e FB. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~