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On Fri, 2005-11-11 at 20:59, Jim Adney wrote: > On 11 Nov 2005 at 15:18, Russ Wolfe wrote: > > > As for stretching valves, this has been proven by VW back in the '60's > > to be caused by worn exhaust guides. > > So, are you saying that exhaust valves DO sometimes stretch? If so, > how much might one stretch? > > 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. This is one reason I ALWAYS replace the exhaust valves, and the guides on any head I do, unless when I measure the guides they are found to be OK.. -- Russ Wolfe '71 FB AT '66 FB MT '64 T34 (not running) '65 T1 (not running) '05 KIA Sorento SUV russw@classicvw.org http://www.classicvw.org ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~