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On 11 Nov 2005 at 22:21, Russ Wolfe wrote: > 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 sounds like a cause for breakage. I thought you said this caused stretching. > 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.. I do the same, and make sure to buy GOOD valves, especially exhaust valves. -- ******************************* Jim Adney, jadney@vwtype3.org Madison, Wisconsin, USA ******************************* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~