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Re: In Davenport


On 4 Aug 2006 at 10:36, topnotch@nycap.rr.com wrote:

> I think your 71 is probably a good candidate for a complete valve job.
> The rest of the car is in such good shape that it would be nice to
> have everything right on the engine with OE VW heads all freshened up,
> then you wouldnt have to worry about driving it anywhere (even if the
> 08 invasion is only a few miles away). That exaust valve showed guide
> wear on it, how much does it rock around in the guide?  I didnt think
> to check that when I was looking at it. 

The exhaust guide certainly showed some excess clearance, and I 
haven't taken the other valves apart yet, so I don't know if they are 
any different. At any rate, the wear on that particular guide is 
still quite a bit less than I've seen on other heads that I've pulled 
and rebuilt.

I'll plan on doing both sides sometime in the future, but probably 
not this season.

I've also been wondering how a valve could tighten up tighter than 
zero clearance. It seems like once it gets to zero the valve would 
have a tough time wearing into the seat any farther. According to 
Berg, as the engine warms up, the valve clearances go to zero and 
then approximately back to the cold settings. I'm guessing that this 
has to do with the cylinders expanding first, and then the pushrods, 
as they warm up later.

Wearing to negative clearance could only happen if the running 
clearance went negative at some point, and stayed there for a 
significant time. Side play in the guide could allow for some small 
amount of extra wear to the point of negative clearance, however.

Wear at the cam/lifter surfaces could explain a bit of this, but I've 
never seen significant wear on the "flat" part of a cam, and the 
removed head seemed to show enough wear at the valve seat to explain 
everything.  

-- 
*******************************
Jim Adney, jadney@vwtype3.org
Madison, Wisconsin, USA
*******************************

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