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Re: [T3] Further research and experimenting material!

<x-charset iso-8859-1>On Wednesday 07 November 2001 00:37, Hal Sullivan wrote:
> At 08:32 PM 11/6/01 -0600, Jim Adney wrote:
> >The way I see it, however, the biggest contribution comes from the
> >differental thermal expansion of the various parts and the fact that
> >the cylinders and head studs are steel while the pushrods are
> >aluminum (which expands 3x as much as steel.)
> Now *this* I want to check out.  I'm using chromoly pushrods in one of my
> aircooled VWs --  I'm going to have to start measuring my valve lash both
> cold and hot, keep a chart of what I find.
> I've heard theories that the reason for the valve clearance is due to the
> different expansion rate of the aluminum pushrods relative to the rest of
> the engine.  Following that theory, chromoly pushrods should expand at the
> same rate (or nearly so).  If that's the case, would the 004/.006 clearance
> be as necessary in engines that use chromoly pushrods?
Also remember that the heads are involved in this expansion. VW changed their 
clearance settings when they redesigned the heads, not when they changed the 
push rods. 
The original 40hp and early 1500cc heads had rocker studs that were about 
3.5-4 inches long. When they got rid of these, they reduced the valve 

Russ Wolfe
'71 Fastback AT
'66 Fastback MT (IT RUNS)

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