[T3] Those Muffler nuts~!

[Jim Adney]

On 9 Oct 2018 at 20:11, Keith Park wrote:

> all the built engines use them, that I know of.
> They were in the Raby 2056 kit, and yea, I think I have stiffer springs on
> it.
> 
> What kind of trouble?

The stock pushrods are alum with steel ends. Alum has a larger (3x) 
coefficient of thermal expansion than steel, which allows the pushrods to 
lengthen almost equally to the cylinders (since the cylinders warm up faster 
and run hotter) so the valve lash won't vary as much in the course of temp 
variations and warmup. It's a very clever system that's seldom appreciated.  

The stock alum pushrods are not as stiff as steel ones, so they work well 
with stock springs and within the stock RPM range, but once you get outside 
that range, steel pushrods may be needed to keep pushrod flex down. In that 
case, you give up thermal compensation for reduced pushrod flex.

So it's important to understand that steel pushrods are not an upgrade, they 
are a compromise to be avoided unless absolutely necessary.

When taking apart stock engines, we often find brite wear rings on certain 
parts of the pushrods. Those indicate that the engine has been run at higher 
than normal RPMs. The wear is usually not enough to damage the pushrod, 
as it's generally little more than enough to remove the oil deposits that are 
always there, but they are a nice tell-tale. If you find it on just one pushrod, it 
usually means that the pushrod tube is deformed and too close to the 
pushrod at that point. But if those brite rings are there, they are usually on all 
8 pushrods and indicate high RPM running.

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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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