[DeTomaso] Valve Height accuracy

[jderyke at aol.com]

In a message dated 12/25/09 9:14:58 PM, doug at silicondesigns.com writes:

> What say ye for valve spring height accuracy?  The Comp Cams catalog 
> calls for a 1.900" spring height for the beehive springs I'm using.  I measured 
> the valve spring heights on a pair of heads that had been professionally 
> prepared just to double check them.  I get a range of 1.853" to 1.872".  A 
> 0.047" error on the worst one seems high to me.  How close is good enough.
> 
Doug, it's not exactly the spring height that's important, its the spring 
pressure on the valve as-installed. Your cam card will tell you what load the 
springs should produce with certain heights to prevent valve float, and 
your mechanic will add spring-shims under the springs to adjust the load (up to 
a point). Most brand new springs will install at one pressure then drop 
somewhat within a week, then hold that pressure for a long time. Perfectionists 
run the springs until the initial drop-off, then tear a few off and check 
their load vs the height & re-shim all of them as req'd. FWIW- J DeRyke