[DeTomaso] Bronze or Steel Valve Guides

[j g]

I believe that most of what has been said below is true.
Steel does not work correctly for guides  cast iron with higher carbon and silicon is the primary guide material in american cast iron cylinder heads when they are a seperate piece . 
Bronze guides actually expand faster than cast iron so usually will never  come out if proper shrink fit , press fit with adhesive and then an internal reamer to size is accomplished . The next way a bronze guide can be installed is as a screw in part similar to a real long helicoil . The valve guide usually cast into the head at the time of manufacture on heads ,is tapped with a special tap the valve guide helicoil is screwed in then staked then finished reamed to the valve stem  size and clearance . This  gives one a bronze self lubricating guide surface and minimizes problems with press in guides. 
 
jg 
--- On Mon, 7/19/10, JDeRyke at aol.com <JDeRyke at aol.com> wrote:


From: JDeRyke at aol.com <JDeRyke at aol.com>
Subject: Re: [DeTomaso] Bronze or Steel Valve Guides
To: cengles at cox.net
Cc: detomaso at realbig.com
Date: Monday, July 19, 2010, 12:15 AM


In a message dated 7/18/10 4:03:32 PM, cengles at cox.net writes:

> I am interested in learning aboutSteel vs. Brass (Bronze?) valve guides, 
> too.
> 
Real brass guides wouldn't last through a single Model T warm-up cycle, I'm 
afraid; too soft. 'Bronze' guides are usually phosphor-bronze, 
aluminum-bronze or silicon-bronze alloys.   It can wreck your day (and a few blades!) 
just trying to hacksaw a small piece of these materials--- very, very tough, 
hard and self-lubricating. I use phosphor-bronze for rack bushings. Often 
used for guides in aluminum heads to help counteract heat expansion, and they 
transfer heat better and faster than iron in performance engines. Some race 
engines use 'bronze' valve seats for the same reasons, but they don't stand 
up too long to the constant pounding from the valves.
If the shop gets a guide's shrink-fit or press-fit wrong in a head, the 
guide comes loose while the engine's hot & running and that act of the great 
game is instantly over. As for 'steel' guides, they are usually a type of cast 
iron. This works exceptionally well (especially in cast iron heads) because 
like a cylinder bore, the graphite in cast iron acts like a lubricant for 
alloy steel valve stems, fighting stem seizures. FWIW- J DeRyke
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