On 5/12/2012 8:39 AM, Joe Alexander wrote:
> I think we all agree that bronze valve guides are good to use, if:
>
> they are properly clearanced...per Greg Solow, for instance.
>
> and if they have good material chemistry and properties.
>
> OK....CHUCK GEE or other metalurgist, what would you recommend for metal
> specification?
>
>
As a general rule, most all of the guides will be some alloy containing
aluminum and phosphorus. The higher the aluminum content, the more
likely they are to grow, so one could probably do a comparison by
weight, assuming the dimensions were the same from different suppliers.
There's one more trick that can be done to bronze guides that isn't
useful with the cast-iron variety--knurling. Aluminum bronze guides are
more malleable than cast iron. Trying to knurl the cast iron simply
causes it to chip, while the bronze guide will deform, making a ridge in
the guide bore. Once that ridge has been reamed to the correct size,
there are two advantages over using a stock bore. First, the guide
tends to retain oil longer, rather than pumping it straight down the
guide bore, and second, the contact area of the guide bore is reduced,
making the valve less likely to stick. And, even with the reduced area,
the wear characteristics are generally better than cast iron, and a good
bronze guide can be knurled a couple of times before requiring replacement.
Worth some experimentation, maybe. The business about valves sticking, I
think, has much to do with improper clearances, and not the material
itself, since the natural lubricity of phosphor bronzes is pretty good
compared to cast iron, something demonstrated by the ability to use
valve stem seals with bronze guides. Once the clearances are set up
properly, and good stem seals found, bronze guides should contribute to
a more consistently performing engine simply because the ability to use
stem seals will reduce the amount of carbon accumulation on the valve
heads and stems, keeping flow closer to optimum.
Cheers.
--
Michael Porter
Roswell, NM
Never let anyone drive you crazy when you know it's within walking distance....
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