Hugh, the bronze valve guides need to be reamed after installation, to a
slightly larger clearance than would be used with original-type cast iron
guides (which normally don't have to be reamed). In a nutshell, the guide
holes in the head are not precisely machined, some are smaller than others,
and the bronze guides 'crush' a bit as they are pressed in, making the hole
smaller. The larger clearance is because bronze does not 'self-lubricate'
as well as cast iron, the extra clearance is needed to keep the valves from
sticking.
According to Ken G. at BFE, the clearance between the stem and guide should
be .002" intake, .003" exhaust. The machine shop that installs the guides
should know what to do with these numbers <g>
Randall
> One final question: I recall reading that the bronze inserts need some
> special treatment or else the valves may stick. Any advice on this?
>
> Thanks again,
> Hugh
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