PEP's
modern US Manufacturing facility can produce standard, special and
oversize bronze valve guides on very short lead time. The High Performance
Bronze Material also known as Bronzanium 90 is used in many high
end European and English cars. Our bronze material is also used
by high performance cylinder head manufactures worlwide.
In
most types of reciprocating engines, a bronze valve guide is provided for
each poppet valve in the cylinder head. Along with the valve spring,
it serves to positively locate the valve so that it may make proper
contact with the valve seat. A valve guide is a tube-shaped piece
of metal, pressed into the cylinder head, with the valve reciprocating
inside it. Guides serve also to conduct heat from the combustion
process out from the exhaust valve and into the cylinder head where
it may be taken up by the cooling system. Bronze is commonly used,
as is steel; a balance between stiffness and wear on the valve is
essential to achieve a useful service life.
In
aircraft piston engines, the valve guides are typically shaped in
a tube with a flare at one end, so as to resemble in section, the
letter "T". Their replacement involves removing the worn
part by driving it out with a hammer and specifically-shaped punch.
Installation involves heating the cylinder (with its integral head)
and freezing the valve guide so as to ease insertion, and then driving
the new guide in (quickly) with a hammer. Once the parts return
to room temperature the new valve guide will be solidly in place
and ready to be reamed and honed to proper diameter.
As
valve guides wear, their ability to positively locate the valve
to the valve seat decreases. As the valves lose their ability to
seal the combustion chamber properly, the engine can lose performance
and start to burn oil, leaking from the top of the cylinder head
into the intake and exhaust manifolds resulting in a need for a
valve job.