Valve guide

Valve guide

In most types of reciprocating engines, a 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.

Aircraft engines

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...

Oil seals

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. Modern engines are fitted with valve stem oil seals which can be replaced if oil leakage occurs [1].

References

  1. ^ http://www.nwideuk.com/oil-seals/valve-stern-seal.asp

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