The fit and finish of a valve determines the compression
and ease of movement of the valve. By rebuilding a piston valve, it is possible
to decrease any leaking as well as improve the "Action" or movement
of the valve in the casing. This page is meant to show the basic steps involved
in proper valve rebuilding. It is by no means a complete instructional guide
but should give the reader a good idea of the procedure involved.
Inspection of the Valve Casing and Valve
It is important to closely check the valves and casings
to assess the amount of corrosion and wear. The depth of corrosion has to
taken into consideration when honing. Excessive corrosion will increase
any measurements you will take when deciding on the amount of material to
Measurement of the Valve and Valve Casing
The valve diameter must be measured to determine if it
is cylindrical. All measurement is done with a micrometer and ID gages.
It is also helpful to see if
Scraping Valve Ports
The valve ports inside the valve casing will produce slight
burrs during honing. It is important to remove a small portion of the lip
around the edge of the inner valve ports. Great care must be taken while
executing this procedure. If the technician slips past the port hole and
scrapes the inside of the valve casing, irreparable damage can be done.
Actual scraping of the valve involves inserting the tool
into the casing, finding the port by visual inspection, applying the proper
amount of pressure while rotating the tool in the port hole.
Burnishing Valve Guide Slots
Often overlooked in the rebuilding of valves is the importance
of the valve guide slots to the proper operation of the valve. It is important
to remove any burrs or foreign debris from the slot and slot edges. The
valve guide must be allowed to move freely in the slot.
Although difficult to determine by eye, check the alignment
of the valve guide slot to the valve liners (ports in valve). Most spring
cages (upper half of valve which holds the spring) are soft soldered into
a grommet at the top of the valve. It is fairly easy to reposition the spring
cage by applying heat and flux to the valve placed in a lathe between centers.
Honing the Valve and Casing
The honing of the valve and valve casing is done on a machine
Likewise, the valve casing can be internally honed to
Preparation after Plating
After the valves have been plated they must be re-honed
to their new diameters. In the process of plating the ends of the valve
often are larger than the center section.
Lapping and Fitting
The final procedure involves lapping the valve into the
casing. Fine compounds
This page is not intended to be a tutorial but does demonstrate
many of the process involved in refitting badly worn or new replacement
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