1989-1998 Cummins Premium Stock Plus Head w/ Fire Rings (PDM-12VSTKH-FR)

Heads are first jet washed in a high-pressure spray cabinet to remove oil and dirt, then glass beaded to remove carbon. Next, they are checked by magnafluxing, (cast iron only) or pressure testing. They are visually inspected for defects that would make them unusable. Valve guides and seats are removed as needed for porting.
 
Port development is accomplished using a superflow 600 flow bench with a computer recording all flow measurements.
Many things are considered when designing a cylinder head Port; airflow is only one of the things to think about. Another major concern is port wall thickness.
 
Anyone can get a head to produce high flow numbers, but doing so leaves the port wall too thin causing the casting to crack. High-performance Diesel heads are more prone to crack because of the thermal shock experienced by excessive intermittent or long-term exhaust temperatures.
 
New High Strength Alloy, Heat Treated iron based valve guides are installed. These guides are heat treated to Rockwell 22 “C” Scale, which produces the ultimate in wear resistance. This is far superior to the original guide material, including Bronze. The guide incorporates a spiral grove inside the guide to hold oil and aid the lubrication of the valve during engine operation. 
 
Guides are then honed (not reamed) to the exact size using a diamond honing mandrel. Diamond abrasives allow for consistency of size, surface finish, and bore geometry with no variation from guide to guide. The guide size is then verified using a valve guide bore gauge.
 
Next, the head is treated to a multi-angle valve job to help maximize the flow of air in and out of the head. This is accomplished using a Serdi 100 guide and seat machine. Serdi uses a solid carbide straight-shank pilot. When inserted into the valve guide, it simulates the real valve stem during the centering process. This guarantees the valve seat is finished for a perfect valve-to-seat match.
 
Using CBN or Diamond tooling the head is given a new surface. With Industrial Injections berco milling machine, they can control the surface finish to accommodate different head gasket types. For example, MLS head gaskets require a very smooth surface finish.
 
Finally the head is jet washed dried and assembled with new valve seals and new performance valve springs.