Perkins 1104D NH1 Systems Operation Testing And Adjusting page 60

60 RENR7967
Testing and Adjusting Section
The original valve guides are bored into the cylinder
head. When new valve guides(1) are installed, new
valves and new valve seat inserts must be installed.
The cylinder head must be rebored in order to install
the new valve guide. Valve guides and valve seat
inserts are supplied as an unfinished part. The
unfinished valve guides and unfinished valve seat
inserts are installed in the cylinder head. Then, the
valve guides and valve inserts are cut and reamed in
one operation with special tooling.
Refer to Disassembly and Assembly, "Inlet and
Exhaust Valve Guides - Remove and install" for the
replacement of the valve guides.