Chevrolet Corvette 1963 Repair & Tune-Up Manual page 114

Valve Guide and Seat Service
The small-block engines (305,327,350) do not
have separate valve guides and seats. The
small-block head is basically a one-piece cast-
ing; the valves move inside guide bores and
seal against seats which are machined into the
cylinder head.
All big-block (396,427,454) cylinder heads
use separately pressed-in valve guides.
Chevrolet does not sell replacement valve
guides nor do they publish a factory recom-
mended procedure for replacing the guides.
They (the guides) can be replaced, but this
can be performed only by a professional au-
tomotive machine shop. Valve seats of cast-
iron big-block heads are machined into the
cylinder head; they cannot be replaced. These
seats, as those of the small-block, can be ma-
chined during a valve job to provide opti-
mum sealing between the valve and the seat.
Aluminum big-block cylinder heads use
hardened steel valve seat inserts pressed into
the cylinder heads. As in the case with big-
block valve guides, Chevrolet does not sell
replacement valve seats nor have they pub-
lished a factory recommended procedure for
replacing the seats. Due to the extremely high
cost of replacement aluminum heads ($600.00
+ each at the time of this printing) be abso-
lutely sure that the machine shop you chose
has a noteworthy reputation for precision
work.
Whether you have a small or big-block en-
gine, valve guides are most accurately re-
paired using the bronze-wall rebuilding
method. In this operation, "threads" are cut
into the bore of the valve guide and bronze
wire is turned into the threads. The bronze
"wall" is then reamed to the proper diame-
ter. This method is well received for a num-
ber of reasons: a) relatively inexpensive b) of-
fers better valve lubrication (the wire retains
oil) c) less valve friction (d) preserves the
original valve guide-to-seat relationship.
Another method of repairing worn guides
is to have the guides "knurled". The knurling
process entails cutting into the bore of the
Cutaway view of knurled valve guide
ENGINE AND ENGINE REBUILDING
\J
FOR DIMENSIONS,
REFER TO
SPECIFICATIONS
FirtM Rotation Tip Pattern
Proper
Up
Pattern
topln Rotator
Rotator
andchflcb lotaUon
Functioning
CHECK FOR,
BENT STEM
Typical valve stem wear patterns
DIAMETER.
valve guide with a special tool. The cutting
action "raises" metal off of the guide bore
which actually narrows the I.D. of the bore,
1/32" MINIMUM
Critical valve dimensions
thereby reducing the clearance between the
valve guide bore and the valve stem. This
method
same advantages as the bronze wall method,
but will generally wear faster.
Either of the above services must be per-
formed by a professional machine shop which
has the specialized knowledge and tools nec-
essary to perform the service.
107
toptaCT Rotator and cluck
rotation
VALVE FACE ANGLE
THIS LINE
PARALLEL WITH
VALVE HEAD
offers the