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Small Block Chevy Cylinder Heads
As you may already be aware, there are is a dizzying number of cylinder heads available for the
Chevrolet smallblock. For over 40 years Chevrolet has developed heads for all types of uses,
including stock, high-performance, smog emissions and over-the-counter all-out race heads. Each
was designed in its day to provide the type of service intended and reflected the technology and
thinking of the times. Aftermarket head makers also have contributed to the design changes over the
years. The sheer number of choices can be mind-numbing. Just keep in mind what your intentions
are. That will help narrow the selection for you. Cast-iron heads are still cheaper than aluminum
heads, but some aluminum heads are being offered at reasonable prices. If you are going to use
unleaded pump gasoline for a street-driven machine, then the heads you build or purchase are going
to need hard valve seats in order to survive. Most factory heads made before 1975 had soft seats
that will have to be upgraded to hardened seats for today’s unleaded pump gasoline. Remember that
different heads have different amounts of chamber volume. These volumes have a direct effect on the
static compression ratio of the engine. What the compression ratio will be, in part, depends on which
head casting you use.
Closed chamber cylinder head with press in studs. Head casting number on a 336X head
The rocker arm valley on the 3947041 head has
pressed in rocker studs. Head casting number
and casting date of “I 11 8” can be seen,
indicating this head was cast on September 11,
1968, and used in the 1969 model year. This
particular closed chamber head was fitted with
1.94"/1.5" valves.
The head casting number on this “336X”
head is located in the rocker arm valley.
Chevy has used various raised casting symbols on the ends of smallblock cylinder heads, which on
some heads are duplicated in the rocker arm valley. These symbols were used to indicate the type of
features found on those particular heads. The same symbol can be found on different heads with
different casting numbers. These symbols are helpful, but should not be solely relied upon to
determine what type of heads you have or what features they have. For instance, the camel hump
symbol (also called double hump) can be found on 461, 461X, 462 and 291 casting heads. The 492,
292 and 186 heads have a slightly different looking camel hump. These heads may have come with
1.94"/1.5" valves or they might have been made with 2.02"/1.6" valves. The chamber shapes found
on the 461 and 461X heads are not the same as those found on the 291, 462 or 186 heads. The
461X castings are popular for racers because they actually had slightly larger port volumes as cast
than the 461 and other production heads. Some of these heads had accessory mounting holes, but
heads made before ’69 do not. Just to make things interesting, another casting, the 041, was basically
the same as the 186 heads, but did not have the camel hump casting symbol. The 041 heads have a
completely different right angle symbol on their ends. The point is, you need to look at all of the
identifiers on the head in order to know what you have. Some later head castings have the last three
digits of the casting number stamped into a ledge on the ends of the head that are visible when the
heads are on a motor. You may need a mirror to read them, because the ledge faces down when the
head is on the block. End casting symbols give you some clues, but they don’t tell you the whole story.
336X head with the shift clock casting 520 cylinder head casting number
This “336X” head also has the shift clock and
the “D” and “N” for Day or Night shift and the
rare “M” in the date code representing the
month of December. On some casting dates
Chevy felt that the use of the letter “I” for the
month of September might be confused with a
numeral “1.” So sometimes they skipped the “I”
in the monthly alphabetical sequence and “J”
was used for the month of September and then
“M” was used for the month of December.
This “520” rocker valley shows the casting
number and the Canadian manufacturing
location.
327 double hump head
Early 462 double hump head
The double hump or camel hump casting symbol
on the end of this head indicates a performance
cast-iron head used in the sixties. The lack of
accessory bolt holes in this head narrows the
possibilities as to which casting this is. Looking at
the head casting number revealed that it was a
“461” casting with 1.94"/1.5" valves that was
found on a 327/300hp motor.
Shown is a “462” double camel hump casting
symbol. These early heads did not have
accessory bracket bolt holes.
Casting identifier on a 041 head
Open changer verses closed chamber cylinder heads
Head casting identifier on “041” head is a symbol
of a right angle triangle. However, this 1969 to ’
70 high-performance head has the same
characteristics as the 186 high-performance
head, which has the double hump symbol. Both
heads were available from the factory with 1.94"
/1.5" or 2.02"/1.6" valve diameters depending on
the application. They have soft seats.
The 76cc open combustion chamber found on
the “993” casting on the left is noticeably
different than the 64cc closed chamber 186
casting on the right. Both of these Gen. I heads
came with 1.94"/1.5" valves.
292 angle plug head
Here is a “292” angle plug
head showing the single
camel hump casting
identifier symbol and the
accessory holes.
Smallblock heads have been made since 1955 and some of these heads are still in circulation. Many
things could have been done to these used heads over the decades. They might have had hard
seats from the factory or had hard seat inserts installed at a machine shop or may still have the soft
seats they were originally made with. They may have been ported (correctly or incorrectly). They may
have small diameter valves and pressed-in rocker arm studs or bigger valves and screw in studs may
have been installed. The heads may be cracked (not uncommon even on newer heads). Someone
may have added accessory bracket bolt holes to heads that didn’t originally have them (this is usually
crudely and badly done). They may be in such bad shape that they are not rebuildable. Be careful.
Some of these old heads are fit for use as boat anchors or hold downs for tent stakes, but not for use
on any engine.
Umbrella, positive and o-ring valve stem seals Various oil stem seals have been used
on smallblock heads. The most
common seal used on Gen. I heads is
the small O-ring style shown on the
right. The umbrella seal in the middle
rear is found in many rebuild kits. The
positive seals shown on the left slip
over the valve guides and can also be
used with double and triple valve
springs since they will fit inside the
innermost spring coils.
From 1955 to the ’59 model year, smallblock cylinder heads had a different staggered valve cover
flange bolt pattern. The top two bolt holes were closer together than the lower bolt holes. Valve
covers were made with bolt holes to match. In 1959, the valve cover holes in the heads were changed
so that the holes were the same distance from one another across the top when compared to the
lower holes. The 1959 and later valve cover holes were changed to match.
Late model head with positive locking valve stem seal 400 head with steam holes
Note that the late-model heads are using a
factory installed PC-type valve stem seal,
instead of the old O-ring that was used for
decades on the smallblock.
If you use a 400 block with steam holes in the
deck, you need to use a 400 head gasket and
cylinder heads with matching steam holes
(arrows). If your heads don’t have the holes, you
can use a 400 head gasket as a template and
drill the six additional holes in each head yourself.
Head with holes drilled to mount accessory bracketry
Cylindder head boss for water temperature sender
The single rear exhaust manifold bolt hole is
seen in this six-hole “336X” head along with
the boss for the water temperature sender.
When using the Gen. I long water pump, and
its associated pulleys and accessory brackets,
you need to use cylinder heads that have the
necessary bolt holes in their ends (arrows).
Heads cast from 1955 through ’68 don’t have
them, and with the early heads, you need to
use the short water pump, pulleys and
accessory brackets.
In 1987, the way in which valve covers were attached to the heads was changed again. The covers
bolt to bosses in the center of the rocker arm valley and the gasket was changed to accommodate
machined valve cover rails on the heads. This was done to help eliminate once and for all the
notorious valve cover oil leaks of previous designs. You can get an adapter (PN-24502540) that will
allow the use of the 1959 to ’86 flange-mounted valve covers on the center-bolt ’87 and up heads.

During the 1968 model year, head castings were changed so that a boss could be mounted in the
side of the head to mount the water temperature sending unit. Prior to that the temperature sending
unit was mounted in the intake manifold and the heads did not have a boss for the temp sender.
Some 1968 heads have the boss in the head, but the boss is not drilled or threaded.

In 1969, Chevy changed the way that engine accessory brackets were mounted. Prior to 1969, there
are no holes in the ends of cylinder heads on which to bolt accessory brackets. From 1969 onward,
the heads have threaded bosses and holes to mount the new style brackets. If you need these holes
to use your brackets, make sure the heads you plan to use have them. If they don’t have accessory
holes, use the earlier style, short water pump and pulleys with the related early style brackets for use
with short style water pumps.

From 1970 through 1980, 400 smallblocks were installed in various vehicles. These engine blocks
were different in that the cylinder barrels were siamesed in order to enlarge the cylinder bores to
4.125".
Intake and exhaust valve spring differences. Take a close look at the spring package on these two
Gen. I heads. The stock production head on the left has
a slightly shorter exhaust spring that also uses a valve
rotator (arrow). The head on the right uses intake and
exhaust springs of the same length, but no valve rotator
on the exhaust spring. The rotators are intended to turn
the exhaust valves at low rpm and help keep the valve
edges and seats clean. Don’t mix this up. If you are
building a stock set of heads with the rotators, use the
shorter exhaust spring. If you intend to use a larger than
stock camshaft and increase the spring pressures, don’t
use the rotators. Instead, install springs of equal length.
Previous | Next


This has been a sample page from

Chevrolet Small Block Parts Interchange Manual Chevrolet Small Block
Parts Interchange Manual
by Ed Staffel
Beginning with the earliest small block and carrying through the
very latest "Gen III" models, CHEVROLET SMALL BLOCK PARTS
INTERCHANGE MANUAL provides complete factory parts
interchange information, allowing the hot rodder to custom-build
his own high performance version of the famous Chevy "Mouse"
motor from off-the-shelf parts. Includes factory numbers, casting
marks, production histories, suppliers, component performance
capabilities, etc.

Only 2 Left in Stock, Order Soon!


This is a great book and one that any
enthusiast will love!
View Sample Pages
1)
Engine Blocks
2) Crankshafts
3) Oil & Lubrication System
4) Timing Chains & Covers
5) Cylinder Heads
6) Intake Manifolds
7) Ignition Systems
8) Gaskets
9) Exhaust Manifolds
Condition: NEW
Softbound
8.5 x 11-inches
144 Pages
300 B/W Photos
Item: SA55P
Price: $22.95
Click here to buy now!


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