Installation Instructions

Big Block Chevy Aluminum Heads

AFR would like to congratulate you on your purchase of the highest flowing and strongest castings currently offered in a “production” style BB Chevrolet Cylinder Head. These heads, properly installed and maintained, will generate impressive power figures and provide you with years of trouble free service. The following instructions and guidelines are meant to assist you in the proper installation and set-up of your new cylinder heads. It is important that you read through all of this information before attempting installation!!

Inspection:

Check all machined surfaces for nicks, burrs, etc., that might have occurred during shipping or storage. If necessary, carefully dress with a file, or sandpaper supported flat by a straightedge. This is especially important on the head deck and intake manifold flange to have an effective trouble-free gasket seal.

Valve Springs:

It is the customer’s responsibility to check and make sure that spring pressures are correct for his/her camshaft application. We recommend a minimum of .060” clearance from coil bind at full valve lift.

Valve Guide Clearance:

Our typical valve guide clearances are .0013-.0016. In some severe applications with heavy nitrous, marine endurance racing, or blower usage, looser guides might be required. Check with your engine builder.

Piston Dome Clearance:

Piston dome to combustion chamber clearance MUST be checked prior to final engine assembly. This is especially important on pistons that have a .700" + dome heights which are common on high compression 427-511 based engine configurations. Pay special attention to the crest in the chamber directly across from the spark plug. Consider .040 minimum clearance with 7000 rpm or less. Slightly more would be required for motors that are turned higher.

Engine Bulder's Tip:With some domed aftermarket pistons, it may be necessary to slightly clearance or modify the piston due to our more modern (efficient) heart shaped combustion chamber design. Most of the newer manufacturer's dome profiles will clear. Note that usually less than 1cc of aluminum is removed which only equates to a weight reduction in the piston of one to two grams. If your rotating assembly is already balanced this is a non-event and creates a very slight overbalance which in theory brings your engine into a better balance at slightly higher RPMs. While some of you might be inclined to remove the material from the actual cylinder head, note that all of the combustion chamber shapes are very critical to flow and altering the cylinder head can and will effect flow and power production. The easiest way to check for this is turning the engine slowly over with the cylinder head installed without the head gasket.

Piston to Valve Clearance:

It is your responsibility to check and make sure you have adequate piston to valve clearance before final engine assembly. Don’t forget to check radial (side) clearance as well.

Spark Plug Clearance:

In the event your engine has extremely tall piston domes, it might be necessary to index the plug electrodes and/or slightly clearance your piston domes to provide a minimum of .060” from piston dome to electode tip. Do not use projected tip plugs with extremely tall dome design (unless you are certain you have enough clearance).

Note: While on the subject of clearance, it is vital that you check clearance of all moving parts due to the vast array of rocker arms, lifters, cams, springs, etc. Don’t forget to check pushrod to head clearance as well as any potential interference from your rocker arms and spring assemblies prior to final engine assembly.

Rocker Studs:

AFR BB Chevy heads require two different length rocker studs. The (8) shorter studs (referring to the coarse thread length that screws into the head) should be installed on the intake side with a small amount of Teflon or some other non-hardening thread sealer. Conventional bolt thread lubricant can be used on the longer (8) exhaust studs. Never use a shorter stud on the exhaust side.

Note: Torque Rocker Studs to 55-60 ft/lbs.

Valve Seats:

Both intake and exhaust valve seats are heat treated ductile iron and are compatible with unleaded fuels.

Guide Plates:

Only AFR guide plates will properly fit our AFR Big Block Chevy cylinder heads. We carry them in stock under AFR part #6109.

Pushrods:

All AFR cylinder heads will require pushrods that are longer than stock length. The most common lengths are a +.200” to a +.250”, however, due to a large number of variables (deck height, cam base circle, lifter height, etc.) all pushrod lengths must be physically checked to achieve proper valve train geometry. For detailed information on pushrod lenght, please view the FAQ section of our website.

Stud Girdle:

All of our BB Chevy Cylinder Heads have been designed with valve angles rolled over two degrees from stock location to provide better flow characteristics. Stud girdles produced for stock chevy castings as well as other aftermarket pieces that have standard valve angles will not fit properly. We stock a high quality girdle in a convenient two piece design that will fit our heads correctly. (Most girdles that fit Dart Heads will also fit due to their two degree roll-over design as well.)

Head Studs/Bolts:

AFR BB heads take one inch longer fasteners along the exhaust port (bottom) side of the cylinder head. AFR offers complete kits or partial kits (studs or bolts) for the eight additional longer fasteners.

Note: We recommend the use of studs due to the higher clamping load they place on the cylinder heads. Blown, turbo, or nitrous engines should always use studs due to the much higher cylinder pressures they create.

Recommended Gaskets:

Head Gaskets:Mark IV Block 4.540 Bore Felpro 1017-1

Note: 1017-2 is .051 compressed thickness

Mark IV Block 4.630 Bore Felpro 1057
Mark IV Block 4.625 Bore Felpro 1093

Note: O-ring perfectly round, .051 thick, typical “pro-stock” style gaskets.

Mark V-VI 4.540 Bore Felpro 1047 or 17048
Mark V-VI 4.630 Bore Felpro 17049

Note: All after market Merlin and Dart Big Blocks accept "Mark IV" style head gaskets.

Intake Gaskets: (For best fit) Felpro #1275
Mr Gasket #121

Note: Do Not port match your intake manifold to these manufacturer gaskets or Fel-Pro Gaskets, as they do not exactly fit AFR heads. Only use AFR’s gaskets for port matching. Most other gaskets have a slightly larger entrance. You will see NO PERFORMANCE GAIN by opening your heads or intake manifold to the larger gasket opening.

Exhaust Gasket: Felpro #1412

Spark Plug Recommendation:

(Flat seat with gasket, .750 long reach, with a 5/8 hex head)
Autolite #3932 std. tip. race application Champion #C59C Std. Tip. race application Champion #R12YC Projected tip, Street application

Note: Other spark plug manufactures offer plugs that will also cross-reference and fit our AFR BBC castings. Always consult with the manufacturer for heat range that best fits your application.

Head Bolt Torque:

All AFR BB Chevy Cylinder Heads should be torqued to 75 ft/lbs. This should be done in the proper General Motors sequence in 15lbs increments beginning at 30ft/lbs. Moly lube should be applied between fasteners, washers, and area around head bold to prevent galling and improper torque valves. Sealer should be applied to all thread areas of fasteners that enter into block water jackets. Sealer is unnecessary with blocks that have “blind holes” in the deck surface and do not go into water.

Valve Length:

Intake Valve 5.500” (+.250)
Exhaust Valve 5.450” (+.100)

Important:

Apply anti-seize to all bolts and sparkplug threads to insure long thread life.

Coolant:

It is important to maintain 50/50 mix of antifreeze in the cooling system to prevent corrosion of aluminum heads. Do not use tap water, use distilled water instead. Most supermarkets sell purified or distilled water. Check labeling to verify purified through deionization.

Head Fastener Re-Torque:

All high compression, supercharged, turbo and nitrous motors should receive a re-torque after the first running and complete cool-down. Be sure to back off the fastener about 1/8 of a turn to eliminate false readings from “break-away” torque. Always re-torque in the same general motors sequence you initially tightened them with.

Valve Lash:

Be aware that an aluminum headed/iron block combination usually requires approximately .006 tighter lash when it is cold. An all aluminum engine could be as much as .010-.020 tighter when the motor is cold. Every motor is different, but these guidelines should get you in the ballpark.

Valve Tips

Do not grind your valve tips. Some AFR cylinder heads have harden stellite tips which cannot be re-ground. If ground the tip will mushroom over causing severe damage. If your valve tips are magnetic you can grind a maximum of .015 from the tip.

Cleaning:

AFR thoroughly cleaned your cylinder heads prior to shipment. Your heads were washed in water soluble chemical agitation tank and blown out with high pressure air 3 to 4 times before they were boxed. However during some machining operations chips are packed and wedged into the water jacketing and occasionally come loose in transit. Keep in mind one chip the size of a dime breaks into hundreds of tiny chips and makes the situation appear much worse than it is in reality. It is not usually if you blow high pressure air into the water jacketing to see additional foreign debris, or chips finding their way out. AFR recommends that you thoroughly blow out your heads prior to installation.