Cylinder Head Correction - Head Games z

15 Cylinder Head Tips And Tricks For Power And Reliability

Mike Petralia Jul 1, 2001 0 Comment(s)

Seal Clearance
After installing your new valve stem seals, it's important to check retainer-to-seal clearance. Using a dial caliper as shown will tell you exactly how much lift you can run until the retainer smashes the seal. It's wise to stay about 0.020 inch below that number to counter-act any possibility of valve float or bounce. Different types of seals will offer different clearances, so be sure to check. It's also a good idea to check this if you have already run the PC seals with no problems but are planning to increase rocker arm ratio for more lift.

Valve Stem Height
This step is important but often only done on high-end engines. Comparing and correcting valve stem installed heights is critical to performance. This valve stem height-checking tool from Silver Seal Products comes with numerous adapters to fit any type of head. If these heights are not equal, then each rocker arm will have to be measured, and different length pushrods will have to be cut for every valve. Stem heights can be altered by switching valves around, by machining the valve seat deeper, or by cutting a small amount of material from the valve stem tip. Be sure to consult with your machinist before you start cutting parts. Source: Silver Seal Products Company, P.O. Box 1050, Dept. SC, Trenton, MI 48183, (800) 521-2936.

Plug Chaser
New aluminum heads often come with the spark plug threads less than perfect. Powerhouse Products offers this spark plug thread chaser that will clean and fix any bad plug holes. While it's best to chase the threads with the heads off the engine, you can fix crossed threads with the heads on the motor by applying a liberal amount of grease to the chaser and running it in. The grease will hold any chips, and you can carefully wipe the grease out of the hole afterwards. The chaser is made to fix threads for both 14mm and 18mm (5/8 and 13/16 hex) plugs. There's even a rubber O-ring on the chaser to hold it in a socket if you're doing this in the car. Information: Powerhouse Products, 3402 Democrat Rd., Dept. SC, Memphis, TN 38118, (800) 872-7223,

Seal The Threads
This step is a headache saver. Factory Chevy blocks, excluding Bow-Tie racing blocks, all have head bolt holes that run right into the water jackets. And hot, pressurized water will definitely make its way up past the bolts if you don't properly seal the threads. While we haven't found the perfect sealer for every engine yet, GM's Teflon thread sealer seems to work well in most cases. Apply a liberal coating around the entire thread surface and let it "tack up" for a few minutes before installing the bolt. High-temp RTV silicone also seems to work, along with Permatex Form-a-Gasket, if you apply it to both the bolt and inside the hole and let it tack up before threading the bolt in. Of course, no sealer will work in dirty threads, so be sure to always clean and chase the head bolt holes with solvent and a thread-cleaning tap like those available from ARP. Sources: ARP (805) 278-RACE (7223), Nearest GM Performance Parts dealer (800) 577-6888.

Correct Length
Anytime you install new heads or even change your head gaskets to a different thickness, you should always verify correct pushrod length. The ideal pushrod length will cause the rocker arm's roller tip to sweep evenly across the valve stem tip with it centered at about mid lift. Too short a pushrod will put unnecessary stress on the valve stem tip as it tries to push it towards the outside of the head. And too long a pushrod could put the roller tip over the edge of the valve at max lift. Adjustable pushrod length checkers are available from all the major cam companies. Remember that big-blocks use two different length pushrods and small-blocks use a different length still, although exhaust and intake are the same length in most small-blocks.

Port The Studs
It's a necessary evil that rocker arm studs must protrude into some of the intake ports. Sometimes the protrusion is so minor that it won't hurt performance at all, but other times the stud can create a serious obstacle for the air to move around. It's wise to check each stud that protrudes into the ports before installing the heads. If the stud sticks in the port as much as shown here, then torque it in place and use a carbide cutter to contour it to match the port wall. This is an important step even if you're not porting the heads since not all ports have a rocker arm stud in them, and they will flow differently otherwise. Always remember to seal these threads to prevent oil from being sucked into the intake ports.




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