Think your job involves a lot of stress?
It likely pales in comparison to the job of a cylinder head fastener. With peak combustion pressures in excess of 1,500 psi in a high performance engine, the stretching and loading forces on your head bolts are incredible. That’s why you must make sure your head fasteners are in excellent condition and install them properly.
Adhering to recommended torque specifications and torque sequences is key to achieving a good, strong seal. Torque specifications vary depending on the fastener brand, lubricants, and other factors. Head bolt torque sequence, however, generally remains constant for a given engine. To give you a quick reference of torque sequences, OnAllCylinders’ Lori Sams has created a series of infographics for different engine makes. Today, we’ll look at cylinder head torque sequences for General Motors L8 and V8 engines.
First, here are few things to keep in mind:
Head Fastener Installation Tips
- Dirty or damaged threads can reduce clamping force, so inspect and clean your existing head bolts if you’re re-using them.
- Use new fasteners on a high-mileage or high performance engine, since there’s a decent chance it’s already been torn down and rebuilt.
- Make sure your existing bolt aren’t torque-to-yield (TTY) — this type of fastener is designed to stretch and cannot be reused.
- Check bolts in a set against one another to ensure none are stretched or deformed — damaged fasteners must be thrown out or replaced.
- When using stock fasteners, check your service manual for proper torque specs. Check with the manufacturer when using aftermarket fasteners as the specifications will vary. These torque values are usually based on oiled fasteners.
- Lubricate the threads and underside of the bolt head with motor oil or aftermarket lubricant. The slicker the lubricant, the greater the preload scatter (or error) during installation, according to ARP.
- Some manufacturers, such as ARP, recommend cycling the bolts to improving loading accuracy. This involves torquing the fasteners to about 50 percent of their recommended spec several times before reaching the final number.
- If you’ve had your cylinder heads resurfaced, you’ve altered their overall height. You’ll need to check that your cylinder head fasteners don’t bottom out in blind holes.
- Use hardened steel washers when installing aluminum cylinder heads. This will prevent galling of the soft aluminum.
- Check the accuracy of your torque wrench and recalibrate, if necessary, before bolting down your cylinder heads.
And finally, follow these torque sequences for your engine:
GRAPHIC BY: Lori Sams