1. Make sure all the head bolts are in perfect condition with clean, undamaged threads. Dirty or damaged threads can give false torque readings as well as decrease a bolt's clamping force by as much as 50%! Wire brush all bolt threads, carefully inspect each one, and replace any that are nicked, deformed or worn.
2. Dirty or deformed hole threads in the engine block can reduce clamping force the same as dirty or damaged threads on the bolts. Run a bottoming tap down each bolt hole in the block. The tops of the holes should also be chamfered so the uppermost threads won't pull above the deck surface when the bolts are tightened. Finally, clean all holes to remove any debris.
3. For head bolts that screw into blind holes, lightly lubricate the bolt threads as well as the underside of the bolt heads with engine oil. For head bolts that extend into a coolant jacket, coat the threads with a flexible sealer such as Fel-Pro Gray Bolt Prep (GRA2). Failure to coat the threads may allow coolant to leak past the bolt.
4. Many engines today use "torque-to-yield" (TTY) head bolts. These are specially designed bolts that stretch slightly when installed. This provides more even head loading and allows the bolts to hold torque better for improved head gasket sealing.
When the bolts are installed, they're first tightened to a specific torque -- then tightened an additional amount that's measured in degrees of rotation. This final twist stretches the bolts to their yield point and creates the elastic clamping force that provides more even loading across the head and gasket. Because TTY head bolts stretch slightly (only a few thousandths of an inch), some auto makers say they should not be reused when the cylinder head is removed. Reusing TTY bolts will cause them to stretch further, which increases the risk of breakage.
A stretched bolt also will not hold the same torque load as before, which may cause a loss of clamping force resulting in head gasket leakage. Ford says TTY head bolts on the 1.6L Escort engine should not be reused. Though not required, it may be wise to replace TTY head bolts on other engines if the vehicle manufacturer doesn't say to do so. Replacement TTY head bolts are available from Fel-Pro, and are recommended for Chrysler 2.2L and 2.5L, Ford 1.6l and 1.9L, and GM 1.8L, 2.0L and 2.5L fours, 3.0L V6 and 381 V8 diesel engines.
5. Check bolt lengths. Make sure you have the correct length bolts for the application and for each hole location (some holes require longer or shorter bolts than others). Bolts should also be measured or compared to one another to check for stretch. Any bolt found to be stretched must be replaced because (1) it may be dangerously weak, (2) it won't hold torque properly, and (3) it may bottom out when installed in a blind hole.
6. When installing head bolts in aluminum cylinder heads, hardened steel washers must be used under the bolt heads to prevent galling of the soft aluminum and to help distribute the load. Make sure the washers are positioned with their rounded or chamfered side up, and that there is no debris or burrs under the washers.
7. Resurfacing a cylinder head decreases its overall height, so be sure to check bolt lengths to make sure they won't bottom out in blind holes. If a bolt bottoms out, it will apply little or no clamping force on the head which may allow the gasket to leak. If a head has been milled and one or more head bolts may be dangerously close to bottoming out, the problem can be corrected by either using hardened steel washers under the bolts to raise them up, or by using a Fel-Pro copper head gasket shim in conjunction with the new head gasket to restore proper head height.
8. Always look up the specified tightening sequence and recommended head bolt torque values for an engine before installing the head gasket. Never guess. Complete cylinder head torque specifications for domestic and import vehicles are published in Fel-Pro's "Torque Tables" (486-93).
9. Use an accurate torque wrench to tighten standard type head bolts in 3 to 5 incremental steps following the recommended sequence and torque specs for the application. Tightening the bolts down gradually creates an even clamping force on the gasket and reduces head distortion. It's a good idea to doublecheck the final torque readings on each head bolt to make sure none have been missed and that the bolts are retaining torque normally. If a bolt is not coming up to normal torque or is not holding a reading, it means trouble. Either the bolt is stretching or the threads are pulling out of the block. With TTY head bolts, a "Torque-To-Angle Indicator" such as Fel-Pro's TRQ-1 should be used in conjunction with a torque wrench to achieve proper bolt loading. After the head bolts have been torqued to the specified value, using the TRQ-1 tool to accurately measure the additional degrees of additional rotation eliminates guesswork and assures more consistent results.
10. PermaTorque head gaskets do not require retorquing, but some head gaskets for import applications do. If a gasket requires retorquing, run the engine until it reaches normal operating temperature (usually 10 to 15 minutes), then shut it off. Retighten each head bolt in the same sequence as before while the engine is still warm. If the engine has an aluminum cylinder head or block, however, don't retorque the head bolts until the engine has cooled back down to room temperature.
On some applications with retorque style head gaskets, it may be necessary to retorque the head a third time after a specified time or mileage interval due to the design of the engine. Follow the vehicle manufacturer's recommendations.
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