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I've noticed different length head bolts on some 8.1L GM engines. Are there different torque specifications also?
The AERA Technical Committee says the following information should be considered any time a cylinder head is installed on 2001-2005 GM 8.1L VIN E and G engines.
Three different length mounting bolts are used to secure the cylinder heads for these engines as shown in Figure 1. These bolts are intended for a single-use and must be replaced once removed.
Do not reuse the cylinder head bolts. New cylinder head bolts must be used. The cylinder head bolts are torque-to-yield bolts and cannot be reused once the initial torque is applied. During the initial torque of the cylinder head bolt, the cylinder head bolt is stretched to achieve proper clamp load, which will not be achieved if a used cylinder head bolt is torqued again. A stretched cylinder head bolt can also break when torqued. Failure to replace the used cylinder head bolts with NEW cylinder head bolts can lead to improper clamp loads and extensive engine damage.
Sealer is also required on the bolt threads prior to installation. Two different head gaskets are also required. The left side is available as p/n 12580691 and the right side is p/n 12580692.
The sealer must be applied to a minimum of eight threads starting at the bottom point of the cylinder head bolt. If a pre-applied sealer is not observed on the new cylinder heads bolts, apply sealant (GM U.S. p/n 12346004, Canada p/n 1095348O or equivalent) to the cylinder head bolts.
Install cylinder head bolt using the following bolt tightening sequence. The final angle tightening sequence of the cylinder head bolts varies depending on the length of the cylinder head bolt.
Failure to angle tighten the specific length bolt the proper number of degrees can lead to cylinder head bolt failure or improper clamping load of the cylinder head gasket. Cylinder head bolt or cylinder head gasket failure can lead to extensive engine damage.
The long bolts are used in locations 1, 2, 3, 6, 7, 8, 9, 10, 11, 14, 16 and 17. The medium length bolts are used in locations 15 and 18. The short bolts are used in locations 4, 5, 12 and 13.
Tighten the cylinder head bolts in the sequence shown in Figure 2.
Tighten the cylinder head bolts a first pass in sequence to 22 ft.lbs. (30 Nm).
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Tighten the cylinder head bolts a second pass in sequence to 22 ft.lbs. (30 Nm), then rotate an additional 120° using J 36660-A (electronic torque wrench).
Tighten, in sequence, bolts 1, 2, 3, 6, 7, 8, 9, 10, 11, 14, 16 and 17 an additional 60°.
Tighten bolts 15 and 18 an additional 45° and bolts 4, 5, 12 and 13 an additional 30° for a final pass using J 36660-A.