GM 6.5L V8 – Cylinder Head Assemblies

The cylinder case provides mounting surfaces for two cylinder heads that are identical except for external hardware. Each one-piece cylinder head is made from cast iron and has the following features (refer to Figure 2-18):

• One pre-combustion chamber per cylinder, partially formed with a specially made cup insert
• Mounting surfaces for one injection nozzle and glow plug to project into each pre-combustion chamber
• Intake and exhaust ports with poppet-type valve assemblies
• A 17-bolt cylinder case mounting, providing 5-bolt clamping around each cylinder bore
• Cylinder bore and passage sealing with a special one-piece gasket (graphite coated)
• Cooling system passages
• Lubrication system oil drain-back passages
• Mounting surfaces for accessories and engine lift brackets

Each cylinder has a pre-combustion chamber to mix fuel and air efficiently, resulting in low exhaust emissions. An insert made of stainless steel forms one half of the pre-combustion chamber, while the casting of the cylinder head forms the other half. The shape and size of the inside of the insert is specific to the 6.5L V8 turbo diesel engine and should not be confused with inserts for other diesel engines.

Each pre-combustion chamber insert has a notch that aligns with a matching groove in the cylinder head (see Figure 2-19, view A). Insert identification markings for the 6.5L V8 turbo diesel application include two dots and the letter T.

During service, each pre-combustion chamber insert may be removed with a brass punch and hammer after the nozzle and glow plug are removed. Inspection of the insert includes a check for excessive heat cracks in the area of the flame slot exit (see Figure 2-19, view B). After installation, the insert must have a specified height (relative to the cylinder head surface) of 0 to 0.051 mm (0 to 0.002 in.).

During service, the procedure for installing a cylinder head gasket has the following critical steps:

1. Clean all cylinder head bolts and bolt holes to remove old sealant.
2. Check the cylinder case and head surface for excessive warpage:
– Limit of 0.15mm (0.006-in.) warpage across the length
– Limit of 0.075mm (0.003-in.) warpage across the width
– No damage in sealing ring or coolant passage areas
3. Check that each pre-combustion chamber is flush with the cylinder head surface (limit is 0.05 mm [0.002 in.] above surface).
4. Check that the alignment dowels allow the cylinder head to rest on the cylinder case.
5. Clean the cylinder case and head sealing surfaces.
6. Install a new head gasket.
7. Install the cylinder head assembly without scuffing the gasket.
8. Coat each cylinder head bolt with pipe thread sealant with TEFLON® on the threads and under the head.
9. Follow this tightening sequence (refer to Figure 2-20):
– Hand tighten all bolts.
– Tighten bolts in the specified sequence to 25 N-m (20 Ib-ft).
– Tighten bolts in the specified sequence to 65 N-m (50 Ib-ft).
– Tighten bolts in the specified sequence an additional 90 degrees of rotation.

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