Gen III V8 Piston or Crankshaft Repairs - keywords crank cylinder engine knock L59 LM4 LM7 LQ4 LQ9 LR4 LS1 LS6 noise pin rod tick

This PI was revised to add information about floating pin and fixed piston compatibility. Please discard PIP3691C.

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

When making a mechanical piston or crankshaft repair. There are engine mechanical differences that may be encountered depending on the year of the vehicle. When repairing a Generation III 4.8 5.3 or 6.0 V8 engine it may have a pressed fit piston pin. If GMSPO does not have stock on the pressed fit piston pin, a repair can be made with a new full floating style piston.

Below is a description of V8 engines and piston repairs.

4.8 5.3 and 5.7 engines with RPO codes LR4, LM7, L59, LS1 and LM4.

Full floating piston pins went into 4.8, 5.3, and 5.7 engines with the start of production in the 2005 model year.

If a dealer is servicing a 4.8, 5.3, or 5.7 engine that has a pressed fit style piston pin, a full floating style piston and rod can be used as a repair. If more than two pressed pin pistons need to be replaced with full floating pistons, it can cause a engine imbalance concern. If more than two pressed fit pistons need to be replaced with full floating pistons, replace all 8 pistons and install a 2005 model year crankshaft. If the engine has less than 100,000 miles the old piston rings should be reused on the new pistons. Install the rings in their original positions, and in the original cylinder they were removed from. No cylinder honing should be done when the old rings are returned to their original positions. Old pistons rings are reused so oil consumption will not be induced during the repair.

6.0 RPO Code LQ4

Full floating piston pins went into 6.0 LQ4 engines with the start of production in the 2005 model year.

2002 and prior model year LQ4 engines had pressed fit piston pins, and a first design crankshaft. If a piston repair is being made on a 2002 or prior model year LQ4 engine, and full floating pistons are being installed, the crankshaft must be replaced. The full floating pistons will not work with a 2002 or earlier LQ4 crankshaft. Use a 2005 LQ9 crankshaft and replace all 8 pistons when completing this repair.

All 2003 and 2004 model year LQ4 engines had the updated crankshaft but had pressed fit piston pins. The pressed fit pistons are the same weight and mass as a full floating piston. Mixing pressed pin pistons with full floating pistons will not cause a engine imbalance. If the engine has less than 100,000 miles the old piston rings should be reused on the new pistons. Install the rings in their original positions, and in the original cylinder they were removed from. No cylinder honing should be done when the old rings are returned to their original positions. Old pistons rings are reused so oil consumption will not be induced during the repair.

6.0 RPO Code LQ9

All 6.0L LQ9 engines (from the start of production) came equipped with full floating piston pins. All piston repairs on LQ9 engines should be made with existing GMSPO replacement parts.

See the following notes for additional detail:

Note: Due to engine build dates, it is possible to have a late build 2004 engine with full floating piston pins. If the engine has full floating pistons, repair with current GMSPO floating pistons.

Note: SI procedures for the Engine Block Inspection / Piston, Connecting Rod, and Bearings Cleaning and Inspection, should be completed during repairs.

Note: Do not use a fixed pin piston with a full floating style piston rod. A fixed pin rod should only be used with a fixed pin piston, and a full floating piston should only be used with a full floating rod.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.