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We've had difficulties with bore distortion on some 6.0L GM engines. Any clues?
The AERA Technical Committee offers the following information regarding a cylinder boring caution for 1999-2006 GM 6.0L VIN U engines. These engines are the newest version of the small block series and have been commonly called Gen III engines.
It has been reported that cylinder bore distortion is prevalent in these blocks. Therefore, it is extremely important to use a stress plate while boring/honing for oversize pistons. The pistons used for this engine are a short skirt design, and piston noise is likely if excessive clearance exists. In some instances, on engines bored/honed without a stress plate, the noise is only noticeable during initial start-up. In other cases, however, the noise decreases as the engine warms but it does not completely disappear.
As much as .002" out of round has been reported when measuring bore size with and without stress plates installed. Each block (and cylinder) may vary on the exact amount of distortion as cylinder wall thickness is not identical on all blocks.
To measure distortion on a particular block, it is suggested to measure and record bore sizes for all eight cylinders. Then, install a new head gasket and torque the bolts in sequence (Figure 1):
Tighten the 11 mm bolts (1-10) in sequence to 22 ft.lbs. (30 Nm).
Rotate bolts (1-10) in sequence an additional 90° turn using a torque angle meter.
Rotate only bolts 1-8 in sequence an additional 90° using a torque angle meter.
Rotate the remaining 11 mm bolts 9 and 10 in sequence an additional 50° using a torque angle meter.
Install the 8 mm bolt and tighten those bolts (11-15) in sequence to 22 ft.lbs. (30 Nm).
Then, flip the block over and take measurements from the bottom side of the block and compare to the first measurements made before the heads were installed. Make sure to also torque the main bolts as well before measuring.
We've had a few complaints of oil leaking around valve covers on some 3.2L GM engines in cold conditions. Any solutions?
The AERA Technical Committee offers the following information regarding an engine oil leak from the camshaft area of 2003-2004 GM 3.2L VIN N engines. This condition has been most noticeable during extremely cold weather conditions and is most prevalent on the left side just below the oil fill hole in the cam/valve cover.
This condition may be due to the closed crankcase ventilation system becoming blocked by ice. When the ventilation system is blocked, the crankcase vapors and engine oil will then vent through the cam/valve cover seals.
To repair this type of condition, GM now offers a revised Positive Crankcase Ventilation (PCV) hose kit and oil filler cap (see Figure 2)
. Installing the kit and cap will keep water from accumulating and freezing in the ventilation system. The PCV kit is available as p/n 55558592, and the oil filler cap is p/n 12589430.
The PCV Kit repair also involves;
Enlarging two drilled holes in the primary vent hose adapter.
Shortening two existing hoses.
Installing a new secondary PCV vent hose adapter
Resealing the entire system.