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Number: Date: Model: SB213042 02/15/06 E-TechTM, ASETTM

(Also applies to Mack Trucks Australia)

Repair of Cylinder Head Gasket Combustion Leakage

Cylinder head gasket fire ring leakage will result in combustion gasses pressurizing the cooling system and forcing coolant out of the coolant recovery tank. This service bulletin outlines the proper procedures for diagnosing and repairing a combustion leak at a fire ring.

Combustion leakage at a fire ring is the least likely cause of coolant loss from the recovery tank. Always check the most common causes first, such as coolant leakage from the water pump or other source, defective water pump seal, faulty or incorrect pressure cap, EGR cooler internal leakage (ASETTM AC engines). Also, check for known cooling system issues and upgrades that apply to the chassis. For additional information concerning coolant loss from the coolant recovery tank (pushing coolant), refer to service bulletin SB232024. Two indications of a cylinder head gasket/fire ring combustion leak are an engine miss or a combustion leakage noise which sometimes sounds like a metallic valve ticking noise. Suspected combustion leakage must be verified as follows: 1. Apply a soap and water solution to the area of the cylinder head-to-engine block joint between the cylinder heads of a cold engine. 2. Start and run the engine at an idle while observing for the formation of bubbles in the area where the soap and water solution was applied. The area between the cylinder heads is the most typical location where combustion leakage occurs. If a very significant amount of bubbles is noticed, cylinder head gasket/fire ring leakage is indicated. As an alternative to the above test, test kits to determine if the coolant is contaminated with combustion gasses are available from most automotive parts store.

These test kits, however, only indicate whether or not the coolant is contaminated with combustion gasses. They do not determine where the contamination has originated (i.e., from a leaking cylinder head gasket or fire ring, or from a leaking EGR cooler in cooled EGR engines such as ASETTM AC engines).

SB213042 -- Page 1 of 5


If it has been determined that cylinder head gasket/fire ring leakage is causing pressurization of the cooling system and coolant loss from the recovery bottle, proceed as follows:

Before proceeding with removing the cylinder heads, contact your local MACK dealer. MACK dealers will contact the Mack Trucks Reliability Engineering department for authorization and further recommendations. 1. In preparation for removal of the cylinder heads, remove all the injection nozzle assemblies to prevent the possibility of damaging the nozzle tips and tops of the cylinder liners. 2. Remove both cylinder heads, and then clean and closely inspect the cylinder head combustion deck surfaces. Pay particular attention to the fire ring groove area at the rear of cylinder No. 3 and the front of cylinder No. 4, and any other location where combustion leakage was indicated. Inspect for fretting and groove wall erosion as shown in figure 1. If either is present, the cylinder head must either be replaced or the combustion deck of the head must be resurfaced. The fire ring grooves must also be recut. Unless the combustion leakage is in the very early stages, it is likely that this type of damage has occurred.


Figure 1 -- Enlarged Cutaway Side View of Fire Ring Groove

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3. Use caution when removing the fire rings from the tops of the cylinder liners. Do not simply place a screwdriver against the edge of the fire ring and hit it with a hammer. Doing so can chip the top of the cylinder liner. Use a thin bladed screwdriver or similar tool and pry under the fire ring until it pops loose.

If there is any damage or erosion to the coining bead, the liner must be replaced. A chip out of the liner top lip (fire dam) does not necessitate sleeve replacement. (Refer to figure 2 for an illustration of the fire dam and the coining bead.)


Figure 2 -- Cylinder Liner Fire Dam and Coining Bead Cross-Section

4. Inspect the cylinder liner coining beads at any area of obvious combustion leakage, and at the rear of cylinder No. 3 and the front of cylinder No. 4. Closely inspect the coining beads for signs of rounding or erosion. Rounding and erosion of the coining bead are usually found only when there has been severe, long-term combustion leakage. If the upper corners of the coining bead have even the slightest rounding at any location around the liner, the liner must be replaced. 5. Inspect the cylinder block top deck, paying particular attention to the area in front of cylinder No. 4. If combustion leakage has resulted in erosion of the cylinder block, the condition is acceptable as long as the erosion is not within 1/2" (12.7 mm) of a water port. Normally, if there is any cylinder block erosion, it is found at the front of cylinder No. 4 (or the rear of cylinder No. 3), well away from any water port. This is acceptable. If the cylinder block appears to be acceptable, thoroughly clean the top deck and all cylinder head bolt holes. Any head bolt holes that are rusted, corroded or contaminated with soot, should be cleaned, and the threads chased with an M16 x 2-6H tap.

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6. Measure and record existing cylinder liner stand-up height. Measure at four locations (left, right, front and rear) on each liner. The original installation stand-up height of a new liner for the various engine models should be as follows: E-TechTM engines -- 0.023"­0.029" (0.584­0.737 mm) (refer to the E-TechTM Diesel Engine Service Manual, 5-106) E-TechTM CCRS engines (except 380/410, 427 and 460 models) -- 0.023"­ 0.029" (0.584­0.737 mm) (refer to the E-TechTM Diesel Engine Service Manual, 5-106) E-TechTM CCRS engines (380/410, 427 and 460 models) -- 0.024"­0.029" (0.610­0.737 mm) (refer to the E-TechTM Diesel Engine Service Manual, 5-106) ASETTM AC engines -- 0.024"­0.029" (0.610­0.737 mm) (refer to the ASETTM AC Diesel Engines Service Manual, 5-111) ASETTM AI/AMI engines -- 0.023"­0.029" (0.584­0.737 mm) (refer to the ASETTM AI/AMI Diesel Engines Service Manual, 5-110) Clamping force of the cylinder head and engine operation results in a normal 0.001" (0.0254 mm) settle-in of the liner. For this reason, do not reshim a liner unless stand-up height is less than the minimum specification as listed above for the particular engine model. If it is necessary to reshim, perform the measurement and shim calculations using a target of the mean specification (0.026"/0.027", [0.660/0.686 mm]).

E-TechTM and ASETTM engines use a mid-flange liner, where the flange is 4 inches from the top of the liner. With the mid-flange liners, it is perfectly acceptable to attempt to have liner stand-up heights within 0.002" (0.051 mm) of each other, but it is not required. The stand-up height of a cylinder liner above the cylinder block deck (under the same cylinder head) may vary as long as all liners are within the stand-up height specification range.

E-TechTM CCRS engine models E7-380/410, E7-427 and E7460, as well as ASETTM AC engines, use cylinder liner part No. 509GC475, with a stand-up height specification of 0.024"­ 0.029" (0.610­0.737 mm). Cylinder liner part No. 509GC463 can be used in place of cylinder liner part No. 509GC475 as long as the specified stand-up height is achieved, either with or without the use of cylinder sleeve shims.

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7. For any cylinder liner that must be replaced or removed to increase stand-up height, inspect the cylinder liner seat surfaces in the cylinder block for pitting caused by cavitation erosion. If any such damage is seen, all liners must be removed and the liner seats inspected. For cylinder liner seat repair, instructions for the use of cylinder liner shims and cylinder liner installation procedures, refer to service bulletin SB211007 or the applicable engine service manual. 8. Reassemble the remaining engine components. Install new cylinder head gaskets and fire rings, and then reinstall the cylinder heads. Before installing the head bolts, they should be thoroughly cleaned. Any corroded bolts should be replaced. Install the head bolts, strictly following the head bolt lubrication and torquing specifications given in the applicable engine service manual. 9. Perform an engine run-in. The acceptable methods for running-in an engine are either running the vehicle on the road or testing on a dynamometer until normal operating temperature is achieved. 10. After a proper engine run-in, retorque the cylinder head capscrews in sequence by breaking each capscrew loose, one at a time, and then retightening to 205 lb-ft (278 N·m).

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5 pages

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