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A revised connecting rod cap screw for 1991-’98 Volvo 2.4L Code 57 engines
Engine Builders: The AERA Technical Committee offers the following information regarding a revised connecting rod cap screw for 1991-’98 Volvo 2.4L Code 57 engines. This change occurred at the end of 1997 engine production and all 1998 engines (S70/V70/C70 gasoline engines) have the revised cap screw.
The new screw has a closer thread pitch. At the end of model year 1997 approximately 800 engines were manufactured with this new type of screw. If an engine from a model year 1997 car is being renovated, it is important to check the type of screw, whether the screw needs to be replaced, and older engine connecting rods have been installed in a 1997-’98 engine.
When replacing the screw, use the same type with the same pitch of thread. Figure 1 describes how to spot the difference between the old and the new type of screw, and the chart (below) tells within which engine serial numbers mixed screw types are to be found.
The engine serial and type numbers are stamped into the right hand side of the cylinder block.
The type designation and serial numbers are also contained on a decal on the timing cover.
Engine Builders: Some truck operators of 1989-2002 Mack 12.0L E7 and E-Tech engines have expressed concern that even though the engine coolant temperature is within the normal operating range, the engine oil temperature indicated on the gauge is too high. Typically, the gauge indicates an oil temperature of 250° F, which is right at the beginning of the red zone on the gauge.
At full-load operation, engine oil temperature can be approximately 250° F on a sustained basis, and can intermittently reach temperatures between 250° to 270° F. Sustained temperatures of 250° F and intermittent temperatures of up to 270° F are acceptable. However, if engine oil operating temperatures exceed 250° F more than 20 percent of the time, and the oil has a minimum of 300 hours of service, the oil must be changed.
At a minimum, engine oil temperature should be maintained above the boiling point of water (212° F). At temperatures below that, moisture will condense and contaminate the oil with a light brown foamy emulsion of oil and water. This foamy emulsion will be found in the cylinder head cover areas of a cold-running engine. Engine temperature is primarily dependent upon ambient air temperature and engine coolant temperature. During full-load operation at normal spring, summer and fall ambient temperatures, there is a difference of approximately 45° between engine coolant temperature and engine oil temperature. So, with an engine coolant temperature of 205° F, an engine oil temperature of approximately 250° would not be uncommon.
During normal engine operation, oxidation of the oil can form sludge, acids and carbon deposits around the ring and inside of the pistons. Oxidation will also deplete the oil’s additive package. This is one reason why oil must be changed at regular intervals.
Some extended maintenance oils have a very good oxidation inhibitor, which allow longer oil drain intervals. Those oils will resist oxidation when short-term oil temperatures are above 250° F but less than 270° F (Short-term is defined as less than 20 percent of the total operating time on the oil).
Engine Builders: The AERA Technical Committee offers the following information regarding cylinder head service specifications for 1998-2002 Cummins 8.3L ISC/QSC "24 valve" or "4 valves per cylinder" engines. The current Cummins service information bulletin is 3666245. Previously published bulletins may be misleading as some information was incorrect.
The current bulletin includes an incorrect value for valve recession. The correct specification for both intake and exhaust valves is between .033-.047˝ (.859-1.210 mm).
ISC/QSC Cylinder Head Specs
- Valve Recession – Both intake and exhaust valve recession must be maintained between .033-.047˝ (.859-1.210 mm).
- Valve Guide Bore Diameter - .3157-.3185˝ (8.019-8.071 mm).
- Valve Stem Diameter - .3126-.3142˝ (7.940-7.980 mm).
- Valve Seat Angle – Intake 30°, Exhaust 45°.
- Valve Head Margin - .031˝ (.790 mm) minimum.
- Valve Spring Free Length – 2.340˝ (59 mm). (Part #3944711)
- Valve Spring Inclination - .059˝ (1.500 mm) maximum.
- Valve Spring Test Pressure – 203-227 lbs @ 1.200˝ (30.600 mm).
NOTE: Failure to follow the above specifications may result in piston to valve contact, white smoke or engine misfire.
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