Usage:
3406, 3406B Truck Engines
Reference: Truck Engine News, September 1986, Page 1, "Indications Of Engine Overspeeding When Only One Cam Lobe/Lifter Has Failed " for 3406, 3406B, 3408, 3408B Truck Engines. Truck Engine News, November 1987, Page 4, "Results Of High Speed And/Or Overspeeding Of 3406B Truck Engines ".
Reference: Guideline For Reusable Parts And Salvage Operations; "Slipper Followers And Camshaft Roller followers "; Form SEBF8067.
Description of Change: A new lifter is used in all 3406B Truck Engines. The width of the center land is reduced on the new lifter. The reduced width improves oil flow through the lifter bores. This change will ensure that adequate oil pressure is maintained for compression brake system operation. This will result in improved performance and increased service life for the engine brake components. See Illustration 1 for oil flow for the 3406B Truck Engine. Restricted oil flow to the top of the engine can result in reduced compression brake performance and increased valve train wear.
Adaptable To: The new 9Y4011 Valve Lifter Assembly is a direct replacement for the former 4W7108 Valve Lifter Assembly (canceled). This change is effective with 3406B (4MG19071, 8T026780) Truck Engines. This change is adaptable to all earlier 3406 and 3406B Truck Engines.
NOTE: In truck applications using compression or exhaust operated engine brakes, a mid-life "lifter" inspection could be performed to identify any problems related to oil quality or severe application. Any rocker arm requiring a lot of adjustment could also indicate the development of a cam lifter problem.
NOTE: For correct engine operation, oil pressure must be maintained. The minimum oil pressure for the 3406B Truck Engine is 275 kPa (40 psi) when measured at Point (B) with engine speed above 1200 rpm. For correct operation of some compression brakes, a minimum oil pressure of 140 kPa (20 psi) is required at Point (C) with the engine speed above 1200 rpm. Under some conditions, the oil pressure at Point (C) may be lower than at Points (A, B or D). See Illustration 1. If there is a noticeable oil pressure drop between Points (B and C), the cam lifter oil passage may be restricted. In earlier engines, this can be fixed by machining a relief in the second land of the cam lifter. See Illustration 2.
Valve train damage on a single camshaft lifter, rocker arm, or bridge may occur from excessive valve lash. Always check the amount of valve lash during engine disassembly when investigating a single lifter failure. See Illustration 3 for areas to check for possible damage.
For a general view of all major components applicable to this change, see Illustration 4.
Illustration 1. Engine oil flow schematic. (1) Bracket for rocker arm shaft. (2) Rocker arm shaft. (3) Oil passage to lifters. (4) Valve lifter bore. (5) Oil supply rocker shaft bracket. (6) Rocker arm shaft. (7) Oil supply rocker shaft bracket. (8) Oil passage to accessory drive (air compressor). (9) Oil passage to rocker shaft bracket and accessory drive. (10) Oil passage to idler gear shaft. (11) Oil passage to rocker shaft bracket. (12) Oil passage to the fuel injection pump housing. (13) Camshaft bearing. (14) Oil jet tubes. (15) Main bearing. (16) Oil manifold. (17) Oil passage from the oil pump to the oil cooler and filter. (18) Oil passage from the oil cooler and filter.
Illustration 2. Machine to these dimensions to modify the lifter assembly.
Illustration 3. Location of damaged areas on lifter assembly (19), bridge (20), and rocker arm (21) from incorrect adjustment.
Illustration 4. The major components affected by this change are: lifter arm assembly (22), bridge (20), lifter assembly (19).