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Detroit Diesel Series 149 Parts Detroit Diesel Series 149 Parts

Parts for Detroit Diesel 12V149

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An important first step is to locate the serial number, which will be near the model number. To differentiate, the model number will start with a 9 and be eight digits long. The serial number will be the other number. The serial number can also help you identify if you engine has a left-hand rotation or a right. An engine with a left-hand rotation the fifth digit will be three. If the fifth digit is seven, then it is a right-hand rotation engine. Look for the serial number on the right front cover of the block, on the rocker cover rail on, viewed from the flywheel. This is an important step when buying certain Detroit Diesel 12V149 parts.

How to Disassemble a 12V149 Engine

Attach a chain hoist to the brackets. Lift the cylinder blocks into a vertical positions and rest the end of the rear cylinder block on a clean flat surface. Remove the fifteen bolts securing the cylinder blocks together. Remove four 5/16 in. – 18 x .63 in. bolts and lock washers from the two center upper cylinder block drain screens, which are located in the cylinder head area between both blocks. Remove both drain screens. Lift the front cylinder block off the rear cylinder block and remove the seal strip and seal rings from the rear block.

Detroit Diesel 12V149 Crankshaft

The series 149 crankshaft is steel forged and heat treated to be strong. The 12V149 and 16V149 crankshafts are bolted together. After 1988, unidirectional crankshafts incorporate a change to the bolt holes used to attach either the flywheel or vibration damper hub. Former crankshafts used 5/8 in -18 bolts on a 127 mm (5 in) diameter bolt circle for attaching flywheels and front crankshaft damper hubs. Current crankshafts use ¾ in – 16 bolts on a 4.75 inch diameter bolt circle. As a result, former flywheels, generator couplings and vibration damper hubs cannot be used with the current crankshafts. Rotation is determined from the front of the engine. An arrow on the rear crankshaft butt also indicates the direction of rotation.

Installing Crankshaft Thrust Washers Detroit 12V149

(1) Assemble the crankshaft timing gears and front timing gear damper. (2) Turn the engine upside down on the overhaul stand. (3) Install the upper grooved main bearing shells in the block. If the old bearing shells are to be used again, install them in the same locations from which they were removed. The two wide bearing are installed at the ends of the cylinder block. (4) Apply clean engine oil 360 degrees around all the crankshaft bearing journals and install the crankshaft in place so the timing marks on the crankshaft timing gear and the idler gear match. (5) Install the upper halves of the crankshaft thrust washers on each side of the rear main bearing support and the doweled lower halves on each side of the rear main bearing cap. The grooved side of the thrust washers must face toward the crankshaft thrust surfaces. If the crankshaft thrust surfaces were reground, it may be necessary to install oversize thrust washers on one or both sides of the rear main journal. (6) Install the lower main bearing shells – no oil grooves – in the bearing caps. If the old bearing shells are to be used again, install the in the same bearing caps from which they were removed. (7) Install the bearing caps and lower bearing shells. Main bearing caps must fit tightly. If the bearings have been installed properly, the crankshaft will turn freely with all of the man bearing cap bolts drawn to the specified torque. (8) Check the crankshaft end play by mounting a dial indicator to the end of the crankshaft and moving the crankshaft toward the gage with a small (less than 12 inches) pry bar. Keep a constant pressure on the pry bar and set the dial indicator to zero. Then, remove and insert the pry bar on the other side of the bearing cap. Force the crankshaft in the opposite direction and note the amount of end play on the dial.

The end play should be 0.102-0.356 (.004-.014 in) with new parts or a maximum of 0.457 mm (0.018 in) with used parts. Insufficient end play can be the result of a misaligned rear main bearing or a burr or dirt on the inner face of one or more of the thrust washers. Crankshafts end should be checked again after the installation of the power take-off assembly, transmission, marine gear or generator.

Detroit 12V149 Piston Rings

If you need a rebuild kit or other parts, remember that Diesel Pro has you covered. The Detroit 149 series have this arrangement for the piston rings, going from the top to the bottom:

Top (fire) ring / Compression rings /Seal rings / Dome / Bushing / Piston Pin / Retainer / Skirt
Two Piece Oil Ring – Upper
Two Piece Oil Ring – Lower

When to Replace or Repair Detroit 149 Series Piston Components

Use this guide to determine if you need to make any repairs. Many of these can be repaired with a piston kit, or a repair kit, available here at
(1) Check the dome, to see if it is cracked or scored. If it is, then replace the dome.
(2) Are the bores on the dome burred? If yes, repair the dome.
(3) Is the skirt cracked or scored? If yes, replace the dome.
(4) Is the skirt diameter in limit? If it isn’t, then replace the skirt.
(5) Is the pin cracked or scored? If it is, replace the pin.
(6) If the bushing flaking or scored? If it is, replace the bushing.
(7) Is the cylinder liner out of round? If yes, replace the liner.
(8) Are the block bores out of round? If they are, repair the block.

Disassemble the Turbocharger Detroit 12V149

The turbocharger is one of the most important of the Detroit 12V149 parts. Prior to disassembly, mark related positions of the compressor housing, center housing and turbine housing with a punch or scribe, to make sure they are reassembled in the same position.

(1) Loosen the vee band coupling securing the compressor housing to the backplate assembly. Be careful when removing the compressor housing and turbine housing to prevent damage to the compressor and turbine wheels. (2) Depending on type of turbocharger, either: (a) bend down the ends of the lockplates and remove the eight bolts securing the four lockplates and turbine housing clamps to the center housing and turbine. (b) Loosen the vee band coupling securing the turbine housing to the center housing. (3) Remove the turbine housing. Tap only with a soft hammer force if needed. (4) Position the turbine wheel of the center housing assembly in a suitable holding fixture, to reduce movement. (5) Remove the wheel nut from the shaft. (6) Press the compressor wheel from the wheel shaft assembly. (7) Withdraw the wheel shaft assembly from the center housing. The wheel shroud that is not retained will fall free when the wheel shaft is removed. (8) On some turbos, remove and discard the turbine piston ring from the wheel shaft. (9) Bend down the lock tabs and remove the four bolts and lockplates securing the backplate assembly to the center housing and remove the backplate assembly. (10) Lightly tap the backplate to to remove it from the center housing recess. (11) Remove and discard the seal ring from the center housing groove. (12) Remove the thrust spacer and piston rings from the backplate assembly. Discard the piston rings. (13) Remove the three screws holding the thrust collar and thrust bearing to the center housing. Remove the thrust collar, inboard thrust washer, bearing, bearing washer, and snap ring from the center housing. Discard the thrust washer, bearing, washer and snap ring. (14) Remove the snap ring, bearing, bearing washers and snap ring from the opposite end of the center housing. Discard the snap rings, bearing and washers.

Inspect the oil feed lines for dents or crimping.
Check the bolts that they do not have nicked, crossed, or stripped threads.
Inspect the turbine wheel for rubbing or wear.
Inspect the shaft for scoring, scratches or bearing seizure.
Inspect the compressor wheel for rubbing or damage caused by foreign material. Make sure it is free of foreign material.

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