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Mitsubishi 3000GT Engine Assembly (6G72 DOHC)

This guide covers the assembly of the Mitsubishi 6G72 DOHC V6 engine (naturally aspirated or twin-turbo). This engine was used in the 1991-1999 Mitsubishi 3000GT/GTO and 1991-1996 Dodge Stealth.

Note: The 6G72 SOHC variant is significantly different in construction despite having the same engine code and is not covered by this guide.

The factory procedure and specifications will be used to assemble the cylinder block, crankshaft, connecting rods, pistons, cylinder heads, valvetrain, and camshafts into what is known as a "long block". If you are using aftermarket or upgraded internal components, please consult your local machine shop or engine builder for the correct assembly specifications for those components.

Tools (12)

Parts (2)

Step-by-step instructions

Step 1 · photo 1Step 1 · photo 2
1

Assembly Tips

  • Clean and inspect all parts, removing paint, rust, gunk, and grit. This is very important for internal components.
  • Reusing worn or damaged parts may result engine failure. Your local machine shop or engine builder can usually recondition worn parts rather than replace them.
  • Assemble the engine in a clean and dust free work area. Place oiled parts on a lint-free rag to avoid picking up debris from the work surface.
  • Use a tap to clean out threads before assembling parts.
Step 2 · photo 1Step 2 · photo 2
2

Cylinder Block

  • Use a cylinder hone and drill to prepare the cylinder walls. First clean the walls, then lubricate with diesel fuel or engine oil before honing.
  • Vary the drill speed and up/down motions to achieve a 30 degree cross hatch pattern on the walls.
  • This process removes any glazing and restores the correct surface finish needed for the piston rings to seal.
  • Make sure to clean the cylinder walls and remove all grit created by the honing process.
Step 3 · photo 1Step 3 · photo 2
3
  • Install the following expansion plugs using a socket and hammer:
  • One 41.5mm plug (right side)
  • Two 35mm plugs (rear)
  • Five 25mm plugs (left and right sides)
Step 4 · photo 1Step 4 · photo 2Step 4 · photo 3
4
  • Install the two threaded hex plugs (front and rear) using an 8mm hex wrench.
  • Install the two threaded coolant plugs (left and right side) using a 14mm wrench.
  • Apply sealant or pipe tape to the plug threads.
Step 5 · photo 1Step 5 · photo 2Step 5 · photo 3
5
  • This step is for turbo engines only.
  • Install the six oil squirters into the angled holes in the main bearing journals using a punch and hammer.
  • Make sure each oil squirter is fully seated and below the bottom of the oil feed groove.
  • Do not install oil squirters in the center oil feed holes.
6

Crankshaft

  • Install the main bearings into the block and girdle.
  • Install the grooved bearings in the block side.
  • Make sure the journal surfaces underneath are clean and dry.
7
  • Carefully install the crankshaft into the block.
  • Make sure the bearings are clean and dry.
  • Do not rotate the crankshaft after it is installed.
  • Add a small length of Plastigauge to each bearing journal.
  • Carefully set the girdle onto the crankshaft. Line it up perfectly with the bearing journals on the block.
  • The girdle fits very tightly into the block and will not be fully seated until the next step.
8
  • Apply engine oil to the main bolt threads and underside of the head.
  • Do not dip the bolt in engine oil. Too much oil may damage the block.
  • Install the main bolts. Evenly tighten until snug using a socket wrench and 17mm socket.
  • Tap the girdle with a soft-faced hammer while continuing to snug the main bolts until the girdle is fully seated.
Step 9 · photo 1Step 9 · photo 2
9
  • Install the main cap bolts and tighten them by hand.
  • Two-bolt blocks will have eight bolts total.
  • Four-bolt blocks will have 16 bolts total.
  • Use a torque wrench and a 17mm socket to tighten the main bolts to the specified torque:
  • Two-bolt blocks: 67 ft-lbs (93 Nm)
  • Four-bolt blocks: 54 ft-lbs (74 Nm)
  • Tighten bolts in the sequence shown.
10
  • Loosen the main bolts and carefully remove the girdle.
  • Measure the width of the Plastigauge to determine the bearing clearance of each journal.
  • Main bearing clearance should be ***0.0008-0.0020 in (0.020-0.050 mm)***.
  • Do not continue if bearing clearances are out of spec. Double check that the main bearings, crankshaft, and girdle are installed correctly and that the crankshaft isn't excessively worn.
11
  • Remove the crankshaft.
  • Apply assembly lube to the smooth side of the thrust washers.
  • Stick the thrust washers onto the sides of the #3 journal on both the block and girdle.
  • The thrust washer grooves face away from the bearing journals.
  • Apply assembly lube or engine oil to the main bearings and thrust washers.
12
  • Reinstall the crankshaft and girdle.
  • Be careful not to knock the thrust washers out of position.
  • Reinstall the main bolts and repeat Step 8.
13
  • Spin the crankshaft one complete rotation. It should spin smoothly throughout.
  • Attach a dial indicator to the nose of the crankshaft to measure end play.
  • Use a large flathead screwdriver to carefully move the crankshaft side to side. Zero the indicator at one extreme, then take a measurement at the other extreme.
  • Crankshaft end play should be ***0.0020-0.0098 in (0.050-0.250 mm)***.
  • Do not continue if the end play is out of spec. Double check that the thrust washers are installed correctly and of the correct thickness.
14
  • This step is for two-bolt turbo engines only.
  • Install the four girdle side stays.
  • One stay is shaped differently and goes in the front-right position.
  • Install the eight side stay bolts. Apply engine oil to the threads and underneath the bolt head.
  • Do not dip the entire bolt in engine oil. This may damage the block.
  • Use a 14mm wrench to snug all bolts.
  • Use a torque wrench and 14mm socket to tighten the girdle-side bolts, followed by the block-side bolts.
  • The torque is 35 ft-lbs (48 Nm).
15

Install Valvetrain

  • Insert wisdom here.
16

Install Heads

  • Insert wisdom here.
17

Install Camshafts

  • Insert wisdom here.
18

Check Camshaft Bearing Clearance

  • Insert wisdom here.
19

Long Block

  • Install the head gaskets on the cylinder block.
  • Install heads onto block, being careful the head gasket stays in position.
  • Install head bolts and hand tighten.
Step 20 · photo 1
20
  • Use a torque wrench to tighten the head bolts in three even steps:
  • N/A Engines: 26, 52, 80 ft-lbs (36, 72, 110 Nm)
  • Turbo Engines: 30, 60, 90 ft-lbs (41, 82, 125 Nm)
  • Tighten all bolts to the specified torque before increasing to the next torque step.
  • Tighten bolts in the sequence shown.

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