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These engines were first produced in the mid-1980s and have been used in several applications. The 6BT has established a reputation for power, and was used in the automotive market, including some Dodge pickup trucks. The very similar 4BT is a slightly smaller engine could be found in some industrial vehicles, including Chevy vans, as well as industrial equipment and marine engines. This four cylinder engine is known for its ability to deliver high power despite its relatively small size.

To identify your engine, check the dataplate on the engine for the model.

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General Information and Specifications for 4BT Parts 

The displacement is 3.92 liters for the 4B and 5.88 liters for the 6B.

The intake valve adjustment is 0.010 inch.

The exhaust valve adjustment is 0.020 inch.

The engine weight for the 4BT is between 715 to 770 lbs.

The engine weight for the 6BT is between 910 to 970 lbs.

Normal oil pressure, idle: 10 psi.

Normal oil pressure, rated speed: 30psi (minimum)

Oil capacity 4BT: 10 to 11.6 quarts (9.5 to 11 liters)

Cooling system capacity, 4BT: 7.4 quarts (7 liters)

Oil capacity 6BT and 6BTA: 15 to 17.3 quarts (14.2 to 16.4 liters)

Cooling system capacity, 6BT: 9.5 quarts (9 liters)

Cooling system capacity, 6BTA: 10.5 quarts (9.9 liters)


Cylinder Block Information

The six cylinder Cummins 6BT and 6BTA share many parts with the four cylinder 4BT, with the only key differences being the number of items related to the pistons, liners, or other items that are dependent on the number cylinders. Vibration dampers are only located on the six cylinder engines.
• Camshaft bushing bore must be between 2.130 and 2.1317 inches.
• Camshaft gears must be replaced if the root of the teeth show any signs of cracks or pitting.
• The proper ring gap information is as follows: Top (Turbo) 0.016 to 0.028 inches. The top ring for naturally aspirated engines is 0.010 to 0.022 inches. The intermediate ring is 0.010 to 0.022 inches. The oil control ring is between 0.010 to 0.022 inches.


Cylinder Head Information

The 6BT and 4BT Cummins are equipped with a one piece cylinder head with either 8 or 12 valves, or two per cylinder. The following are signs that certain related parts need to be replaced.
• Cracks, irregularities or guttering on combustion face.
• Wear on the heads and stems of the valve, such as scratches or streaks, a tip that is not flat, or any signs that it is bent.
• Signs the head is not flat, when using a feeler gauge, the end-to-end value is 0.012 inches for the 6B and 0.008 inches for the 4B. The side to side value cannot exceed 0.003 inches.
• The valve seat has any signs of cracks.


Injectors, Rocker Lever Assembly General Information

The following are signs that the rocker lever or injectors need to be replaced.
• The bore and contact surfaces of the valve stem show wear, such as cracks.
• The tappet face has pits that are over 2 mm in size.
• Push rods should be easily rolled when placed on their side. If they are bent, or cannot easily rolled then they should be replaced.
• Fuel lines are cracked at the ends.


Lubricating and cooling systems

These are area to check when you are working on the oil system or air intake system.
• The oil lube gears are cracked or have signs of wear.
• The water pump does not rotate freely or has damaged impeller blades.
• Thermostat has a broken spring, or does not start to open at 181 degrees F. It should be fully open at 203 degrees F.


Replacing a turbocharger

If you need to change the turbocharger on your 6BT or 4BT Cummins engine, use these steps as a general outline of the procedure.
• Remove the oil supply line from the turbo and oil filter.
• Using an 8mm screwdriver, remove the air crossover tube.
• If it is an automotive engine, locate the v-band clamp and hose clamp to remove the charge air cooler inlet.
• Using a 10 mm wrench, locate and remove the drain tube from the bottom of the turbo.
• Using a screwdriver, locate the clamp that keeps the drain line in place and remove it.
• Using a 15 mm wrench, remove the mounting nuts, gasket (and all gasket material) along with the turbocharger.
• To install a new turbo, first place the gasket in place and anti-seize compound to the mounting studs.
• Attach the turbo to its mount, using a 15 mm wrench tighten the bolts to 33 ft•lb.
• If needed, loosen the housing of the turbine and place the drain tube in position.
• Using a 13 mm wrench, install the clamps and hose on the drain tube followed by the drain tube and gasket. Tighten to 18 ft•lb.
• Attach the drain tube with sealant and gently tap into place. Connect the drain hose to the drain tube and screw the clamps to tighten.
• Tighten the housing capscrews using a 13mm wrench to 15 ft•lb.
• If needed, loosen the v-band clamp on the compressor housing to align it with the air crossover tube.
• After tightening the band clamp with a 7/16 inch wrench, tap it with a plastic hammer and tighten again to 75 in-lb.
• Install the air crossover tube with the clamps and tighten.
• Locate the tube for the boost control capsule actuator and attach.
• Pour 2 to 3 ounces of clean engine oil into the inlet.


Replacing an oil pump

This is a general guide for replacing a fuel pump on the 6B and 4B Cummins oil pump. Any major repairs should only be performed by an experienced Diesel mechanic.
• Using a 13 mm wrench, remove the pump by removing the four bolts holding it in position.
• Prepare the new lube pump by lubricating and filling it with clean engine oil.
• Line up the idler gear pin so the pump aligns up with the cylinder block.
• Tighten the capscrews with a 13 mm wrench to a torque of 18 ft•lb. Tighten the top inner screw first, then the outer bottom screw, then the outer top screw and finally the inner bottom screw.