The chart below shows the most common questions asked by owners of Detroit Diesel® engines 8V71 Natural when trying to troubleshoot why their engines underperform.  It categorizes areas of possible malfunction, likely cause and recommended action to bring your new, rebuilt or used  Detroit Diesel® engine back to proper operation.  The chart will give you confidence when speaking with your Detroit Diesel® engine mechanic or ordering parts.  As a quick reference guide only, the chart must not be thought of as a substitute for the use of your Detroit Diesel® engine 8V71 Natural Owner's operating or service manual.

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Detroit Diesel 8V71 Usefull Information 

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For the Detroit 8V71, the serial number will have an 8VA in the beginning. An example of what the serial number would look like for this engine series is 8VA-234567.

The model number, on the other hand, will be an eight digit number separated by a dash. For the natural or non-turbo engines, the model number would be 7 0 8 x – x 2 x x. For the turbo engines, the model number like 7 0 8 x – x 3 x x.

The first three digits will always be 708 for this engine. The fourth digit will signify the application, such as 2 for marine use, 3 for industrial use and so on. The fifth digit refers to the engine arrangement. Some engines have the starter opposite of the oil cooler, where others will have these two on the same side. Likewise, the rotation of the engine can vary from engine to engine. The sixth digit indicated whether the engine has a two valve head (1) a four valve head (2) or a turbocharger (3). The last two further indicate the specific model.

The Detroit 8V71 engine has been used in many applications, including GMC vehicles, Chamberlain Tractors, heavy equipment, Semi-Trucks and many more. This engine may also be called the following. To clarify, all of the parts here will work with the following:

• 8V-71 or 8V 71

• GM 8V71


Specs and Normal Values

This engine has a displacement of 567.5 cubic inches.

At 1200 RPM, the following are the normal values:

• Oil pressure: 40-55 PSI
• Air box pressure: 1.1 Inches Mercury
• Fuel Pressure at Cylinder Head: 40-60 PSI

At 2100 RPM, the following are normal values:

• Oil pressure: 50-70 PSI
• Air box pressure: 5.5 Inches Mercury
• Fuel Pressure at Cylinder Head: 40-60 PSI

The Coolant temperature should be between 160 and 185 degrees F and the lubricating oil temperature should be between 200 and 235 for any speed between 1200 and 2100 RPM.


Changing the Fuel Pump

Here we offer some maintenance tips for the 8V71 Detroit Diesel. Please note that these are meant to be a general guide only, and that more intensive repairs should always be performed by an experienced Diesel Mechanic. Please be sure to note the location of any part before removal, to make reattachment quicker and easier, and to make sure the engine will continue to function as it should.

The fuel pump is very important to the operation of the engine. The pump keeps the air out of the system, and is driven by the blower motor, and will always rotate to the left for the 8V71.

To begin, look at the two tubes running into the pump, which should be towards the rear of the engine, where it is driven by the right-hand blower rotor. There you will see the pump, underneath the governor housing, which is attached to the pump by three bolts and copper seals. The shaft for the fuel pump is driven by a coupling disc attached to the blower.

The pump cover will have two dowels in place to keep the cover in the proper position, and does not need a gasket. When this is removed, you will see two gears, one being the driven gear (attached to the driven shaft) and the drive gear (attached to the drive shaft.) The drive gear will have a small steel ball located near the shaft. On the bottom of the pump body will be two holes, which you can attach a hose to in order to capture any leakage. You will also see a spring loaded valve, which is designed to relieve any excess pressure in case the filter is clogged. This should happen at around 70 PSI pressure.

To service the 8V71's fuel pump, follow these steps:

Step One: Disconnect all of the tubes that may contain fuel, including the inlet, outlet, and drain tube.

Step Two: Remove the three bolts and remove from the governor housing. This is a good time to check the coupling fork, an example of which can be seen here: 8V71 Coupling Fork

Step Three: Remove the eight bolts on the cover of the pump, and remove it. Be sure to protect the face of the pump cover and body from any damage.

Step Four: Remove the drive shaft, drive gear and the retaining ball from the rest of the pump body. Then press the shaft enough to remove the retaining ball.

Step Five: Press the shaft away from the gear, making sure not to press the squared end of the shaft through the gear.

Step Six: The driven gear and its shaft can now be removed. However, these pieces should remain together after removing from the rest of the pump.

Step Seven: Hold hand on relief valve plug, to reduce the tension on the spring. The valve spring, pin and the valve can then be removed.

Step Eight: If you need to replace the seals it can be done here. Clamp the pump to a vise-grip, and screw threaded end of the tool into the seal closest to the bolting flange. Tap the end to remove the seal, making sure to replace the seal as it was before removal.

Step Nine: Check for any scoring along the gear teeth, the drive and drive shafts. Check the faces of the pump body to make sure it is smooth and not warped. The relief valve as well should be free of any visible damage.

Step Ten: To reassemble, lubricate the lips of the seal with vegetable shortening, and replace any seals in the direction of which it was removed.

Step Eleven: Lubricate and replace valve. Install the fuel pump drive gear over the drive shaft (not the squared end.) Press the gear past the ball detent (slot for the ball.) Then place the ball in the detent and press the gear back until it comes in contact with the ball.

Step Twelve: Lube the pump shaft and insert the square end into the pump body, through the oil seals. Place the driven shaft and gear assembly back in the pump body.

Step Thirteen: Apply sealant on the pump cover, then place the cover back on the body. Reattach the eight bolts and finish assembly. Rotate the pump shaft to make sure everything moves freely.