Usage:
769C, 773B, 777 Trucks
Reference: SERVICE MAGAZINE, NOVEMBER 29, 1982 article "Dump Body Exhaust Port Can Be Moved".
Modifications can be made to improve the distribution of exhaust through the truck dump body ribs. The use of exhaust to heat the dump bodies on 769C, 773B and 777 Trucks prevents material from freezing to the dump bodies during cold weather. In some applications, exhaust heat allows sticky materials to be dumped more easily.
Use the following procedure to improve the distribution of exhaust through the truck dump body ribs.
1. Check the rear rail to make sure that material has not blocked the exhaust flow from the left side of the dump body. See Reference Article.
2. Check to make sure that equal heating of both sides of the dump body is obtained. If the heating is not equal, a fabricated baffle should be installed to equalize the exhaust flow between the right and left sides of the dump body. Illustration 1 shows the basic design of the baffle, and Illustration 2 shows where to install it. It may be necessary to install baffles of various sizes to obtain equal exhaust flow.
Illustration 1. Dimensions for baffle.
Illustration 2. Correct installation of baffle.
After the baffle has been installed, check to make sure that the exhaust restriction does not exceed 6.7 kPa (27" H2O). The restriction should be measured at the frame-mounted exhaust elbow. Drill and tap the elbow to accept the fitting for an appropriate gauge. Measure the restriction while the dump body is down. Plug the elbow after measuring the restriction.
Another indication of excessive restriction is high exhaust temperature ahead of the turbochargers. The exhaust temperature should never exceed 650°C (1200°F) ahead of the turbocharger. The temperature can be checked with the 6V6125 Infrared Thermometer.
3. Some machines are equipped with exhaust diverter valves which pass one-third of the exhaust through the mufflers when the dump bodies are down. This keeps the temperature of the muffler and the exhaust piping high to prevent thermal shock when the dump body is raised.
Check the operation of the exhaust diverter. Special Instruction, Form SMHS7608, "Installation of Engine Exhaust Diverter Valve and Muffler," has operation check and adjustment information. Be sure the valve is closing properly when the dump body is down.
Also, the bypass flow may be sufficient to reduce body heating. If this condition is determined, some holes in the muffler tube in the diverter can be welded shut.
NOTE: The effect on the service life of the muffler and the exhaust piping is not known. Shortened service life may result.