RING-RETAINING 7D6705 - Caterpillar

627B (PP),
637D, 637D (PP) And 639D ScrapersSUPPLEMENT: 05/23/83SERVICE MAGAZINE, MARCH 14, 1983, PAGE 3.In the article "Operation Of Scraper Engine Governor Control Valve", change the Form SENR2765 to read SENR7265.--------------- END SUPPLEMENT ---------------Some changes are needed in the Service Manual modules, Tractor-Scraper Air System And Brakes, Form SENR2592, SENR2765, and SENR2018. Some of the information is not correct in the topic Governor Control Valve For The Scraper Engine. The 3S5254 (for 627B) and 2G8774 (for 637D, 639D) Throttle Control Valves do not supply full system air pressure to the scraper engine rotochamber. The throttle control valve controls the air pressure from no pressure at engine off or low idle speed up to a maximum range of 220 to 250 kPa (32 to 36 psi). At air pressures between 0 and 220 kPa (0 and 32 psi), the engine will run at that respective speed between low idle and high idle.
If the engine will not operate at the high idle speed given in the specifications, make the checks that follow.
1. Check the air pressure at the delivery port on the throttle control valve and make sure the operation of the valve is correct.2. If the valve operation is correct, check the air pressure at each junction of the air line from the throttle control valve to the scraper engine rotochamber.