Usage:
Reference: GUIDELINE FOR REUSABLE PARTS, Valves And Valve Springs, Form No. SEBF8002-01.
Reference: GUIDELINE FOR REUSABLE PARTS, Valves and Valve Springs Specifications, SEBF8034-04.
Several questions have surfaced regarding the reusability of exhaust valves in cylinder heads reconditioned by dealers and Caterpillar Remanufacturing. The biggest contributor to the confusion, regarding exhaust valve reuse, are product problems. These product problems have a direct effect on customer perception of exhaust valve life. When dealers have problems with customer perception, they become "gun shy" and sometimes "over-repair".
Engine Division Engineering agrees that the life of an exhaust valve, under normal operating conditions, should be two engine life cycles. However, when an engine is operated with high exhaust temperatures, the life of the exhaust valve can be drastically reduced. In most cases, when a dealer reconditions a cylinder head for a customer in his territory, the dealer has some idea of the type of operating conditions the engine experienced and customer maintenance practices. Along with this information and the Reference material, the dealer can make a confident reuse decision. Under normal or typical operating conditions, where exhaust temperatures are not beyond the upper limit, exhaust valves should be reusable if they meet the current "Reference" specifications.
The Caterpillar Remanufactured Products Group started replacing exhaust valves, in remanufactured cylinder heads, across the board in September 1990. This was a decision based on dealer/customer concerns, regarding exhaust valve failures and that Remanufacturing didn't know the head history. Various dealers were replacing exhaust valves on all in house cylinder head rebuilds. Dealers also reported customers were requesting new exhaust valves be installed in reconditioned heads because of poor experience with exhaust valve life in reconditioned cylinder heads.
3500 Series Engineering recommends that all exhaust valves be replaced at rebuild, because operating temperatures can not be accurately identified by visual inspection. High exhaust temperatures may be related to aftercooler housing gasket leaks, loose turbocharger center housing band clamps, turbocharger failures, etc. Dealers can base exhaust valve reusability on history, customer operating conditions and site location. If the site is in high altitude, which results in higher than normal exhaust temperatures, the dealer should replace the exhaust valves at rebuild. Intake valves are replaced only if they do not meet the guidelines in the Reference material.
When rebuilding engines, the reusability of all of the cylinder head valves is a cost savings, and should be executed whenever possible. Caterpillar's position, with some exceptions, has always been and will be to recommend reusability of engine valves as per the Reference material.
Dealers have the advantage of the customer's equipment history. This can take some of the risk out of making reuse decisions. The history of a component, received by the Caterpillar Remanufactured Products Group is not known, so they take the positive quality approach, and replace all exhaust valves to prevent failures.