Usage:
All Caterpillar Products Equipped With Piston-Type Pumps And/Or Motors
Reference: "Maximum Permissible Rates For Case Drain Leakage Permit Field Checks Of Piston-Type Hydraulic Pumps And Motors," Service Magazine, September 1, 1980, Page 3.
The reference article gives maximum rates of case drain leakage for field tests of piston-type hydraulic pumps and motors. Leakage rates higher than those shown in the chart are not positive indications of a failure, but they are an indication of an existing problem.
One possible cause of this internal leakage is a warped (twisted) port plate.
If too much case drain is a problem, check the port plate to find if it is warped. With the port plate in position on the barrel, use a feeler gauge to check for clearance between the port plate and the barrel. If there is clearance, the port plate can be lapped to make it flat. No more than 0.13 mm (.005") of material can be removed from the plate. If it is necessary to remove more than 0.13 mm (.005") to make the plate flat, install a replacement plate. Be sure to check the replacement plate before it is installed.
If over 0.03 mm (.001") of material must be removed, use a lapping plate with 20 micron silicone carbide lapping compound and oil to work the plate. During the procedure, check the plate several times to make sure the complete surface has been lapped.
After the complete surface has been lapped with the 20 micron compound, use the "touch lapping" procedure to finish lap the plate. Also, use this procedure if less than 0.03 mm (.001") of material must be removed from the plate. The "touch lapping" procedure is shown in "Guideline For Reusable Parts, Piston Pumps and Motors," Form No. SEBF8032. If possible, check the surface finish. It must be approximately 0.2 micrometer (8 microinches).
If a port plate appears to be flat use the touch lapping procedure to make sure.