Hydraulic lifters passing visual inspection should be tested for leakdown. A special leakdown tester is used for this operation. Test results are determined by length of time in seconds required before the tester overcomes the hydraulic pressures in the lifter. Normal leakdown range is between 20 and 90 seconds. Always refer to the manufacturer's specifications. A lifter that fails the first leak-down test should be retested since air may be trapped in it. If the test results indicate a failure or marginal result, replace the lifter.
To perform a leakdown test:
- Fill the cup with enough fluid to cover the lifter and place the lifter into the fluid.
- Position the tester ram into the pushrod seat of the lifter, making sure the ram is centered.
- Adjust the ram length until the pointer aligns with the set mark on the lever and tighten the jam nut.
- Pump the weight arm to move the lifter through its entire range of travel. This is done to purge air from the lifter.
- Continue to pump the lifter until a resistance if felt.
- Raise the arm to return the lifter to its full height, then lower the ram onto the pushrod seat.
- Time how long it takes for the weight to compress the lifter.
- During the test, turn the hand crank on the tester so the cup rotates at a rate of one turn every two seconds.