Thursday, June 30, 2016

Checking Hydraulic Valve Tappets After Oil Purge Procedure

After performing the purging of the oil system, the hydraulic valve tappets need to be checked to make sure they have pumped up with oil. The hydraulic valve tappet is built into the lower portion of the valve rocker arm. To perform the check, the lower spark plugs are removed and the valve cover for the cylinder being tested is removed. The valve cover is held onto the cylinder head by one M6 screw that is removed with a 5 mm hex wrench. A little bit of caution needs to be exercised when removing the valve cover to insure the rubber O ring on the screw comes off with the valve cover. The larger O ring around the perimeter of the valve cover will typically stay in place on the valve cover but sometimes the tiny O ring around the bolt can stick to the cylinder head and later fall off ... so it is important to verify that it is still on the bolt when the valve cover is removed.
The valve cover has a large gasket around the perimeter of the cover and a much smaller O ring on the M6 bolt as can be seen in the photo.

The test consists of pushing on the LOWER portion of the rocker arm to make sure it feels solid and there is only approximately a .020  gap between the rocker arm and valve stem. A hard plastic dead blow hammer was used to push on the lower portion of the rocker arm. Because the purge was done the day prior the first cylinder tested did not pass the test. I figured this was likely because the oil had time to drain away overnight so the valve cover was reinstalled and the propeller was rotated vigorously for a minute … then the valve cover was removed and the test was repeated, this time with success. Pushing on the lower portion of the rocker arm with the dead blow hammer handle just rocked the fuselage and the valve tappets did not collapse.
Using the handle of a plastic dead blow hammer to press on the LOWER portion of the rocker arm to verify the built in lifter is pumped up and can hold pressure.

The same procedure was used on the remaining cylinders and there were no valve tappets that failed the test. After the testing was completed, the hex nuts on the valve covers were torqued to 90 inch pounds.
Torqueing the M6 bolt on the rocker arm cover to 90 inch pounds.

At this point the oil system is ready for an engine start.