[FONT="]From Sacramento Sky Ranch:
[/FONT]
[FONT="]
[/FONT]
[FONT="]Checking and Adjusting Dry Tappet Clearance on Lycoming Aircraft Engines[/FONT]
[FONT="]Any time work is done on the valve train of an engine, such as grinding valves or seats, replacing valves or valve rockers, or any other component of the valve operating mechanism, dry tappet clearance should be checked and adjusted to insure that the correct tappet clearance is maintained. If tappet clearance varies too far from prescribed limits, the engine will not operate properly. For example, if clearances are too small, burned valves or compression loss may result; if clearances are too great, the engine will be noisy. In both cases, mechanical failure may be the end result. [/FONT]
[FONT="]After observing all safety precautions, rotate the engine until the piston is on top dead center of the cylinder to be checked.
(1) Remove the rocker box cover, and also remove rocker shaft covers on angle-head cylinders, valve rockers, thrust washer (angle-head only), push rods, and shroud tubes. [/FONT]
[FONT="](2) Remove hydraulic unit from the tappet body. On TIO541 and TIGO541 engines remove the unit with fixture ST-233. On all other engines use special tool Part No. 64941, that can be purchased from Lycoming, or fabricate a puller from a piece of wire. NO MAGNET PLEASE. [/FONT]
[FONT="](3) Disassemble the hydraulic unit and flush out all oil from the unit. Remove all oil from the tappet body. [/FONT]
[FONT="](4) Re-assemble hydraulic unit and install in the tappet body. CAUTION: Be sure to keep hydraulic units as one assembly because mixing hydraulic unit parts may result in changing the leak down rate of the unit and may cause a rough operating engine. CAUTION: After cleaning the hydraulic unit and tappet body, and unit is installed in the engine, do not turn the prop because this pumps oil into the hydraulic unit and results in an inaccurate dry tappet clearance check. [/FONT]
[FONT="](5) Next, replace the shroud tubes using new seals. [/FONT]
[FONT="](6) Install push rods, valve rockers, and thrust washer on angle head cylinders only. [/FONT]
[FONT="](7) To check dry tappet clearance, depress hydraulic unit by pressing on the push rod end of the rocker, and measuring the clearance between the valve stem and heel of the rockers by using a feeler gage. On engines using rotators on the valves, clearance is measured between the rotator and the heel of the rocker. In both cases, the clearance should be .028 to .080 on intake and exhaust valves on all engines except the TIO541 and TIGO541 series aircraft engines; the latter should be .040 to .105. If clearance falls within these limits, no adjustment is necessary. If not, then adjust to within limits in the following manner: If clearance is too great - remove the push rod and install a longer one. If clearance is too small - install a shorter push rod and recheck to be sure clearance is within limits. To determine a short push rod from a long one, check the part number on the end of the push rod. The lowest number is the shortest rod, and the highest number is the longest rod. On older type push rods, machined grooves are found on one side of the push rod, three grooves represent the short rod, and no grooves represent the long rods. Consult Lycoming Service Instruction No. 1060, and applicable parts catalog[/FONT]
[/FONT]
[FONT="]
[/FONT]
[FONT="]Checking and Adjusting Dry Tappet Clearance on Lycoming Aircraft Engines[/FONT]
[FONT="]Any time work is done on the valve train of an engine, such as grinding valves or seats, replacing valves or valve rockers, or any other component of the valve operating mechanism, dry tappet clearance should be checked and adjusted to insure that the correct tappet clearance is maintained. If tappet clearance varies too far from prescribed limits, the engine will not operate properly. For example, if clearances are too small, burned valves or compression loss may result; if clearances are too great, the engine will be noisy. In both cases, mechanical failure may be the end result. [/FONT]
[FONT="]After observing all safety precautions, rotate the engine until the piston is on top dead center of the cylinder to be checked.
(1) Remove the rocker box cover, and also remove rocker shaft covers on angle-head cylinders, valve rockers, thrust washer (angle-head only), push rods, and shroud tubes. [/FONT]
[FONT="](2) Remove hydraulic unit from the tappet body. On TIO541 and TIGO541 engines remove the unit with fixture ST-233. On all other engines use special tool Part No. 64941, that can be purchased from Lycoming, or fabricate a puller from a piece of wire. NO MAGNET PLEASE. [/FONT]
[FONT="](3) Disassemble the hydraulic unit and flush out all oil from the unit. Remove all oil from the tappet body. [/FONT]
[FONT="](4) Re-assemble hydraulic unit and install in the tappet body. CAUTION: Be sure to keep hydraulic units as one assembly because mixing hydraulic unit parts may result in changing the leak down rate of the unit and may cause a rough operating engine. CAUTION: After cleaning the hydraulic unit and tappet body, and unit is installed in the engine, do not turn the prop because this pumps oil into the hydraulic unit and results in an inaccurate dry tappet clearance check. [/FONT]
[FONT="](5) Next, replace the shroud tubes using new seals. [/FONT]
[FONT="](6) Install push rods, valve rockers, and thrust washer on angle head cylinders only. [/FONT]
[FONT="](7) To check dry tappet clearance, depress hydraulic unit by pressing on the push rod end of the rocker, and measuring the clearance between the valve stem and heel of the rockers by using a feeler gage. On engines using rotators on the valves, clearance is measured between the rotator and the heel of the rocker. In both cases, the clearance should be .028 to .080 on intake and exhaust valves on all engines except the TIO541 and TIGO541 series aircraft engines; the latter should be .040 to .105. If clearance falls within these limits, no adjustment is necessary. If not, then adjust to within limits in the following manner: If clearance is too great - remove the push rod and install a longer one. If clearance is too small - install a shorter push rod and recheck to be sure clearance is within limits. To determine a short push rod from a long one, check the part number on the end of the push rod. The lowest number is the shortest rod, and the highest number is the longest rod. On older type push rods, machined grooves are found on one side of the push rod, three grooves represent the short rod, and no grooves represent the long rods. Consult Lycoming Service Instruction No. 1060, and applicable parts catalog[/FONT]
