Engine Pushrods

Editorial Staff

Monday, July 26, 2021 at 10:11 AM ET

Verified

Key Takeaways:

Multiple aircraft experienced failures or significant wear in pushrods and rocker arms, ranging from abnormal wear to breakage.
A common underlying cause for these issues was insufficient lubrication, often due to oil starvation or a lack of oil reaching critical components.
Incidents led to various operational problems, including engine roughness, metal contamination in oil, failed compression checks, and internal engine damage, with some cases involving stuck valves or suspected design flaws.

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Cessna 172N Skyhawk

Broken Pushrod

The #3 cylinder exhaust valve pushrod broke due to a valve stuck in the closed position. No marks were seen on the top of the piston through a borescope. The lifter came apart as a result of the broken pushrod but appears to have been operating properly previously.

Part total time: 1567.0 hours

Cessna 172S Skyhawk SP

Abnormal Wear

During an unscheduled inspection, the #2 cylinder intake pushrod and rocker arm were found abnormally worn. (They were replaced 64.7 hours earlier.) The #3 cylinder exhaust pushrod and rocker arm also were abnormally worn.

Part total time: 64.7 hours

Cessna 172S Skyhawk SP

Excessive Wear/Oil Starvation

Due to a failed compression check on the #2 cylinder, a defective rocker arm and pushrod were discovered. All rocker arms and pushrods were subsequently inspected and excessive wear found. Defects appear to be due to oil starvation.

Part total time: 1117.0 hours

Cessna 402C Utililiner

Broken Pushrod

Pilot reported the left engine running rough in flight and oil pressure at zero. Inspection found metal contamination in oil filter, #4 cylinder intake push rod broken and a large gap at the exhaust rocker arm. The engine was replaced and sent to the manufacturer for analysis.

Part total time: 168.0 hours

Piper PA-28-181 Archer II/III

Extremely Worn Pushrod Ends

Customer reported trace metal in oil filter. Cylinders were removed from engine, and extreme wear was found on the pushrod ends and the rocker arm sockets. This wear seems to be a design flaw on Lycoming’s new-style roller tappet engines. It appears that not enough oil is reaching the top of the cylinders and the rocker arms.

Part total time: 565.0 hours

Piper PA-31-350 Navajo

Bent Pushrod

A few miles from the airport, the #2 engine began to run rough; the pilot performed a precautionary shutdown. Inspection revealed the #6 cylinder intake tube and pushrod were bent. While attempting to change the cylinder, it was determined to be damaged to the point of not being able to be removed from the crankcase. The #4 cylinder was removed and borescope inspection found a #6 connecting rod failure and internal damage.

Part total time: 1741.0 hours

Piper PA-44-180 Seminole

Abnormal Wear

During visual inspection, both engines’ rocker arms and the right engine #3 cylinder exhaust pushrod showed abnormal wear at rocker arm end.

Part total time: 1044.0 hours