The Lycoming O-235 engine is a little different than the other Lycoming engines. While other models are equipped with hydraulic tappets which do not require frequent adjustment, the solid tappets of the O-235 need adjustment more frequently. At each 100-hour inspection, it is reccommended that the valve rocker clearance should be checked and reset if necessary. This step is one that is often overlooked with the O-235 model, but it is vital to keep your Lycoming engine running smoothly! Consistent aircraft engine maintenance is necessary to keep your engine running smoothly and safely.
Another recommendation for your Lycoming O-235 is to understand that some O-235 engines with a full-flow oil filter have a possibility of low oil pressure at idle after being overhauled. The oil pressure would then increase as power was increased and decrease as power was reduced. This inconsistency from the normal oil pressure indications is typically caused by improper installation of the oil filter adapter. When this plate is not installed as required, it results in the oil pressure discrepancy.
For the O-235 engine, a plate – Lycoming Part Number LW-12999 – should be installed between the accessory housing and the oil filter adapter. The plate is sandwiched between two gaskets – Lycoming Part Number LW-12795. The plate is designed with a hole that meters the amount of oil flow and prevents an excessive flow of oil to the idler gear.
While the O-235 engine is built a bit different than the other Lycoming models, these differences are no cause for alarm. When the engine is maintained and operated in accordance with manufacturer instructions, the reliability makes it so that the engine can increase in TBO from 2000 to 2400 hours!
What happened in June of 1986 is that all new, remanufactured and factory-overhauled O-235 engines with compression ratios of 8.5:1 or 8.1:1 are built with new increased-strength pistons, Part Number LW-18729. This part change, together with past service history, will allow Lycoming to increase the recommended TBO from 2000 hours to 2400 hours.
For those who own an O-235 with 8.5:1 or 8.1:1 compression ratio, a TBO Extension Kit is available. The kit includes four new pistons and all other parts necessary for the change. It should be noted that the TBO extension may only be applied to those engines that contain 100% Genuine Lycoming parts! The O-235 models with a compression ratio of 6.75:1 are eligible for the 2400-hour TBO if they also use the Genuine Lycoming parts.