Some Tips on the Lycoming O-235 Engine

Little things are sometimes forgotten so a reminder is sometimes necessary. In the case of the Lycoming O-235 engine, it is a little different from most other Lycoming models. Other models are equipped with hydraulic tappets which do not require frequent adjustment. Occasionally, there is a report of an O-235 which is running rough or not producing normal power. Investigation often reveals that the solid tappets of the O-235 need adjustment. The Lycoming Operator’s Manual states that valve rocker clearance should be checked, and reset if necessary, at each 100-hour inspection. We find that since this engine model is a little different, this inspection item is often overlooked. This reminder may help operators of the O-235 engine to keep it running smoothly.

A second problem sometimes reported with the O-235 engine also is the result of it being just a little different from other Lycoming models. Some O-235 engines which use a full-flow oil filter have had very 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 was traced to improper installation of the oil filter adapter. 

These instructions specify that for the O-235 engine only, a plate – Lycoming Part Number LW-12999 – is to 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. When this plate is not installed as required, it results in the oil pressure discrepancy discussed earlier. Anyone who has occasion to install the oil filter kit after overhaul – or at any other time, should follow the instructions carefully and should consider that the O-235 installation is slightly different from other Lycoming models.

However, the O-235 engine is certainly not an eccentric problem creator. When the engine is maintained and operated in accordance with manufacturer instructions, it is so reliable that many models became eligible for an increase in TBO from 2000 to 2400 hours. Owners of O-235 engines built before mid-1986 may want to examine more closely. Starting in June of 1986, 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 individuals 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.

Those O-235 models with a compression ratio of 6.75:1 were immediately eligible for the 2400-hour TBO if they contained 100% Geniune Lycoming parts. For those owners who have maintained their engine reliability and durability by using only Lycoming parts, this notification of increased TBO was good news.