Q: I recently purchased a high hour O-320-A1A in an RV-3. The rocker arms were out of limits and I had them rebushed and sized.
The description for the exhaust valve is confusing on Lycoming Service Instruction No. 1451A. Under the cautionary note, the exhaust valve is “identified by the oil drain hole located under the valve end.”
However, the hole that I see is located under the push rod end.
I know I removed the rocker arm with the hole from the exhaust valve, but I do not see how the oil from this hole will lubricate the valve.
This is all probably moot since the engine has been running for 2,200 hours.
A: Mark, you are correct. The explanation regarding how the valve tip gets its oil can be somewhat confusing.
The oil to lubricate the valve tip/rocker arm foot is done by gravity feed and the hole you mentioned allows the oil coming from the pushrod to flow towards the valve tip. This is not a pressure oil area, but simply gravity feed.
As you may know, Lycoming has superceded the 69444 and 74636 rocker arms, which is covered in the Lycoming Service Instruction 1454A rather than SI 1451A that you referred to.
The change in the rocker arms was a result of ease of manufacturing and reducing the overall number of rocker arms in the system.
Producing more common parts that can be used on a variety of engines has been a goal of Lycoming’s in an effort to control and hopefully reduce manufacturing costs, which certainly will help all of us in the long run.