Hi Dennis and group,
Although the P and LX series Onan engines have a pressure lubricating system, not all moving/rotating parts are pressure lubricated. The valve tappets and the rear camshaft bearing are not pressure lubed but splash lubed. What this means is when the oil level is at the full mark and the engine running, oil is splashed up to the valve tappet and rear cam bearing areas. The tappets are designed to rotate as the camshaft lobes push on them to open the valves. The tappets each have a groove cut in them similar to a drill bit and as they rotate they collect a small amount of oil with the idea of being lubricated. The rear camshaft bearing receives the splash oil as it rotates and this is the only way these areas get lubricated. As the engine warms up, these areas will get lubed in time. It takes a while for the oil to get on the tappets and they will make a ticking sound until they get proper lubrication. When an engine is operated with a lower oil level but within the operating range on the dipstick, the splash of oil is not as much as with a full oil operating level. In time if the engine is operated a lower oil levels, the rear camshaft bearing will wear due to lack of lubrication and it will move side to side as it pushes the valves open also making a tapping noise.
Onan has upgraded the rear camshaft bearing so it will collect splash oil more easily. Replacing this bearing requires a major engine teardown however and if torn down, a full inspection of the engine is recommended and repaired as necessary. This brings up another point that Onan parts are becoming increasingly difficult to obtain, so if a teardown is decided, make sure that you have all the parts and gaskets needed beforehand.
Having torn down a few Onan engines that failed, I have found the rear camshaft bearing worn to the point that when removed it was in two pieces.
When doing a valve adjustment always recheck that the settings are repeatable after turning the engine over by hand and if the setting are not repeatable, then the rear camshaft bearing is the suspect.
My recommendations:
Maintain the engine oil level to the full mark using the correct oil viscosity for the season.
Allow both the engine and hydraulic systems to warm up before operating the machine.
Use 89 or higher octane gasoline which will reduce the exhaust temperatures somewhat possibly reducing valve seat failures.
Keep the cylinder cooling fins clean particularly on the side where to oil filter is located.
There is an air seal that slides onto the oil filter, it needs to be there to keep maximum cooling airflow to that cylinder.
Decarb the cylinders at the Onan recommended frequency, very important on these engines.
Mackie

 

We highly recommend doing a decarbon job BEFORE adjusting the valves we have videos and kits for doing both jobs happy to help at caseingersolltractors.com