When to run an overhead?

that is not quite true. I changed my oil on a 96 N-14 every 25000-30000 miles, no bypass filter, and took the thing to 1.4 million miles and never opened it up except for overhead and replace one injector. Still only used a gallon of oil every 8000-10000 miles and got 7 mpg. Oil samples were still within limits. Doing the same with my '06 ISX with 718,000 miles on it and the oil samples are as good or better than engines with half that life. Oil samples are the best insurance to let you know what is really going on inside without having to turn a bolt.

Each engine is different. Only an oil sample will let someone know how long they should go before changing the oil. Most every manufacturer has at least a 25000 mile interval or more. Same for auto engines. The days of 3000 mile oil changes in them is over except for those that have a perception that it will make a difference.

Sure, oil changes are cheap compared to a rebuild, but there is really no need to throw away good oil before its time. But old habits die hard.

 

I was involved with a customers test of a synthetic oil, we added spinners, a great thing to add to any engine, and a oil pressure tap so an oil sample could be removed easily, after about 5 to 6 hundred thousand kilometers, and two bearing rollins, compared to an exact copy fleet using dyno oil the synthetics experiment was a failure. the engines were extremely dirty inside, and the bearings showed a lot more wear and impregnated foreign material. By the time the oil tests were included and the cost of the oil it was not cheaper.
The oil in a modern engine is not only the lubricant but the major coolant as well, You can run the oil a lot longer than was possible before, Because the oil is better and the filters are a lot better, use of a spinner, properly installed and maintained is a great addition.
As the engine wears the oil will break down quicker, after an oil change the oil usage is near "0" when the usage starts that is the 1/2 life of the oil, if it starts using oil before 1/2 the mileage of your regular scheduled oil changes then you should shorten the mileage to oil changes.
You also want to look at the bearings, what are they looking like, the lowering of sulfur in the fuel has been a bonus for oil life.
Just a thought!

 

what is overhead. what you guys mean by that?

 

Adjustment on the valves and injectors

 

I've always called it a "valve set"

 

Lol , then you get the real old timers who call it "running the rack". That' term is from back in the 2 stroke Detroit days.

 

I am old school. Put your ear close to valve covers. If you hear something clicking louder than the rest pull the valve cover and check the valves. Too tight and you can burn a valve-too loose and its not opening far enough. A stethoscope should be in every mechanics tool box. Over time and milege valves sink into head and the valve clearance changes. I do my race car 2-3 times a summer.