engine hours, whats a lot?

If the engine is well cared for and maintained, conceivably it could go twice that time period. It basically boils down to use and abuse plus lack of maintainance to determine how long it will last on the original build. A lot of the bigger industrial engines I work on, some manufacturers claim 20,000 hours before servicing heads, with an overall evailuation of the bottom end. Others manufacturers recommend a total rebuild at 20,000 hours.

With the old range of machines built before 1958 you run them until they burn too much oil or the oil pressure starts to drop, if you have to remove a head for valve work, take a look at the bores then, in recnt years I have been involved with Cat engines which have done over 52,000 hours on the original liners, rings and bottom end bearings.

I work for an oilfield drilling company's engine shop. We just did a rebuild on a Cat 3512B genset engine with 66,000 hours. Cat gave us some new parts just to get the old parts since the hours the engine made on original parts.