Tractor Repair: Ford 4000 Diesel, oversized pistons, oversize pistons

Question
I had my tractor repaired it was blowing oil through the exhaust. They honed the cylinders, replaced the rings (2 were broken) and bearings.I have used it twice and it is still blowing oil!! They took it back to the shop and put it on the Dyno; pushed it hard with no problems except that it was blowing some oil at idle. They told me that the rings have to seat themselves on the cylinder walls and after 50 to 100 hours the motor should not use oil!
My question is are they giving me a line of BS or is this really true.I think they should have rebored the cylinders and installed oversized pistons.

Answer
Hello,

  Sometimes an engine does have to run for 100 hours or so to seat the new parts, that's why a new machine will have the break in instructions saying not to put it under full load, and not to run it at a continuous speed for very long.  Once the parts have worn against each other and gotten broke in, then it's OK.  It would be a waste of time and money to rebore the cylinders and install oversize pistons if the cylinders were still within the wear limits.  The shop that did the repair must have measured them with a bore gauge and determined that they were OK.  If there were 2 broken rings, then this wasn't all done for nothing, they did actually find something wrong that needed to be fixed anyway.  Does the engine oil level drop and do you have to keep adding oil?  With a diesel engine, sometimes it looks like oil coming out the exhaust, but it's actually unburned fuel from incomplete combustion.  This can be from low compression, bad injectors, incorrect timing, bad injection pump, or an engine that's not running up to correct operating temperature.  It can look just like black oil, but it is usually unburned fuel.  The valves should have been checked while the head was off to do the rings.  I would recommend doing a compression test and checking the timing, and if that is satisfactory, then have the injectors tested or rebuilt.  If that still doesn't cure it, then the last resort should be the injection pump.

                              Arnie