Failed 210 overhaul revisited…..again

Thought and discussions?

A couple of thoughts as this issue keeps going on: #1. Their 210 engine had an original piston that was scored. WHY was it scored ?? Why aren't we concerned about it??   #2. The only 426 engines I've really ever had a piston scoring issue with (for the sake of scoring pistons) is any of the non-piston cooled engines (D21-210-220 and 7030). The same piston/sleeve combo is used in piston cooled engines and hasn't ever really been an issue for me. What would that tell you??  Oil cooled pistons run cooler and don't swell up as much as non-piston cooled pistons.  #3. I know a lot of time and effort was put into warming and cooling pistons and measuring skirt diameters and comparisons of new aluminum to old aluminum. I don't believe it is still quite the same as a piston in actual operation, because under full load/HP output the piston top temperatures are over 1,000 degrees F. I'm not saying the skirts are 1,000 degrees, but I am saying things could be hotter than tested and again a piston cooled engine will be COOLER because of the oil spray bath designed to take away that heat.  #4. Lastly. I can't say I've ever overhauled a single one of these engines that were "worn out" from excessive piston to sleeve clearance. The overhaul was due to scored pistons/sleeves or too much ether used, broken #2 rings or a dusted engine which usually failed the rings or ring lands. So, all the focus on having too much skirt clearance being a terrible thing isn't really worth talking about. Of course, this is just my opinion from decades of fixing these engines. At this point, I really don't care what anyone does. You just live with the results however they turn out. 100 hrs of run time isn't a big test. 1000 hrs at 100% full load and an occasional loose set of fan belts or a dirty radiator that takes the coolant temps to the red line a time or two would be more of a test, don't ya think ?? Because that's what really happens in the real world of farm tractor engines.     EDIT:  I doubt that the old pistons had an "oval" piston pin bore due to their age. Later on when the 7080 engine came out, A-C went to a piston pin bore that was bigger side-to-side than it was top to bottom. This allowed for piston pin flexing without putting undue stress on the piston body itself. Wonder if the new piston has this feature??  it should have because it was a running change/improvement to the piston design. Don't remember for sure but I think it was .0005" to .0010" wider than top to bottom dimension.

Edited by DrAllis - 16 Jul 2023 at 6:39pm

and, Dr. , one always see's "the tractor is set a XXX HP" which is usually way over 10% above the OEM setting.  There is a reason an engine is set at a specific HP - go over that and sometimes it works, sometimes not.  The Harvey plant set the new engines at 10 % over rated hp and ran at 100% load.  They determined wear would rack up at a factor of about a 1/3 more than the average 80% load a tractor usually runs at - thus saving time on the dyno to determine if the engine meets engine life requirements.

I'm a jack leg but just a thought were the sleeves in spec to begin with?