Y2KGUII ZD Wgn
A rule of thumb is 0.001" play per inch of bore and bearing diameter, give or take a little depending on how it will be driven.Now onto the not so great news. It might've seemed above that I can just buy all new genuine gaskets for the engine, give it a good clean inside, put it all back together, and have a recently rebuilt engine all well and good, but that's probably not the case.
While the top end has clearly been rebuilt, Dad's suspecting that the bottom end hasn't been touched, or has been touched but put back together the way it was.
Basically, there's a lot of play in the pistons inside the bore, and the thing that worries him most is that there's a small amount of rotational play as well; as in, you can rotate the pistons slightly either way.
The other thing too is that it looks like the bores have been honed, but probably not much, as you can still see the honing marks all around the cylinder. Problem is you can also see some pretty significant scratch marks up the sides of each cylinder too, perpendicular to the crank and gudgeon pins. So it seems that the bottom end bearings, and/or the gudgeon pins, have some play in them. It also seems like after the bore was honed they either didn't replace the rings, or replaced them with standard size, not oversized ones to suit the hone, which could be contributing to the piston play.
If you rock the pistons side-to-side in the cylinders they knock against each side of the wall as well, not sure if this is normal but dad suspects this is where my engine had a noisier, knockier, and generally slightly rougher idle than the farm ute we've got.
Pics of the cylinder bores, and a video of the piston movement, to come.