Good questions!
I don't think that I have ever seen much of a "ridge" at the top of the cylinders on these Mazda engines. Definitely pull the cylinder head and look for a ridge at the top of any of the cylinders first.......don't be fooled by carbon build up there. Spray some Brake Cleaner on a cloth towel and rub the carbon off the cylinder walls and see what you have there.
If not much of a ridge, and you can still see honing cross hatching, it is a good candidate for a "JY rebuild"!
You will want to measure the cylinder diameter to determine if it is still a standard bore or not. Sometimes the pistons will have etched numbers on the top to indicate an overbore size. I have a Dial Bore Gauge now, but before that I used Snap Gauges and a larger Micrometer........and it is pretty accurate using them......just take your time getting the Snap Gauge set to the bore diameter.
And YES! I have rebuilt these engines with as many miles as yours, WITHOUT any machine work being done, and I reused the stock pistons. I have one in my Red Regular Cab truck and have put another 100K miles on it since I rebuilt it in 2011. I think that engine only had 180K on it when I rebuilt it though.
Bottom line, if there is not hardly any ridge at the top of the cylinders, and minimal or light, vertical scoring/scuffing in the cylinders.....I would not hesitate to rebuild one without boring it and buying new pistons for it.
Take some pics of it Mitch and post them in the thread for your build, and I will follow along and offer any suggestions!
