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Ron..... ....N-Engines are designed to be rebuilt many times because of the "life" they lead. Dirty, dusty, hard pulling, constant rpm governed, heavy loads. So instead of "re-boreing" the engine block once (like regular auto engines) to correct for cylinder wear, you replace the worn sleeves as many times as you need to. Ford originally used a thin steel sleeve and later in the 8N's "improved" to a thicker castiron sleeve for better wear characteristics. Pistons are still the same diameter. You can "bore" out a thin sleeve block to take these castiron sleeves. This ia a good thing. Ford originally used a 4-ring piston, 2 compression and 2 oil control rings. Improvements in oil ring design and to reduce internal friction, they changed to the more common 3-ring piston design. If'n yer replacing pistons, go with the 3-ring. This is a good thing. The original N-Valves were "non-adjustable" and if you "ground the valves" (valve heads or valve seats) to cbtain correct valve stem clearance, you had to physically remove the valve from the block and grind the end of the valve stem for more clearance. And there is always the possiblility of overgrinding and having too much clearance. So some genus developed the adjustable tappet. This is a good thing. Then someone looked at the exhaust valve wear and discovered if they made a "little ramp" on the tappet seat, the valve would rotate a little bit and keep from burning a spot and make the valve seat last longer. This is a good thing. But you don't have to use the improved stuff, if'n you don't want to. Its your dollar..... ...Dell
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