These hollow rockers sometimes caused oil pressure loss when their end plugs came out.
Fall 1947 The new “61” and “74” engines are announced for 1948, to replace the Knucklehead.
The 61’s bore and stroke are 3.3125 x 3.5 inches = 60.3 cu.-in., and the 74’s was 3.4375 x 3.96875 in. OHV had overcome much of the 74- and 80-inch flatheads’ overheating problem. To give the new engine the ability to handle the heat of higher-power operation, head cooling was greatly boosted by switching material from cast-iron to aluminum, with three times iron’s heat conductivity.
Because even high-strength aluminum is too soft to act as a valve seating, valves were seated on shrunk-in hard seat rings.
Because of the higher heat expansion of the aluminum heads, it was decided to incorporate hydraulic clearance adjusters into the tops of the four pushrods.
Steadily improved through 1953, with millions produced, the flathead achieved acceptable reliability.
Ford solved most of the flatheads ills over time, upgrading ignition, redesigning water pumps, refining carburetion and boosting displacementto 239 cid and on to 255 cid in the 49-53 Mercury.To achieve that goal, foundrymen at the giant Rouge plant had to work with some 54 cores for each new block.They had to be precisely fitted into molds before the molten iron could be poured, and 3,000 blocks per day could roll off the lines.Engines that have nearly the same bore and stroke (a 1:1 ratio or so) are referred to as "square." Engines with a bore appreciably larger than the stroke are referred to as "oversquare," and the opposite, with a stroke larger than the bore, is "undersquare." An undersquare engine tends to be tall.The longer the stroke, the taller the engine is to make room at the top for the travel of the piston and at the bottom for the throw of the crank.The sidevalve's poppet valves are usually sited on one side of the cylinder(s).