Reciprocating Assembly
There are some differences in the connecting rods, crankshaft, and pistons used in the Hi-Po 289's assembly. Let's start with the crankshaft. It has been reported time and again that the Hi-Po's crank was nothing more than a cherry-picked stock crank, inspected and deemed "perfect" for use with the higher revving Hi-Po. While this was true for the block casting, the crankshaft was indeed a revised part for Hi-Po use. According to Bob Mannel's excellent book, the Hi-Po cranks were made in batches with higher levels of nickel and magnesium added to stock 289 crankshafts (they did use the stock casting mold as well). This would give the crankshaft increased nodularity, but it was far from an exact science. As such, each Hi-Po crankshaft from these small runs was checked visually. The rear counterweight was polished and then checked with a microscope. If the crankshaft had enough spherical graphite nodules in a specific measured area, it was deemed to have a "high nodular content" and was used for Hi-Po assembly. Ford also added a small "hatchet" shaped counterweight to the front of the crankshaft to move the counter balancing closer to the core of the engine, which necessitated a thinner timing chain.
Most, but not all, Hi-Po 289...
Most, but not all, Hi-Po 289 blocks got the
Ford used this small counterweight...
Ford used this small counterweight slipped over the nose of the crank to move more counterbalancing closer to the core of the engine to reduce crank flexing for the Hi-Po version of the 289. The Hi-Po 289 used a special timing chain set and gears that were narrower than the base 289 to allow room for this counterweight while still clearing the stock timing cover.
The Hi-Po's rods look like...
The Hi-Po's rods look like stock 289 parts until you get to the
The connecting rods and pistons are much simpler. Ford used the standard 289 connecting rod molds to make the Hi-Po rods. As such, you'll see standard C3AE or C3AE-D markings, but where the difference will be found is in the machining, rod cap, and the fasteners. The Hi-Po rod, due to its larger 3/8-inch retaining bolt, had less material removed from the side of the rod during machining. Ford also used a beefier rod cap for the larger rod nut to seat on and to handle the engine's expected 6,000 rpm. The Hi-Po's pistons were specific to the engine, cast from high-strength aluminum for high compression use and with four valve reliefs to accept the high-lift camshaft. While similar to the later A-code 289 piston, which also had four valve reliefs, the Hi-Po's casting number was different. A Hi-Po piston will have a C4OE-A number while the A-code will have a C5OE-H (both with a 6110 base number).
In a close up of the Hi-Po...
In a close up of the Hi-Po cap versus the stock 289 cap (bottom), you can easily see the extra material around the bolt holes to compensate for the larger fasteners.
As noted above, the Hi-Po...
As noted above, the Hi-Po rod came fro, the same casting molds as other 289 rods, and as such will have the standard casting numbers on them--in this case, C3AE-D. It was the machining operation (and aforementioned fasteners and rod cap) that made a Hi-Po rod a Hi-Po rod.
The Hi-Po piston in all of...
The Hi-Po piston in all of its cast aluminum glory (there were no forged pistons in the Hi-Po, contrary to what has been written). The pistons were designed to clear the valves at high lift with valve reliefs in the pistons. Ford had four reliefs cast in so the pistons could be used on either side of the engine during assembly (the notch denotes forward facing when installed in the block).
This is not what you want...
This is not what you want to see when you pull the valve covers off your (supposed) Hi-Po engine. While the bottom end was indeed a Hi-Po, somewhere along the line, the heads were replaced. Notice the press in studs and single spring with no damper inside it--bummer.
There's certainly a lot going on in the Hi-Po's valvetrain area. Starting with a solid-lifter camshaft, Ford also used mechanical lifters (natch), valve springs with fewer coils than standard 289 springs to prevent coil bind at high lift, a flat-wound damper spring inside the valve spring, special hardened retainers, and thicker camshaft thrust plate (before Level 7 engine change) to reduce flexing/distortion of the cam and its higher loading and rpm. Due to the thicker thrust plate, the cam timing gear had to be reduced in thickness to maintain overall dimensions under the timing cover (just like the crank gear mentioned previously). With the thinner crank and cam timing gears, Ford fitted a thinner timing chain to match.
Here's a correct Hi-Po valvetrain....
Here's a correct Hi-Po valvetrain. Note the fewer coils of the main spring, along with the flat-wound damper spring inside. The hardened retainers are thicker than the standard 289 retainers, and of course you can easily spot the screw in rocker arm stud. Finally, the Hi-Po heads use cast-in valve spring seats for high rpm stability, but we'll get to that in our cylinder head section.
This timing chain measured 13/32-inch thick versus the regular 289's 1/2-inch wide chain. Using the wrong combination of gears, chain, and thrust plate will cause wear on the “hatchet” counterweight or even timing cover wear/damage. To confuse things further, Ford used two different cam gears in the timing set. Early Hi-Pos (before Level 7 engine change) used an iron gear; while from March 1965 on, the gear was aluminum with nylon teeth. The iron gear used an additional C-shaped spacer to properly locate the gear on the camshaft, while the aluminum gear has the spacer cast in. In a nutshell, use the iron gear, spacer, and thicker thrust plate together, or use the aluminum gear, no spacer, and standard thrust plate together. Do not mix the combinations.
Our Hi-Po, from a '66 K-code...
Our Hi-Po, from a '66 K-code fastback, used the later aluminum gear with nylon teeth, which was in surprisingly good shape (we've seen the teeth completely worn away, creating a no-start condition). Notice too that the Hi-Po uses an oil slinger on the crank.
Here's a close up of the narrower...
Here's a close up of the narrower Hi-Po chain. Using the standard 1/2-inch wide chain will bring nothing but trouble (and metal shavings) to your Hi-Po build, so make sure you have the proper combination of timing parts for your build.
This Hi-Po flat-tappet mechanical...
This Hi-Po flat-tappet mechanical cam has seen better days. Thankfully, the cam is still available from a few sources. While we're big believers in converting to roller cams for their power and lack of Zinc requirements, the cam (and lifters) is what makes the distinctive clack-clack-clack sound of the K-code engine and we certainly don't want to lose that with our rebuild.