I finished some machining on my current 390 stoker A-block build and wrote up a tech article on oil system modifications for A block engines (277, 301, 303, 313, 318, and 326) that might interest some people. Many of the techniques are also applicable to early Hemis and hemi-block polys. These modifications are beneficial for both stock and performance builds. The writeup along with many other tech articles are available at https://poly318.com/oil-system-modifications.html

Poly A-block Oil System Modifications

There are some easy modifications that will improve the A-block oiling system over the factory’s design and finish work. The easier oil flows through the system at maximum volume and the quicker oil gets to necessary components and back to the pan the better. Ensuring the timing set gets good lubrications is also beneficial. 

The oil pump, rear main cap, and block rely on drilled oil galleries, a series of drain-back holes cast into the lifter valley, and two drain-back holes drilled into the front of the block that lubricate the timing set. The issues are that the drilled gallery holes have ridges and 90° turns with sharp edges; the cast drain-back holes have rough flash that impedes oil flow; the front drilled drain-back holes are placed too high above the valley floor where oil is more likely to drain through the valley holes first; and the factory spin-on filter adapter uses only four 1/4" holes that limit volume and create turbulence in the chamber.

To address the casting issues, use a die grinder and tapered and ball long-reach carbide bits to rework the areas. For the filter adapter, use a center punch and 1/4" drill bit.

1. With the oil pump disassembled, use the ball bit to smooth out the outlet in the gear chamber (Figure 1). Caution: be careful not to damage the floor and wall where the gears ride. Note: the figure is using an old pump for demonstrative purposes. For new pumps, block the regulator piston chamber with masking tape to protect it from the shavings.
2. Using the ball bit, smooth out the ridge on the oil pump outlet (Figure 2).
3. Using the tapered bit, smooth out the ridge on the rear main cap inlet (Figure 3).
4. Using the ball bit without spinning it, reach down the rear main cap passage and feel the walls for any offset between the cap and the block connection. Remove any offset moving the bit up and down (Figure 4).
5. After removing the rear main cap, reach the ball bit down the filter intake passage where the horizontal gallery intersects and round off the long-turn ridge. Catch and round off the sharp short turn with the back of the ball (Figure 5). Note: 1956 – approx. 1962 blocks may have a bypass valve instead of a blind hole or plug. If using a canister filter, this valve should be tested and replaced if necessary since they often deteriorate. If using a spin-on filter, the bypass valve needs to be removed and the passage plugged (see my oil bypass valve technical article for plugging information).
6. Using the ball bit, chamfer the oil filter chamber intake hole and smooth out the chamber of all rough casting and ridges. In particular, the outlet gallery plug has a sharp cliff directly in the line of flow where the oil enters the chamber (Figure 6). Caution: be careful not to grind the adapter plate sealing surface or threads.
7. Using the ball bit, reach into the filter outlet and round the sharp long turn. Catch and round off the sharp short turn with the back of the ball (Figure 7). Caution: be careful to not damage the threads.
8. Using the ball bit, reach into the plugged outlet gallery through the filter chamber and through the back of the block and round the sharp short turn (Figure 8). Caution: be careful to not damage the threads.
9. Using the tapered bit, remove flash from and chamfer the oil drain-back holes in the lifter valley (Figure 9).
10. Using the tapered bit, remove the vertical flash toward the rear of the valley that impedes flow (Figure 10).
11. Using the tapered bit, elongate and radius the front drain-back holes (Figures 11 and 12). Caution: be careful not to thin out the cam retainer thread bosses too much.
12. Using the ball bit, chamfer the four oil drain-back holes in the cylinder heads (Figure 13).
13. Drill and chamfer an additional eight 1/4" holes in the oil filter adapter plate (Figures 14).

Figure 1: Poly A-block LA Oil Pump Outlet Smoothed

Figure 2: Poly A-block LA Oil Pump Outlet Smoothed

Figure 3: Poly A-block Rear Main Cap Oil Passage

Figure 4: Poly A-block Rear Main Cap to Block Connection

Figure 5: Poly A-block Block Rear Main Oil Intake (blocks without a bypass valve)

Figure 6: Poly A-block Oil Filter Chamber

Figure 7: Poly A-block Oil Filter Outlet

Figure 8: Poly A-block Oil Filter Outlet Smoothed

Figure 9: Poly A-block Lifter Valley Oil Drain Holes

Figure 10: Poly A-block Lifter Valley Flash Removed

Figure 11: Poly A-block Front Oil Holes

Figure 12: Poly A-block Front Oil Holes

Figure 13: Poly A-block Cylinder Head Oil Drain Holes

Yes, all A-blocks will accept hydraulic lifters. Not only did the one-off 326 have hydraulic lifters, but many heavy-duty trucks, industrial, and marine A-blocks had hydraulics. The downside of the factory hydraulic engines was that they used non-adjustable rocker arms, but the solid-lifter adjustable rocker arms swap in.

Lifters:

• Solid: TRW VL31
• Hydraulic: Melling JB879

Pushrods:

Solid Lifter: Sealed Power RP3030 (5/16” x 8.418”)

Hydraulic Lifter: MPR153 (5/16” x 8.364”)

As for cams, Schneider, Racer Brown, and Camcraft have hydraulic grinds.

I'm not sure why the oil pump photos broke, but here they are. This process uses a standard-volume M-72 pump but replacing the OEM spring with a high-pressure spring.

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(Pump_Outlet3.jpg)

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Pump_Inlet3.jpg (164KB - 146 downloads)

Pump_Outlet3.jpg (198KB - 134 downloads)

Pump_Cover2.jpg (216KB - 131 downloads)

Pump_Outlet2.jpg (192KB - 135 downloads)

Pump_Plug2.jpg (172KB - 130 downloads)