Modifying AMC oiling for performance

By: MSD | 10/02/2015 < Back to Motor Life Home

An age old hot rodding adage goes something like: “An engine is more than the sum of its parts”. While that oft-repeated saying has been tossed around so much as to be threadbare, that doesn’t make it any less true. Details are key, and are what separate two otherwise identical engines. Many enthusiasts are so focused on choosing parts that they sometimes overlook little things in assembly that will improve their engine’s durability as well as its performance.

One example is careful preparation of the oiling system. They may believe the factory knew what it was doing when it designed the engine, so they see no need to mess with it. What they fail to take into account is manufacturing tolerances and things like core shift during the casting process. They also may be overlooking the fact that they are asking far more of their engine than the manufacturer had intended it to provide.

American Motors enthusiasts know that their marquee’s V8 engines have a unique oiling system that requires special consideration. These engines supply oil to the distributor gear last and via a circuitous path, which needs careful preparation to ensure adequate oil flow. There are several key areas to focus your attention, and we will highlight each of them in this story. This discussion applies to AMC’s from 1967 and on: 290, 304, 343, 360, 390, and 401 cubic inch varieties.

Follow along as we outline the trouble spots in the AMC V8’s distributor lubrication scheme and show you how to counteract them. A little extra attention given to the oiling system with these simple modifications during your next build will pay big dividends down the road.

  1. When performing final engine assembly, the first critical point is the front camshaft bearing orientation. Placement of this bearing requires precise alignment of the bearings’ oil feed hole with the block’s oil gallery. This ensures maximum oil flow to the camshaft’s front journal groove. The groove must completely encircle the journal in order to ensure proper lubrication throughout the camshaft rotation.
  2. There is a single bore in the front camshaft bearing journal groove that exits on the front face of the journal. This in turn feeds a groove in the rear of the cam timing sprocket. Be sure that the cam bearing or bearing journal (or both) is grooved. This is absolutely critical to proper camshaft and timing gear lubrication.
  3. Looking at the back side of the cam timing sprocket, make sure this groove lines up with the hole in the front of the camshaft. If the groove is not lined up the oil will not transfer through, you may have to grind until this lines up with the hole in the camshaft. The oil moves down the groove to a chamfer at the center bore then to a passage adjacent to the keyway. This passage is typically quite rough and benefits greatly from some clean up with a small file to minimize oil flow restriction.
  4. On the front of the cam timing sprocket is another chamfer, along with six small grooves on the face of this surface. These grooves redirect a small amount of oil to the timing chain and the fuel pump eccentric.
  5. From the timing sprocket, the oil continues on through the passage in the fuel pump eccentric adjacent to the keyway, and then to the distributor drive gear.
  6. The distributor drive gear has four holes amongst the gear teeth where pressurized oil is fed to the distributor gear.
  7. When this gear is installed, it is critical that these holes are not obstructed by the camshaft snout. The camshaft to the end of the gear has an open area so oil can feed through these holes.
  8. The camshaft retaining bolt and washer serve a dual purpose. Their installed height is important as they constitute the camshaft thrust button.
  9. Additionally, the diameter of the washer is critical as it seals the end of the distributor drive gear; forcing lubricant through the distributor drive gear’s oiling holes.
  10. There are some aftermarket front covers in circulation that also contribute to distributor gear failure. Before final assembly of the engine, test fit the distributor, oil pump gear and cover. With the distributor completely seated without the gasket in the oil pump shaft, and the pump gear fully seated in its housing, check to see if the distributor flange is seated against the top of the cover or if a gap exists, as shown.
  11. The distributor should bottom out in the front cover with no gasket when the oil pump is installed, if distributor does not bottom on the cover there could be a timing cover problem or the oil pump shaft groove depth issue. It could be the radius on the bottom of the oil pump groove to large, in which you can clean this with a file to get the proper fit.
  12. When installing the timing cover during final assembly, do not overlook installation of the dowel pins in the block. These will insure proper cover alignment.
  13. After installing the cover to the engine, install and test fit the distributor. Note, when installing the distributor, it should slide easily into place. If not, there may be an alignment issue, one of the Timing cover manufactures had issues with alignment of this cover and depth of the oil pump and distributor, this would cause the distributor to bind as it was installed and cause gear failure.
  14. At this point of the engine assembly, you should verify the distributor gear will be sufficiently lubricated. This can be observed through the fuel pump mounting hole. Using an oil pump priming tool, look for oil streaming around the outside of the distributor drive gear. Additionally, you should rotate the crankshaft and be sure this oil stream continues for two revolutions of the crank.
  15. When these procedures are completed install the distributor
  16. Note, the use of racing oil will help the gears break in. This type oil has zinc which the oil manufactures removed from standard automotive oils. The zinc will help the gears mate.