10/26/2026
I repost this AMC Oiling system hints and tip guide from time to time to provide an oiling system hints and tips for followers of this page. It has helped many AMC a Jeep owners avoid pitfalls of unknowingly using defective parts on their AMC V8 engines and to build a bulletproof oiling system. It is also listed as a downloadable file at the top of the AMC Questions and Answers Group.
The only real issue in the oiling system was that some blocks did not have the rear main bearing oiling journal drilled all the way through which caused starvation to the rear mains and rods. But that is easy enough to check by turning the block upside down on an engine stand and shining a light through the rear plug opening for the camshaft and looking up into the rear main journal to see if it is the same diameter all the way through. And it is always a good idea to smooth and enlarge the factory drain holes in the heads and block and well as debur and smooth sharp edges in all oil journals in the block and front cover. Some folks put chain oilers in the front cover or drill a small .040 hole in the plug behind the timing chain so it will sq**rt oil on the chain but if you do that be sure to put some drainage reliefs on the bottom inside of the timing cover.
Also, AMC engines were actually designed to have five quarts of oil in the pan PLUS one in the filter but AMC did not want to be the only manufacturer to require 6 quarts of oil so marketing forced them to say it only needed 4 in the pan plus 1 in the filter so that AMC oil changes would not cost more than their competitors. Nearly all the other issues are parts or builder related such as follows:
• After market timing sets made incorrectly where the oil groove on the back of the timing set's cam sprocket is too tall allowing oil to sq**rt out rather than go to the cam and distributor gear.
• the timing set's cam sprocket oil chamfer stops in the wrong location and prevents enough oil to pass to the cam and distributor gears
• after market cam and distributor gears are made incorrectly with the oil hole in the cam gear too far rearward cutting off oil flow to the distributor gear
• after market cams having too small of a hole on the front of the camshaft resulting in low oil volume going to the cam and distributor gears
• after market timing covers made incorrectly with the distributor hole drilled on an incorrect angle causing the oil pump shaft to bind on the bottom of the distributor when rotating
• after market timing covers made incorrectly with the flat surface at the end of oil pump cavity milled on an angle causing a variation in the pump gear clearances
• flashing around oil journals in aftermarket front covers
• flashing around the oil journals on aftermarket pump cover/oil filter adapters
• incorrectly drilled pressure relief plunger holes on aftermarket pump cover/oil filter adapters preventing the pressure relief plunger from seating all the way which allows oil pressure bleed off or jamming and blowing out the filter
• after market pump gear kit gaskets being .0105 - .011 instead of the correct .0075 causing cavitation under the oil pump gears • oil pump/oil filter adapter covers being convex or concave causing variation in pump gear end clearances
• rod bearings lacking the little notch that allows oil to sq**rt up on the wrist pins
• rod bearings having too thin shells resulting in excess rod bearing clearances of .003 or more on .010, .020 or .030 ground cranks
• excess resizing of rods closing off the little notch in the rod caps that is also there for lubricating the wrist pins
• oil restrictor disc lacking in aftermarket anti pump lifters
• oil restrictor discs being installed upside down during lifter assembly resulting in excess oil pumped up through the pushrod and flooding the cylinder heads
• after market lifters being too small for our lifter bores. Lifters used in AMC engines should be no less than .90374. We have seen some name brand lifters come in at under .903.
• after market oil pan pickups having the screen tucked up tight against the internal pickup tube. The screens are not flat and they are sometimes assembled in the pickups with the screen oriented to be concave instead of convex.
• bottom of factory oil pans slightly pushed in resulting in too little clearance between the pickup and the bottom of the pan. The button on the bottom of the pickup helps but the head of the pickup can get bent to one side resulting in the amount of oil it can such up from the bottom of the pan to be greatly reduced
• and one of the most common issues we have found is how AMC crankshafts are ground. AMC bearing clearances require an extra .001 clearance on the rear main. We see an alarmingly high number or crankshafts with the same journal size front to back as well as really poor chamfer on the edges of the rod and main journals on lots of crankshafts we pull out of previously rebuilt engines
• incorrect bearing clearances and piston clearances on a rebuilt engine. These are not SBCs, Fords or Mopar engines rather they are AMC engines yet WAY too many engine shops treat our engines just like any other engine which results in premature engine failure that people are all too eager to blame the oiling system. The reality is that the engine failure was the fault of the engine builder not paying close enough attention to the AMC engine build specifications and/or using incorrectly made replacement parts.
Any one of the above issues can impact the performance of the oiling system and a combination of just a couple of them will often cause an engine failure. The AMC V8 oiling systems is nearly identical to the Buick V8 oiling system yet you rarely if ever hear about their oiling system problems. Why? Because they are usually built correctly and within factory specs and tolerances. Sadly, AMC engines are frequently rebuilt incorrectly by being outside of factory specs and tolerances and yet the engines are blamed for the failure rather than the incompetent builders. If you blueprint an AMC engine build and use forged pistons with a balanced rotating assembly it is
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