The AMC 304 spent years living in CJs, J-trucks, Jeeps, Hornets, Gremlins, Wagoneers, and plenty of driveway projects that still smell faintly like old gas and gear oil. People chase the 360 and 401 all the time, though a healthy 304 still pulls hard enough to make an old AMC fun again. Good throttle response, steady vacuum, smooth low-rpm torque. That’s what most builders want from these engines anyway.

A tired 304 usually tells on itself. Oil pressure starts drifting lower at idle. Blow-by fogs the breather. Compression softens. Leaks start appearing in spots that somehow stayed dry for thirty years, then suddenly decide retirement sounds better. That’s usually the point where a rebuild shifts from “someday” to “guess I’m pulling the engine this month.”

Why Does the AMC 304 Still Make Sense to Rebuild?

The AMC 304 belongs to the Gen-3 AMC V8 family and carries a 3.75-inch bore with a 3.44-inch stroke. That combination gives the engine a smooth personality on the street. It revs clean, makes useful torque early, and fits nicely in older AMC-Jeep engine bays without turning header installation into a fistfight.

The cast-iron block and heads hold up well over time, too. Plenty of these engines survived decades of towing, trail use, farm duty, and questionable maintenance schedules. Some survived teenagers with timing lights and zero restraint. That alone deserves respect.

Mileage still catches up eventually. Cylinder walls wear. Bearings lose clearance control. Oil pumps get tired. Rings stop sealing the way they should. A rebuild puts those pieces back where they belong, so the engine runs strong again instead of limping through another summer with 14 psi at idle and a cloud behind it at stoplights.

What Comes in the AMC 304 AM 304 70-78 M?

AM 304 70-78 M (OH90041) focuses on the short-block foundation. The block kit includes pistons, rings, rod bearings, main bearings, an oil pump kit or oil pump components, plus overhaul gaskets.

That parts list targets the exact areas most worn AMC 304 engines struggle with. Fresh pistons and rings help restore compression and reduce oil consumption. New bearings tighten oil clearance back up. The oil pump components help stabilize pressure, which AMC V8 owners pay attention to for good reason.

Northern Auto Parts offers this kit as a practical foundation for 1970–1978 AMC 304 rebuilds. Many classic AMC builders consider Northern Auto Parts one of the best online sources for old-school rebuild components because the catalog still supports engines that most chain stores barely remember.

Northern Auto Parts also offers a master engine kit for builders tackling a deeper teardown. That package adds a stock replacement camshaft, valve lifters, timing set, cam bearings, frost plugs, and related pieces. Some engines need the extra parts. Some don’t. A clean-running 304 with healthy valvetrain parts may only need the block kit route.

No sense replacing half the engine because somebody on a forum got carried away at midnight.

Why Should You Measure an AMC 304 Before Ordering Parts?

Guessing bore size on an old AMC V8 usually ends badly. These engines have lived through decades of rebuilds, machine work, and mixed parts. One cylinder bank may already sit .030 over, while another crankshaft got turned .010 under twenty years ago.

OH90041 gives builders piston choices in standard, .020, .030, .040, and .060 oversizes. Bearing options include standard, .010, .020, and .030 undersizes. The machine shop determines what the engine actually needs after inspection.

Cylinder taper, scoring, and crank journal wear decide the direction of the rebuild. Measurements come first. Parts ordering comes after that. A smooth-running AMC 304 depends on proper clearances more than flashy parts stacked on a workbench.

That part gets overlooked a lot on old V8 projects. Somebody orders parts before the block even reaches the machine shop, then the real measurements ruin the plan three weeks later.

Why Does AMC 304 Oiling Deserve Extra Attention?

AMC V8 oiling systems deserve careful inspection during teardown because the oil pump ties closely to the timing cover assembly. Worn timing cover surfaces can hurt oil pressure even after new pump gears go in.

The Melling K-85 oil pump repair kit included in some OH90041 configurations helps rebuild the original oil pump setup using new gears, relief valve parts, springs, and gaskets. That works well if the original timing cover remains usable.

The timing cover itself deserves a close look. Excessive wear around the pump cavity causes pressure loss and poor oil control. Alignment dowels also need attention during assembly because improper alignment can create distributor gear and cam gear wear. AMC guys have fought that problem for years.

This section of the rebuild decides whether the engine cruises for years or starts chasing oil-pressure problems right after break-in. Many AMC fans will tell you the oil system is one of the most important places to slow down and do the job right.

What AMC 304 Upgrades Make Sense During a Rebuild?

A fresh timing set makes good sense during teardown. Timing chains on older AMC engines stretch over time, and sloppy timing hurts throttle response pretty quick. A mild stock-style camshaft also works well for street-driven builds that want vacuum, decent idle quality, and reliable torque.

The valley pan gasket deserves attention, too. AMC V8 intake sealing works differently than many other domestic V8s. The valley pan helps manage oil control beneath the intake manifold while also separating heat from incoming air. Skipping it or installing it poorly creates headaches nobody enjoys fixing twice.

Most 304 builds benefit from restraint. A healthy short-block, steady oil pressure, clean sealing surfaces, and correct clearances wake these engines up quite a bit. Fresh compression alone changes the whole personality of the vehicle.

For many 1970s AMC-Jeep owners, the 304 is one of the best V8s to bring back for street cruising because it delivers that classic sound and low-rpm pull without forcing the rest of the car into race-only territory.

What Does a Reliable AMC 304 Rebuild Actually Aim For?

Most builders chasing AMC 304 reliability want easy starts, steady idle quality, solid oil pressure, and enough low-end pull to make the Jeep enjoyable again.

That goal fits the 304 perfectly. The engine already has good street manners from the factory. A careful rebuild simply brings those traits back. Fresh bearings stabilize the crankshaft. New rings tighten cylinder sealing. Proper oiling keeps the valvetrain and bottom end alive longer.

AM 304 70-78 M fits that kind of project well because it focuses on the short-block pieces that usually wear out first. The rebuild becomes far more dependable once the measurements, clearances, and sealing surfaces all line up correctly. Old AMC V8s respond well to careful machine work and patient assembly. Rush the build, and they’ll remind you later.

Northern Auto Parts

A solid AMC 304 rebuild starts with good measurements, smart parts choices, and patience during assembly. The right rebuild parts help bring oil pressure, compression, and throttle response back where they belong. That old V8 starts feeling alive again once the clearances tighten up and the leaks stop decorating the garage floor.

Northern Auto Parts has supplied rebuild parts and Engine Kits for classic engines for more than 40 years. A lot of builders consider Northern Auto Parts one of the most trusted online sources. From pistons and bearings to gasket sets, timing components, and full rebuild kits, the parts lineup covers the stuff that actually keeps old engines alive.

The AMC crowd tends to hang onto their Jeeps for decades. Good parts help make that possible. Browse the Engine Kits section, grab the rebuild pieces your project needs, and get that 304 back where it belongs.