392 Rebuild

Oct. 01, 2005 By Willie Worthy

Reproduced from 4X4 Answer book

International: Anything less is just a car. That's what International wanted us to believe when they were still building Scouts, Travelalls, and pickups. International Harvester products had a kind of down-to-earth design, probably due to their farm-implement heritage. In fact, almost every IH vehicle was referred to as a "cornbinder." IH's V-8 engines are noted for their dependability and longevity, but not as high-performance engines. You just don't walk into your local speed emporium and order a high-rise aluminum manifold for an IH engine. There are four versions of the V-8, all sharing the basic configuration but not complete interchangeability. They are designated 286, 304, 345, and 392 by their cubic inches of displacement. They can be identified by the first three digits of the serial number stamped into a raised boss near the fuel pump. Since there is no substitute for cubic inches, the 345, and the harder to find 392, should be your choice. The two crankshafts are interchangeable and, as far as I know, identical. The 392 makes up for its bigger size in the cylinder bore diameter. The heads are also interchangeable, with the port size being nearly the same. However, the 392 has larger, sodium-filled valves. Exhausts are 1.734 versus 1.609, with intakes of 2.078 versus 1.979. These sizes are adequate for the engine's limited-rpm capability. The exhaust ports themselves are quite restricted, so if you're planning an "all-out engine," some quality porting work will be necessary. Pay particular attention to the cylinder head years; starting with No. 1013196 there was a change In the cooling design. A different head gasket is necessary -- the water leaks told me so.

IH had, from what I've found, three oil-pan configurations. Two were front-sump designs, and the other was a much more desirable rear sump. The pickup tube and oil pump must match the pan. I've only seen rear sumps on full-size late Travelalls. A variety of rocker arms are available, depending on the year and engine size. I prefer the "boat" design, similar to those of Ford and Chevy. Be sure to use matching pushrods. The only intake manifolds available are those from the factory. The 266 and 304 are limited to a two-barrel design, while the 345 and 392 had the factory option of two styles of four-barrel models-a dual-plane spread bore with a Carter Thermo-Quad and a square bore that used a Holley.

Now that some of the background information is out of the way, let's get into the building of a high-performance engine that will still retain that IH dependability along with improved performance and fuel mileage. Our IH truck started out with a 345cid engine, and in stock form produced 94 horsepower at 3,600 rpm to the rear wheels on a chassis dyno. Our new modified 392 doubled that figure with 200 horsepower at 4,200 rpm. It will rev cleanly to 5,000 rpm-plus, but likes no more than 3,400 rpm for constant usage, such as on a long hill with our fifth-wheel trailer in tow for a total load of nearly 19,000 pounds. We did absolutely nothing trick to this engine. We could have matched intake manifold port configurations, ported the heads, or any of the other modifications, but our idea was to put together an engine using basic machining practices that any well-equipped engine rebuilding shop could handle.

Wilson Bros. Engineering, with a long-time reputation for quality performance engines, handled the machining and assembly work. The engine was disassembled, the hot tank was cleaned, and the reusable components were Magnafluxed. Close attention was paid to the crankshaft because they have a history of developing cracks. Wilson Bros. "Squared the block"; that is, they machined the cylinder head surface to provide an equal deck height at each of the four corners. The heads were also milled to a flat configuration. Even though these milling operations most likely upped the compression ratio by maybe half a point, it was not done for the increase in compression, but to ensure equal combustion chamber volume and a good, true sealing surface between the cylinder head and block. After the block was bored .030 oversize and finished on a Sunnen power hone for the proper piston-to-wall clearance, the main bearings were line honed. It was fitted with Federal Mogul bearings, and the crankshaft was ground for .002- to .0025-inch and .0025- to .003-inch clearance on the rods and mains, respectively.

The crank's oil holes were chamfered to ensure full oil-volume delivery. The connecting rods were reconditioned, Magnafluxed, and sent out to the balancer along with the rest of the reciprocating component parts, including the pressure plate. The pistons are TRW forged with Sealed Power moly-coated rings. The gasket set was a Fel-Pro. Again, pay particular attention here because there is an early and late cylinder-head design. If you pick the wrong gasket, you'll find water in the cylinders. The camshaft is often referred to as the "brain" of the engine because it basically determines horsepower and torque output and at what rpm. After a lengthy discussion with Schneider Racing Cams, a 131H grind was selected to fit our needs. Since our needs also included a higher-rpm range than the stock IH valve springs could handle, Wilson Bros. did some checking and found that springs and retainers designed for a big-block Chevy would work just fine. These provided a seat pressure of 95 psi and an open pressure of 280 psi. For lifters, Sealed Power's were chosen, as recommended by the cam manufacturer. Wilson Bros. did a quality valve job along with some special cuts for P.C. oil seals and the fitting of bronze silicon valve guides.

The completed exhaust system included a set of Stan's headers pushing through 2 1/2-inch exhaust pipe and a pair of turbo-type mufflers. While we're speaking of exhaust, IH has several configurations in exhaust manifolds to choose from. Bigger is better. If you choose to use cast-iron manifolds, pick the ones with a three-bolt header pipe flange over the two-bolt design. The headers come awfully close to the starter solenoid, so after frying our original one we built a heat shield that allowed a 1/4-inch air gap between it and the headers.

For the ignition system, we wanted an update to an electronic system, but we felt that the stock electronic system lacked reliability. We finally settled on an Allison XR700 for two reasons: We had excellent success with one on an offroad race car; and, in case of a failure, the stock point setup could be replaced because the Allison unit made use of the original distributor. Naturally, the distributor was rebuilt, but the advance rate was left stock. That may be something to play with at a later date because we've found the engine to be very susceptible to overall ignition timing. Every engine reacts a bit differently, and since I didn't index the timing mark on the front pulley, I won't give you a figure. I time mine by advancing the distributor until it pings under a heavy load on a hot day, then retard it a bit until it just stops pinging. To top off the engine, my choice was a spread-bore four-barrel manifold. The small primaries give excellent low-speed, rock-crawling performance and improved fuel mileage at cruise, while the much larger secondary bore is large enough to provide high-rpm breathing. The Thermo-Quad is a good carburetor and will give excellent results. Because I had a new Holley spread bore, I chose to use it, but I had to make extensive modifications to it. These included a change of fuel bowls, modifications to the delivery system, and spacers below the carb and between it and the air cleaner. My choice for an air cleaner was a K&N unit in a Holley canister.

Was it all worth it? As Little Beaver used to say to Red Rider, "You betchum!" We have an engine that will pull high gear from a dead stop, has lots of midrange torque, and will pull 5,000 rpm upon demand. Fuel mileage will depend upon how you drive, where you drive, and how much weight the engine has to pull. In a Scout, we're sure our engine would do a presentable job of showing the competitors the "short way home" and still deliver 16 to 17mpg with no trouble. In my heavyweight IH crew cab truck, street mileage is around 12 mpg. With my fifth-wheel trailer and a total of nearly 19,000 pounds of weight, I average nine mpg at legal limits and about 7-1/2 when I am in a hurry.


Wilson Bros. Engineering

12380 S. Fern Ave.

Ontario. CA 91710


Schneider Racing Cams

1235 Cushman Ave.

San Diego. CA 92110


Stan's Headers

5811 East Imperial Hwy.

South Gate, CA 90280


Allison Automotive

720 East Cypress Ave.

Monrovia, CA 91016


Reproduced from: 4x4 ANSWERBOOK, pp. 16-17

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