7.3L Ford Engine Rebuild Project: Domestic Diesel

Some time back, John Ferguson, the owner of Domestic Diesel in Chino, California, was approached by a long-time customer looking to unload a well-used 7.3L-powered Ford pickup from his work fleet. The clock showed a hard-earned half a million miles, hardly ideal under typical circumstances but it was the service performed by Domestic Diesel over the years that had helped get it there. The service history and the relatively low asking price presented Ferguson with an offer too good to turn down and in no time Domestic had a new but seriously worn-out shop truck. The most obvious issue was undoubtedly going to be the high-mileage motor and trans but at least it was a case of better the devil you know than the devil you don’t. Its potential was abundant and thus, a project was born.

When we heard about this 7.3L Ford engine rebuild project, we jumped at the chance to provide a detailed look at what it takes to do a better-than-new rebuild on a diesel engine. After all, how often does anyone get the chance to see the bare bones of these motors, motors that, more often than not, last longer than most cars?

1. Our 7.3L Ford (International) V-8 diesel was sent to L&R Machine where it was completely stripped and cleaned. Here you see the block coming out of the hot tank.

2. Once clean it’s thoroughly checked for any cracks. L&R uses a very strong magnet and some iron powder for this, as cracks will show as an irregular pattern in the powder. Thankfully our engine block was crack free.

3. The block is put on a boring machine to ensure that all the piston holes (bores) are round, straight and of the same size. We tried for a .020 over, but .030 was required to ensure full cleanup. — 3. The block is put on a boring machine to ensure that all the piston holes (bores) are round, straight, and of the same size. We tried for a .020 over, but .030 was required to ensure full cleanup.

John’s crew began, of course, by removing the engine from the truck before stripping it down to the heads to ship off for a rebuild. For those in the know, this is called a long-block, as heads are included in the package. The well-worn powerplant was then sent off to L&R Automotive in Santa Fe Springs, California, for a complete rebuild.

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On receiving the 7.3L Ford (International) V-8 diesel, L&R stripped it down and cleaned everything in preparation for machining. The cleaning process, usually called “hot tanking,” is essentially where the parts are removed and then put into what looks like a dishwasher on steroids. The engine parts come out clean, steaming and grease free. From there, the parts are sent to respective workstations for the rebuild process; heads go one direction, and the block and related parts go another.

On the block side, the first thing that is done is a thorough check for cracks, a process called Magnaflux. L&R uses the old school method of using a very strong horseshoe magnet and iron powder. The magnetic lines are interrupted by a crack and this shows in the pattern the iron powder displays. There are more modern, electromagnetic kits available that essentially do the same thing. Once a block is determined to be crack free, it moves on to the machining center where it’s checked to determine the bore diameter and the taper of the cylinder. If it’s within machinable specs, the cylinders are bored out to accept slightly larger pistons. Typically engines are bored .030 over stock, and .060 is usually the maximum.

4. After boring the block’s cylinders, it’s then sent to the honing machine. Honing the cylinders makes them all the same size and provides a better surface finish. This ensures a good seat of the piston rings and a long engine life.

5. This Sunen bore diameter indicator is used to check the cylinder bore diameter and taper. It reads in at .0005, half a thousandth less than the diameter of a human hair. — 5. This Sunnen bore diameter indicator is used to check the cylinder bore diameter and taper. It reads in at .0005, half a thousandth less than the diameter of a human hair.

6. The crankshaft of the engine is the main rotating part. It rides on bearings that are supposed to take the stress and wear as the engine run. Unless you have an engine with a spun main bearing, a simple, light-touch line hone operation for the mains should be all your engine needs. If not, a line boring will clean up the crank journals. Here you see a line hone operation being performed by L&R on our 7.3L block. — 6. The crankshaft of the engine is the main rotating part. It rides on bearings that are supposed to take the stress and wear as the engine run. Unless you have an engine with a spun main bearing, a simple, light-touch line hone operation for the mains should be all your engine needs. If not, a line boring will clean up the crank journals. Here you see a line hone operation being performed by L&R on our 7.3L Ford block.

7. L&R also services the heads for the 7.3L refresh. First, the heads are stripped and cleaned. Then they are surfaced, as you see being done here. Surfacing the heads ensures a flat surface and a good seal of the head gasket. — 7. L&R also services the heads for the 7.3L Ford refresh. First, the heads are stripped and cleaned. Then they are surfaced, as you see being done here. Surfacing the heads ensures a flat surface and a good seal of the head gasket.

8. After a head is cleaned and surfaced, the valve seats are cleaned and resurfaced. The valve guides are also checked and renewed to spec if required. The final step is to install either new or reground valves in the valve pockets.

9. Once the valves are in place, the valve springs and retainers are installed and the heads are then ready to be bolted to the block. Refurbishing heads on lower mile motors is sometimes done, while leaving the bottom end of the motor alone.

Boring a cylinder leaves a rougher than ideal surface and so they are typically honed to final size. This gives a better surface finish for the piston rings to seat against as it’s critical the ring seal must hold back the high compression of a diesel engine and not allow it to blow past.

In addition to the cylinder bores, the block deck, or top that the heads bolt to must be completely flat. This surface is often refinished along with the actual cylinder heads to ensure proper seating. Essentially, every critical surface interface in your engine is checked and refinished as required for optimal precision. L&R is able to take this process to the highest level, as they are a small, detail-oriented shop and not a mass-production facility.

10. Here you see the two types of OEM piston rods used in the 7.3L diesel engines. On the left is one of the later model forged rods with cap studs. On the right is a powdered metal rod that uses rod bolts. The forged rods are preferable. The bolt-style rods have been tagged as “crack rods” by Ford diesel enthusiasts, as they tend to crack on the bolt interface, when the stock bolts stretch. APR offers a rod bolt kit for this type of rod, which greatly lessens this problem. The forged rods are still preferred, but your motor might not come with them. — 10. Here you see the two types of OEM piston rods used in the 7.3L Ford diesel engines. On the left is one of the later model forged rods with cap studs. On the right is a powdered metal rod that uses rod bolts. The forged rods are preferable. The bolt-style rods have been tagged as “crack rods” by Ford diesel enthusiasts, as they tend to crack on the bolt interface, when the stock bolts stretch. ARP offers a rod bolt kit for this type of rod, which greatly lessens this problem. The forged rods are still preferred, but your motor might not come with them.

11. Derek Ranney, manager and co-owner of L&R Automotive, inspects the new MAHLE pistons before they’re installed in our 7.3L diesel. L&R has been in business for 38 years and supplies engine parts as well as top quality machine work for all types of engines. — 11. Derek Ranney, manager and co-owner of L&R Automotive, inspects the new MAHLE pistons before they’re installed in our 7.3L Ford diesel. L&R has been in business for 38 years and supplies engine parts as well as top quality machine work for all types of engines.

12. After the refurbishing, the block is ready for reassembly. Here you see the camshaft being installed. Since this engine is for a shop truck, a stock profile camshaft was used. For more performance, you can look to the aftermarket for many different grind profiles.

13. Here you can see the piston oilers. These must be installed, and this is best done before the camshaft. Do not forget them if you’re doing the assembly work yourself.

With all the machining completed, engine reassembly can begin. While most folks don’t have the necessary skills or specialized equipment to perform the machine work, it’s not uncommon to see owners and shops do engine assembly themselves. In this case, Domestic Diesel opted to have L&R build the short-block and return it to them with the refurbished heads for final engine assembly.

A few upgrades were made, such as adding ARP main studs and an upgrade to the better quality 7.3L Ford factory forged rods. MAHLE pistons and rings were also installed by L&R.

Next time, we’ll show you the final engine assembly back at Domestic Diesel and cover a few must-have upgrades as they reenergize the truck and roll it in to a brand new career. DW