A “To The Bones” Engine Rebuild
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-million miles. However, 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 Diesel had a new but seriously worn-out shop truck. The most obvious issue was undoubtedly going to be the high-mileage motor and transmission, but at least it was a case of better the devil you know than the devil you don’t. The truck’s potential was abundant and thus a project was born.
When we heard about this 7.3L engine rebuilt 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?
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.
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 likes 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.
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. The ring seal is critical as it 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, the top surface 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.
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 APR main studs and an upgrade to the better quality 7.3L 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