Building the Better Straight Six Engine
Hesco: Expert Engine Building in Profile
Sometimes profiling a builder is as simple and natural for us as turning the ignition key on one of our vehicles. Hesco has been building engines for more than 34 years. Why does this interest us? Hesco builds Jeep engines. How good are they? We figured it was a good indication when Jeep asked Hesco to help create Jeep's engine manuals. Hesco is also credited with supplying engines for 13 Daytona and NASCAR wins, and preparing engines for Chrysler Motor Sports' desert racing.
The straight-six 4.0L H.O. engine for Jeep has been one of the workhorses for the company since its release. In factory form, the engine cranks out approximately 190 hp and 224 lb-ft of torque. The engine responds exceptionally well to performance modifications. Hesco's rebuilds have consistently turned out powerplants with massive amounts of additional power. The company's stroker engines with CNC cast-iron heads put out approximately 270 hp and 333 lb-ft of torque. Stroker engines fit with Hesco's aluminum heads crank out 300 hp and 365 lb-ft of torque.
Because of Hesco's reputation and quality product, and because we only like to tell you about products that actually work, we gave our contact at Hesco, Bennie Fulps, a ring and had him walk us through an engine build. This information should help you in selecting a new engine for your Jeep or give you some pointers on your next home build.Engines reborn at Hesco are hand-selected cores from select suppliers. Each block, head, connecting rod, and crankshaft is heavily scrutinized after cleaning. We were told that only the best cores are selected to become a Hesco rebuilt engine.
All components are hot-tanked twice and then dipped in an anti-rusting solution before inspection. Each block is bored to whatever specifications a customer has requested for their new engine. Torque plates are installed for the block deck and water pump to ensure a bore. After the block has been bored and honed, it is hot-tanked again to remove the honing oil and any debris from boring the cylinders. Once this process is complete, the block is hand-washed and blown-dry. It now begins its journey to a final inspection before being selected for a new life.
The block is then placed on a stand in a temperature-controlled build room. It will be mocked up with the crankshaft, piston, and rod. The deck height is checked and the block disassembled. It is removed from the engine stand and placed in the decking machine, where a predetermined amount of material is removed to obtain a set compression ratio. At this time, a Hesco machinist works a little magic with a die grinder in strategic places in the block. The block again goes through a cleaning and hand-washing process.
The block is now ready for a final trip to the build room, where it is placed back on an engine stand. Next the cam bearings and freeze plugs are installed. Assembly lube is applied to the cam lobes, and the camshaft is installed in the block after having been through a cleaning process. All internal engine parts go through a cleaning and inspection period. Nothing is taken out of its package and installed without having been hand-washed and inspected.
The crankshafts used in Hesco's engines are hand-selected, inspected, and magnafluxed. They are checked for straightness and any visible flaws. If necessary, they will be turned. They are turned to very precise tolerances, as dictated by the machine shop manager. The crankshafts are then deburred, balanced, and shot-peened. Once these steps are complete, they are cleaned and blown-dry, and inspected by a machinist.
The connecting rods used in Hesco's engines are one of the most scrutinized pieces in the engine. They are hand-picked for weight, length, and straightness. They are then placed into matched sets. Each connecting rod is deburred, the beams polished and shot-peened. If the rod is destined for a stroked engine, it will go to the CNC machine, where the pin end counter weight is precisely machined off for clearance to fit the forged stroker pistons. Once these steps are complete, the connecting rods are fitted with ARP rod bolts and each end machined to strict tolerances for the particular engine they are to be used in. The rods are then balanced and washed before final inspection and assembly onto the pistons.
All pistons go through the same routine, whether they're forged pistons destined for a race engine or a stock cast piston used as an everyday driver. They are checked for uniformity in weight and size. The quality of the casting or forging is checked and the pistons deburred. All forged pistons and any cast pistons a customer requests are sent to a ceramic coating room.
Once there, the piston rings' lands are taped, and the piston domes and skirts are media-blasted in preparation for coating. The pistons are washed in a solution and dried. They are preheated to a minimum of 90 degrees F before any coatings are applied. Once they are at the appropriate temperature, a ceramic coating is sprayed on the domes. A DFL moly coating is sprayed on the piston skirts. The tape is removed from the ring lands and the pistons baked at a minimum temperature of 300 degrees F for one hour.
Back in the machine shop, the piston pins are fitted to their respective tolerances using a Sunnen connecting rod machine. Then the pistons are balanced, cleaned, and given a final inspection. The pistons are then pressed on their respective connecting rods using Sunnen piston pin lubricant. The piston rings are removed from their packaging and each fitted to their cylinder. Piston rings are placed in the cylinder they best fit. The end gap is precisely measured on each ring to insure a perfect fit. The results are recorded on the build sheet. The rings are then installed on the pistons.
The main bearings are now installed in the block and main caps. The caps are placed in their respective location and torqued to spec. The counter bores are each measured and the numbers recorded on a build sheet. The crankshaft main and rod bearing journals are measured and these numbers are also recorded on the build sheet. Each connecting rod with its two bearing halves are assembled, the rod nuts are torqued, and these numbers are also recorded. With these figures, the engine builder is able to measure the oil clearance of each main and rod journal. If the clearance is to spec, he will prepare for final assembly of the short-block. The main bearings will get a generous amount of Redline Assembly Lube before the crankshaft is installed in the block. Before the crankshaft is installed, the upper half of the rear main seal will be installed. The lip of the seal will have a slight film of engine oil applied where it contacts the crankshaft to prevent tearing the seal when turning the crankshaft during assembly.
The crankshaft is installed and torqued to factory specifications. The crankshaft endplay is recorded on the build sheet. The piston pins are oiled to prevent galling during start-up and installed in their respective bores using a ring squeezer and piston installation hammer. The piston hammer is a soft dead-blow-type tool designed to prevent damage to the pistons and coating during installation. The connecting rod nuts are now torqued to ARP specifications included with all their fasteners.
A three-piece double-roller timing chain and gearset are now installed. The camshaft is degreed according to what the engine is going to be used for. It is set up at different specifications depending on if the vehicle has a manual or automatic transmission and if the engine is being built for low- or high-end torque. This is accomplished using a degree wheel and dial indicators.
Once the camshaft is properly installed, the timing cover is installed. The oil pump, having being taken apart and inspected, is coated inside with a film of assembly lube and reassembled. The pump is installed and the bolt torqued to factory spec. The oil pan is then installed and the bolts torqued.
The heads Hesco uses go through the same regime of inspections and washing. The valveguides are measured; the valve stems of the new valves are also measured for uniformity. If the clearances are correct, the machinist will proceed with a standard three- or five-angle valve job. This is dictated by the customer or what the engine is being used for. Very few street engines ever gain any real benefit from a five-angle cut. Once the valve job is finished, the valvespring seats and guides will be machined for the proper spring height and tension. This figure is determined by the valve lift of the camshaft being installed. The amount of material removed from the valveguide will be the same as removed from the spring seat and is done so the valvespring retainer doesn't contact the top of the seal and damage it.
Once the valves have been faced to match the seat cut, a set is installed so the combustion chamber volume can be measured with a device called a burette. It is marked in cubic centimeters and will usually have a liquid volume of 250 cc's. Once the volume is measured, it is compared with the piston and chamber volume to arrive at a compression ratio. The volume of the head gasket is also figured into this equation. The head is then milled to a specified chamber volume for the correct compression ratio. The head is then hand-washed, blown-dry, and assembled. The valve lifters are coated with assembly lube and installed on the camshaft lobes.
The cylinder head is then placed on the block. A small amount of PST liquid Teflon is applied to the threads of each head bolt before being installed in the respective holes. They are torqued in three stages with a final setting of 110 lb-ft on each bolt except No. 11. The final torque for this bolt is 100 lb-ft. Assembly lube is applied to each end of the pushrods and they are installed with one end on each valve lifter. The rocker arm assemblies, having been washed and dried, are next in line. The rocker pivots are coated with a film of assembly lube, as is the tip of each valve stem.
The rocker arms and pivots are installed in pairs. A dial indicator is used during the bolt tightening sequence to measure lifter preload. Too much preload and the valve will be held open and the engine rotates, resulting in a loss of compression. If adjustment of the preload is necessary, shim kits are available from camshaft manufacturers, or AN washers in 0.030 and 0.060 may be used. This measurement is recorded on the engine build sheet. Refer to the Jeep manual for the specifications on bolt torque and preload. Once the rocker arms are properly adjusted, the valve cover is installed. The oil filter adapter is installed with a new oil filter that has been filled with fresh oil. A mechanical oil pressure gauge is attached to the oil pressure sending unit block next to the oil filter. The engine is filled just below the add mark of the dipstick. The oil pump shaft is turned by hand until pressure registers on the oil pressure gauge. The pressure is also recorded on the build sheet. Every specification of an engine is recorded on the engine build sheet.
The engine is then sent to the engine dyno room, where the camshaft will be properly broken in and the vitals recorded on the dyno computer. Once the camshaft is broken in and the engine inspected, it will be run to ensure the power levels are as expected for that particular engine combination. Obviously, we can't cover everything in this story - and there are trade secrets that drastically increase performance that Hesco told us not to reveal - but once the operator is satisfied the engine is of the expected power and quality, it will be removed and installed or shipped to the customer.