Engine Assembly Basics -- Technical Article -- Engine Masters Magazine

We know there are many performance enthusiasts who dream about putting together a high performance powerplant, but don't quite have the confidence or experience to jump in. What are some of the tricks, techniques, and tools required to successfully build an engine? With this story we will launch a series of articles aimed at answering just those types of questions. Without a doubt, building a performance engine requires a sound understanding of the fundamentals of assembly, answering the question of "how to do it" as much as "what to do." That's the kind of practical information we are looking to provide.

To really get into the details of how it's done, there's much more content than can possibly be covered in a single story. We've broken down the building process into bite-sized pieces, and will cover an aspect of engine building technique in each following issue. We aren't necessarily aiming at turning our readers into race engine machinists, but hopefully we will provide the background required to assemble a great engine in your own garage. We'll start this month with the short-block, and move on to the cam and valvetrain in the next issue, followed by the top end. We encourage feedback from our readers, so if you have an area of engine building you'd like explained in detail, contact me at steve.dulcich@sorc.com.

Mock Build-up
Before even thinking about breaking out the tools for final engine assembly, step one is to perform a trial or mock-up assembly of some of the major components. The goal here is to identify any problems that will arise in assembly, and take care of them before the real build begins. Usually, the areas to focus on here are clearance issues where non-stock components are being used. Some examples include rod and crank clearance with stroker cranks, lifter and link-bar clearance with roller lifters, or cover clearance when converting to a belt drive. Just about anywhere non-stock parts are being used, take the time to check the fit before final assembly.

Essentially, the mock-up is a test fit of the components, checking for problems as the parts move through their range of motion. It isn't necessary to fully install the parts or torque the fasteners for many of these checks. For instance, for checks like piston deck or rod clearance, the crank can simply be installed with a pair of maincaps and bearings, including the thrust bearing. A piston/pin and rod assembly can be temporarily positioned without the pin locks or rings to verify crankcase clearance, moving the piston from hole to hole. Similarly, a belt drive adapter may just be laid into position, to check for any clearance problems that will hang-up the casting.

The reason for the mock-assembly is that the remedy for most of the problems encountered will usually involve grinding or cutting, so it pays to find these potential problems before things are cleaned up and the engine is partially built. Key items to check in the short-block include rod clearance, rod side clearance, crank counterweight clearance, piston deck height, cam timing, and skirt to counterweight clearance. Top end checks include things like the piston to head clearance, valve to piston clearance, valve lift, retainer to guide clearance, valvetrain geometry, and intake manifold alignment. Several of the checks will involve precision measurements. Many of the precision tools for the job can be had at budget prices from Powerhouse Products or Harbor Freight Tools.

File-Fitting Rings
The end gap of a set of compression rings represents a leakage path for the gasses in the cylinder, and that applies to every phase of a four-cycles engine's operation. Minimizing this leakage is a means of improving the mechanical efficiency of the engine. Typically, file-fit rings are manufactured to a 0.005-inch larger diametrical specification than the bore, allowing the ring end gap to be custom filed to a desired end gap. Adequate gap is required to prevent the ring ends from butting in operation, so the desired specification will vary, depending upon the engine's usage. File-fit ring sets will usually come with an instruction sheet specifying recommended end gaps for varying applications. There are numerous tools and techniques that can be used for file-fitting rings, from simple hand files, to hand-cranked filers, to more elaborate power-driven units such as ProForm filer used here. All will get the job done, it's just a matter of time invested and what you're used to.

Custom gapped rings can represent a measurable increase in power, but a botched job can lead to a power loss or engine damage. Here is how rings are gapped and what to look out for.

Block Prep
The final build-up begins with the block prep. A block may be fully prepped from the machine shop, and ready for assembly. However, in most instances, the builder still has work to do after the major machining is complete--particularly if the engine is being built from a used core. The final pre-assembly block prep should be done after all of the mock-assembly checks are made. Although it isn't absolutely required, the first step is to perform any deburring or grinding operations, such as removing casting flash, radiusing or enlarging oil passages, or smoothing drain-back areas in the lifter valley. With used blocks especially, the threaded holes in the block should be chased with a bottoming tap to clean debris from the threads. Once all of these debris-creating jobs are completed, the block can be cleaned and painted for final assembly.

Crank Installation
The first major step of engine assembly is installing the crankshaft. While it is simple enough to insert the bearings and drop the crank in place, there are certain checks that need to be made before all is known to be right. Some of these checks, such as runout and bearing clearance could be made during the mock-up assembly, but the crank end-play needs to be verified after the main caps are torqued in place. Here are some points to pay attention to when installing the crank.

Reciprocating Assembly
Loading the pistons and rods into the block marks a major milestone on the way to completing a build. There are several areas where a builder can get into trouble here, so careful assembly procedures are a must. It's best to first fully assemble all of the piston/rod assemblies, complete with rings, bearings, and lube, before knocking the first one in a hole. The orientation of the parts is important here. If using the stock rods, they should be numbered when the engine is disassembled, so that they can be replaced in the same position and orientation upon re-assembly. Many OEM rods are marked by the factory; if not, mark both the cap and rod.

For the beginning builder, pressed pins are best left the to machine shop, but the rod/piston orientation should always be checked. If putting together rods with floating pins, the rods need to be oriented correctly when the pistons are hung. Most rods, including aftermarket units, have a large chamfer on one side of the big end, and little or no chamfer on the other side. The rod needs to go in with the large chamfer to the cheek of the crank journal. A high quality lube such as Torco Assembly Lube from Valco Cincinnati is best for the pins. Lube the bores of the piston and rod, as well as the pin itself. Tru Arc style pin locks are easily installed with snap ring pliers, however most piston manufacturers these days supply Spiro Lox. Spiro Loxs are nearly failure-proof.

It pays to take extra time in getting organized for this part of assembly, laying all of the components out on the workbench, in an order corresponding to their final position in the engine. Each hole should have a piston, rod, rings, and wristpin specific to its cylinder, laid out in order. The job is to load these parts into eight assemblies, and then install them in the engine.

Master engine builders can detect potential problems while assembling an engine just by feel. As each operation is performed, check the parts and feel for any snagging or binding. Make sure that the bearing seat fully into position in the rods, the rings fit the grooves smoothly, without hanging-up, sticking, or binding, and the pin retainer locks are seated fully in their grooves. There really is no margin for error in installing the reciprocating assembly. Each part should fit together without having to be forced into position. When the pistons are installed in the block, care must be taken not to hang a ring up on the deck, which can easily bend or break a ring. If something doesn't feel right, stop and investigate. Get the short-block done, and the engine project is well on its way to completion.