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.
To get an accurate reading...
To get an accurate reading of the gap, the ring must be inserted square in the bore. A ring-squaring tool or an inverted piston with a second ring installed as a stop can do the job. Before filing, the ring's end gap may butt solid; never force the ring in. The end gap is measured with a feeler gauge. Work up from a smaller feeler gauge a thousandth at a time until the next one won't go in. Closely examine the end gap by feel with the feeler gauge as well as by sight to judge whether the end gap is parallel.
We used the ProForm filing...
We used the ProForm filing tool to size these rings. This tool is first set up to square the rings to the abrasive wheel by adjusting the eccentric locator. The dial indicator will read how many thousandths have been taken off. It pays to re-measure the ring in the bore several times to check the gap, and make sure it is parallel. It's better to stop short than to take too much off the ring.
A hand-crank wheel, like this...
A hand-crank wheel, like this one from Summit Racing, is a lower cost alternative, but requires repeated trial and error test fitting and measuring to sneak up on the desired fit. Some builders will file from only one side to manually align the squareness of the cut. Always cut with the wheel turning inward towards the center of the ring, as an outward cut will flake the moly from the ring face around the gap. My favored technique to control the parallelism is to press the ring firmly into the stop pins if more material needs removal from the outside of the gap. Alternatively, to take more from the inside of the gap, the ring is pressed lightly against the stop pins and squeezed more tightly in the center. You have to develop the feel.
After filing, the ring will...
After filing, the ring will have a raised burr at the cut edge. This will cause the ring to hang-up in its groove, and can also damage the piston. A small, fine, needle file can be used to lightly de-burr the edge, but don't chamfer it. We used this de-burring tool from Childs & Albert, which works nicely. After filing, clean the ring and mark it with a felt pen with the number for its corresponding bore.
In used blocks threaded bolt...
In used blocks threaded bolt holes can trap considerable scale, rust, and gunk. Chasing the threads will let the fastener run-in smoothly, and torque accurately, while preventing trash in the threads from making its way into the engine assembly.
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.
Clean the block thoroughly....
Clean the block thoroughly. I like to start with a carb cleaning solvent in the blind bolt holes and follow with a scrub-down with an engine degreasing solution like Gunk. Bore brushes are helpful in the galleries and passages. Finally, a good cleaning with warm soapy water, and a clean rinse has the block spotless. Quickly wipe the bores and machined surfaces with a rust inhibitor, such as WD-40, and blow the block dry with compressed air.
Although the block can be...
Although the block can be painted as an assembly, painting the engine parts separately leads to a more detailed look. Spray-can engine enamel is the norm here, though my preference for lasting show-quality looks is automotive epoxy primer followed by custom mixed automotive urethane. Mask the block thoroughly to avoid overspray.
Cam Bearings are relatively...
Cam Bearings are relatively easy to install, if you have the appropriate drivers. This universal tool from Powerhouse Products handles any cam bearings. Make sure the cam bearings are in their correct location, and clocked for proper oil hole alignment.