Cylinder boring and honing is the heart of most engine builders’ operations. The equipment you use will have a lasting effect on the quality of the product your shop sends out the door on a day-by-day basis. While equipment varies from manufacturer to manufacturer, so too do your needs for a specific type of machine. Some shops are so cramped for space that you can barely find a lane to walk, let alone fit a large single-purpose boring machine.
One- and two-man shops do not have the same needs as a production engine remanufacturer (PER) with 100 employees. These smaller shops often can’t justify the purchase of a top-of-the-line boring or honing machine with all the latest “bells and whistles.”
Large remanufacturers, however, generally have the space and produce enough volume for a stand-alone, single-purpose machine to make sense. Plus, many PERs run machining operations simultaneously, therefore a multi-purpose boring/milling machine would leave many employees standing around.
Smaller custom engine rebuilders (CERs), on the other hand, may benefit greatly from a multi-purpose machine.
That’s why it can be helpful to be reminded that there’s a wide variety of boring and honing equipment available today, and for every price range. So if you’re still using that 30-year-old boring bar and hand hone, now may be the time to look at your options.
Boring has been a mainstay of the engine rebuilding process for quite some time. The principals of boring have not changed very much over the years, however, the tooling and equipment have evolved to keep pace with both original equipment manufacturer advancements as well as the demands of racing.
Boring out a block to accept oversize pistons or to salvage an old core or even to increase displacement is a regular operation in most engine building facilities. On the performance side, boring a block to accept hardened cylinder sleeves is opening up many new opportunities for shops capable of doing this work. Sport compact engines have been utilizing sleeves for years to better handle the high loads created by forced induction systems such as turbochargers, superchargers and nitrous oxide.
“Compared to the equipment of years past, all the new equipment uses air-float boring bars which float across the ways and can center itself over the cylinders, whereas older boring bars were portable and bolted down to the deck of the block,” says Winona Van Norman’s Ed Kiebler. “The new bars use indexable cutter bits instead of brazed-on cutter bits. We use coated carbide bits.” Carbide bits are not as expensive as CBN or diamond bits but also don’t have as long of tool-life or cut as fast.
“Older machines were designed to use brazed-on carbides; therefore the speeds and feeds were not as fast as they are now. Today’s indexable carbides with the new coatings on them can utilize faster feed speeds and higher rpms to get the job done more quickly than in the past. Older machines just aren’t capable of that. And, honestly, there are some machines out there that are just absolutely worn out. So it’s much harder to hold today’s tolerances with these machines,” explains Kiebler.
Kiebler and other experts interviewed for this article explain that one of the biggest reasons equipment and tooling has gotten better is because OEMs have tighter and tighter tolerances on their new engines. “Once upon a time, you fitted a piston into a cylinder bore with anywhere from .0025? to .004? clearance,” Kiebler explains. “Today, pistons are actually zero-fit in some cases. You have much less room for error and tolerance stack up than you once did.”
Technology advancements now allow for higher spindle speeds and feed speeds to get the job done faster, say the experts. The other part of that equation is that machines are designed better, with better materials, so they generally outperform older machines quite substantially.
For some small shops just entering the market, they may find that a portable boring bar is the most economical route.
There are a few limitations to your capabilities when using a portable bar, say equipment experts, but they do offer a way to get into the business for less financial investment. If you are interested in the portable bar, spend a little more money and purchase a complete machine with a stand and an air-float system. The stand will prove to be an invaluable part of a portable boring bar system, especially when used on newer engines. Experts say it is not recommended to mount the bar on the deck of a new-style thin-wall engine block because it could cause bore distortion.
An ideal option for some smaller, more specialized shops may be a multi-purpose boring/milling machine. Multi-purpose machines take up much less space in the shop and, for the price of one piece of equipment, you get virtually two machines. Because smaller shops typically don’t do as much volume as larger shops, they frequently are looking for machines that do precision work rather than offer sheer speed.
For the PER and those shops looking for speed and automation, there are several choices. There are boring machines to fit every engine bore size so you need to know what type of work you do most. If you primarily build smaller automotive engines then a machine capable of boring a large diesel engine may not be the best choice for you.
Many of the automated boring machines have programmable boring cycles and automated centering cycle, which helps aid workflow.
The biggest key to profitable and successful engine rebuilding is not so much the boring but controlling the the honing process, according to experts.
Honing is a metal removal process that engine builders use after the boring process to obtain precise bore geometry. Today’s engines require straight and round cylinders with the proper cylinder wall finish so that the rings don’t wear too much or carry too much oil. Honing is a productive way to improve the bore geometry and surface finish. It brings the peaks and valleys down to the optimum level for oil retention and bearing load.
“About 7 or 8 years ago I had shops telling me they couldn’t afford honing machines and didn’t think there was a profit in it,” says Rottler Manufacturing’s Michael Mohondro. “That didn’t make sense to me because honing is really the whole heart of the rebuilding process. You have to have compatibility between the rings and cylinder wall.”
Most engine builders now use some type of honing process to finish cylinders. But there are several levels of honing equipment, so it depends on what a shop can afford. Some machines are fully automated and require almost no operator attention, while other machines are almost completely manual.
Sunnen’s Tim Meara says the St. Louis-based company has just introduced a new hone. “It uses a two-spindle mechanical system, which allows you to separately control stroking speed and hone head speed,” Meara explains. “It eliminates one of the problems caused when some hones that use a pneumatic stroke become spongy, which can leave an inconsistent finish on the cylinder wall.”
One of the most dramatic changes in honing in recent years has been the switch to diamond abrasives. Conventional vitrified abrasives are still effective for finishing cylinders but they wear almost as much as the metal you are finishing, say some experts. You have to monitor the wear and dress the stones often to avoid cylinder taper. With diamond abrasives, they last longer and bore more consistently for the life of the tool. The coolant that is used when honing helps keep the cutting action cool therefore it doesn’t transfer heat into the cylinder. When you use diamonds for honing, most experts recommend doing a final plateau hone to remove the folded edges and debris left over from the diamonds.
As with boring machines, there are several different levels of honing machines available. Some manufacturers have a niche in the small shop market and therefore produce very affordable equipment without many accessories. These basic honing machines have many of the same features as high-end machines minus most of the automation. Most of the automated machines have on screen readouts to show exactly where you are in the honing process and will automatically dwell if necessary. Dwelling occurs when a high spot or taper in the cylinder is located by the machine. The hone head will hold its place on the high spot and rotate for a given length of time to straighten the cylinder.
Today’s honing and boring equipment is much more automated and precise than machines from decades past, however there are shops that won’t be able to justify the expense just yet for this automation. There are still some manufacturers that only specialize in manual equipment, which can be a very viable option for smaller shops. On the other end of the spectrum, if you’re ready to step up to a higher level of performance and automation, get in line because the demand for these machines is growing.
For information on reaching the manufacturers of the products included in the photos, visit the Engine Builders Buyers Guide, available exclusively at www.engine-builder.com.
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