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ME Channels / Machines & Automation

Shop Solutions: Advanced Honing Masters Engine's Peaks and Valleys

Dart Machinery (Troy, MI) is a world leader in manufacturing engine blocks for racing and high performance enthusiasts, as well as replacement blocks for a variety of Detroit V-8 engines. Dart uses the SV-20 advanced flexible honing system from Sunnen Products Co. (St. Louis) to “master the peaks and valleys” in honing cylinder bores to produce custom results with near-mass production efficiency.

“Advanced honing provides a key differentiator for maintaining a competitive advantage and achieving greater efficiencies and flexibility in processing an ever-changing mix of blocks,” said Dick Maskin, Dart founder and president. “A new SV-20 honing system from Sunnen enables high-precision, highly-flexible honing of a wide range of block designs and metallurgies in a single continuous process without the need for stone change,” Mastin said. American-made in St. Louis, the SV-20 replaces a more expensive, European-built honing system that “just wasn’t a good fit for our production, not flexible enough,” he said.

Maskin started Dart in 1981 in a two-car garage in Oak Park, a Detroit suburb, and has grown it into the leader in manufacturing racing and high-performance engine blocks, heads and other components. The company does its part to keep Detroit “Motor City” with both a technology center and manufacturing facility located in the metro area. Today, 95 Dart employees make about 8000 blocks and 16,000 heads a year for drag racing, circle track racing, road racing, and high-performance custom cars, as well as marine and industrial power applications.

Dart Machinery technician Bob Dimitrijevich installs iron sleeves in a cast aluminum block while a billet aluminum racing block awaits installation. Aluminum block bores are honed for size and geometry before liner installation.

The manufacturing facility operates three shifts, six or seven days a week depending on production volume, with 26 large Makino CNC machining centers churning out blocks, heads and manifolds. Customers can choose between seven different base block designs covering big block and small block sizes, all evolved from NHRA pro stock V-8 experience. “That’s where all the technology comes from,” said Maskin, whose own engine creations achieved drag-racing’s first 300 mph quarter-mile run and four-second Funny Car elapsed time.

“We produce custom in volume,” said Maskin. Blocks are manufactured to customer order in type and material, bore spacing, cam location, bolt pattern, deck height, lifter location, oil pan bolt pattern, metric or US dimensions—“just infinite variation and specialization.” Dart makes blocks in various grades of iron (cast iron to CGI) and in aluminum with iron-sleeved cylinder bores, including blocks machined from forged and heat-treated aluminum billets.
A Chevrolet performance small block is being honed at Dart Machinery in the new SV-20 flexible honing system from Sunnen.
Dart combines two advanced technologies—diamond honing abrasives driven with a programmable spindle, followed by profilometers to measure the peaks and valleys of cylinder surface finishes—to replicate “best” block finishes and ring seal. “Experienced racers have always had their favorite blocks, ones that ran better than others,” said Maskin.

“We’ve learned through experience that it wasn’t the block that made the difference, but how your honing process worked for that exact block, since similar blocks might produce much less horsepower. Once you understand the finish you need from honing—and we know these numbers now thanks to profilometers—you can make the bad blocks good, too. We use honing to achieve the ideal Rvk [valley depth average], Rpk [peak height average], Rk [core roughness depth], and crosshatch to finish a block for a given application,” Maskin said.

Knowing the desired result, the honing process can be tweaked to achieve the result in any block. “If you go from a 200 brinnel block of cast iron to a much tougher CGI [compacted graphite iron] block, you need to know how to achieve your finish numbers in the different materials,” said Maskin. “Finishes also must account for the type of fuel burned in the engine, which could be alcohol or natural gas.”

“Honing is all about sealing the rings to the cylinder wall,” said Maskin. “The key is valley depth. Too deep and you have too much oil in it, slowing the engine down with friction. Too little valley, and the rings can hydroplane across the valleys and you lose seal. Then, you have to run thicker oil. Unless oil can reside in the valleys, it sits on the cylinder wall and must be thick not to be torn off by the rings. We think valleys need to be in the mid to high 30 microinches (0.000030"/0.00076 mm) to really seal a race engine strongly, and deeper in the mid to high 40s [microinches] for a more conventional engine.
Sunnen’s two-stage diamond abrasive honing tool does roughing and finishing with 220- and 500-grit abrasives without pause for stone change, making a wide range of finishing options available to Dart Machinery.
“For some blocks using today’s steel rings, we hone for peaks of 12–15 microinches (0.000012–15"/0.00030–0.00038 mm) or smoother. When we turn the short block over manually with a wrench, the rings will knock the peaks down to 5 [microinches] or less before we ever start the engine, but the valleys remain. We may not always take the peaks off during honing. If you ball-hone or sandpaper, thinking you’ll accomplish this, you’ll simply reduce valley depth and the engine won’t run as good. In our experience, if you go smoother on honing peaks and valleys, the finish won’t last as long. Starting with a rougher finish, the block is going to wear in and be sealed up so tight it will surprise you,” Maskin said.

The SV-20 honing system gives Dart the flexibility to efficiently process any engine block in any material and hardness. “There is no typical production run for us,” said Maskin. “We can put a new block on the SV-20, once the program is written, and no machine can make a cylinder rounder or straighter. The finish is all based on programming. If you know where you want to go, you can get there,” Maskin said.

“Computer control has taken much of the black art out of honing. Machines like the SV-20 produce a finish and size that previously required a very talented machinist. If you have to hone different blocks with different material content, like we do, the newer equipment is significantly better,” Maskin said. The Sunnen SV-20 honing system uses programmable control to replicate “best” engine parameters and produce expert results with minimal operator expertise. ME

For more information from Sunnen Products Co., go to, or phone 800-325-3670


This article was first published in the June 2014 edition of Manufacturing Engineering magazine. Click here for PDF.  

Published Date : 6/1/2014

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