Head and Block Resurfacing
The key to achieving high quality ultra-smooth surface finishes is using the right equipment, the right abrasives and the right resurfacing techniques
By Larry Carley
Resurfacing cylinder heads and engine blocks is an essential aspect of engine building today, whether the work is being done by a production engine rebuilder, a high performance specialist or small custom shop. Bimetal engines, multi-layer steel (MLS) head gaskets and tighter assembly tolerances make accurate surfacing more critical than ever before. The key to achieving high quality ultra-smooth surface finishes is using the right equipment, the right abrasives and the right resurfacing techniques.
According to more than one equipment supplier we interviewed, some shops are still trying to "make do" with outdated surfacing equipment such as broaches and grinders. But many of these shops are learning the hard way that yesterday's equipment can't deliver the kind of finishes that are required for today's engines. We're talking surface finishes with microinch roughness averages in the single digits on some late model engines as well as performance engines that are running MLS head gaskets. Even when a super smooth finish isn't required, having the flexibility to reproduce any kind of surface finish on any kind of cylinder head or block is a definite plus.
It's not surprising, therefore, that one of the most often replaced machines in shops today is surfacing equipment. Old broaches and grinding machines are being replaced with purpose-built high-speed surfacers that use long-life CBN and/or PCD inserts. Some of these machines are also multi-purpose machining centers with manual or CNC controls that can also be used for boring blocks.
Another improvement that often comes with an equipment upgrade is increased productivity. With the right fixturing, you can reduce the time it takes to mount the parts on the machine and set up your cut. If a new surfacer is easier to use and reduces setup and cycle times 5, 10 or even 20 minutes per job, the savings can really add up. Less time spent setting up and operating the equipment means more time for other work and/or a higher volume of jobs completed every day.
In a custom shop where you may be working on several different engines at the same time, a surface that can be reset quickly from one job to the next can keep work flowing smoothly instead of creating a bottleneck. Some surfacers can be set up and mill a head in five minutes or less, which is pretty quick in a fast paced shop. And if you're doing several identical heads in a row, the actual milling time may only be a couple of minutes. It all depends on the speed of the cutter head, the number of tool bits, the feed rate and how smooth the finish on the parts needs to be.
Most of today's high speed surfacers are designed to use CBN or PCD inserts in their cutter heads. CBN is the most popular choice for cutting both cast iron and aluminum because it can handle either material with ease. CBN also cuts cleanly at high rpm and can take the heat that's generated by higher cutting speeds. PCD is the best choice for aluminum but it doesn't work well on cast iron. Carbide is still popular because of its lower initial cost, and coated carbide helps extend tool life. But CBN and PCD generally lower operating costs over the long run when you consider how much longer superabrasives hold their edge and resist wear.
CBN inserts in a milling machine will typically cut 20 to 50 times as many heads as carbide inserts. The increased longevity of CBN improves consistency from one job to the next, and reduces down time for tooling changes.
Because CBN and PCD are designed for high speed milling, replacing the carbide inserts in an older surfacer won't necessarily achieve all the benefits that these superabrasives are capable of delivering - especially if an existing surfacer lacks the horsepower, rigidity or adjustability to operate at higher spindle speeds. Rigidity becomes a factor as operating speeds increase. A machine that lacks the required rigidity can't deliver ultra smooth finishes at high speed because there's too much movement between the workpiece, table and cutter head.
For example, a converted grinder may be able to mill heads and blocks. But the spindles and table drives in many of these older machines cannot hold close enough tolerances to achieve a really smooth, flat finish. One equipment manufacturer said grinding and milling machines that are more than five years old are probably incapable of producing consistent results and should be replaced.
Most of the surfacing equipment that's being sold to shops today has been redesigned for high speed milling with CBN and PCD. The machines have been beefed up with more powerful motors, heavier castings, electrically-driven ball screw tables, and tighter assembly tolerances. Some can hold machining tolerances to one tenth of a thousandth of an inch (.0001" )! You might not need that kind of accuracy for an economy smallblock Chevy V8 rebuild, but you might want that kind of accuracy for a megabuck high performance engine or even a late model high output overhead cam engine. There's no such thing as too much accuracy.
If you've come to the conclusion that your existing surfacing equipment just can't cut it anymore, here's a rundown of the latest surfacers.
Sunnen Equipment Company now has licensing agreements with both DCM and RMC to sell and provide technical support for the surfacing equipment manufactured by these two companies. DCM currently offers two versions of their surfacer (both share the same base): the HB-3810 manual surfacer, and the HB-3820 CNC controlled surfacer.
The Sunnen/DCM HB-3810 resurfacing machine is designed with state-of-the-art controls that simplify and automate the resurfacing process. Features include a powerful 7.5 horsepower motor with class 9 zero clearance bearings to stabilize the milling head (no variations in head height as the motor speed changes), a heavy spindle and dovetail column for added rigidity, a 14" cutter head that holds two CBN inserts, a precision ball screw drive on the X-axis for improved feed control, productivity and reliability. The machine has an automatic feed option available, and can also be configured for grinding. The HB-3810 can handle heads or blocks up to 38" long and 14" wide, and cylinder blocks as large as a Ford 460 (which can be rolled over to resurface both decks). The price for the HB-3810 is low to mid $20,000 range depending on how the machine is equipped.
The Sunnen/DCM HB-3820 is CNC controlled with a precision ball screws on both the X- and Z-axis, with accuracy to within .0001" (0.002 mm) on the Z-axis. The HB-3820 has the same size capacity as the HB-3810 but has a programmable drive that can be used for multiple cuts and automatic cycling. This surfacer is popular with racers because of its highly accurate controls and ability to achieve finishes as low as 4 microinches Ra. The price starts at $39,000 and goes up to the mid $40,000 range, depending on options.
The Sunnen/RMC-10VB and Sunnen/RMC-12VB are updated versions of an earlier machine that feature a variable spindle rpm ball screw table drive (which replaces the previously used hydraulic drive). The RMC-10VB has a variable speed (0 to 1,700 rpm), infinitely variable servo drive table (0 to 190" per minute) that also features an automatic cycle with stop. The machine can handle heads and blocks up to 38" long and 14" wide, with a maximum height of 21". The motor for the 14" milling head is rated at 5.5 horsepower. Price is $19,900 without fixturing.
The Sunnen/RMC-12VB is a larger 47" milling machine with a more powerful 7.5 horsepower motor and larger 15.75" milling head for CBN or PCD inserts. Maximum milling width on this machine is 15.75", and maximum work piece height is 29.50". The wheelhead speed is variable from 0 to 1,400 rpm, and table feed can vary from 0 to 130" per minute. Price is $23,900 without fixturing.
Rottler Manufacturing offers two groups of surfacing machines: the SFA series and SFM series. The SFA machines come with electronic controls and digital readouts while the SFM series are manually operated machines. Both also come in two different sizes, one for surfacing passenger car and light truck engines, and a larger size for heavy-duty diesel work. Rottler's surfacers use electric ball screw feeds for greater precision, and the SFA series machines feature "closed loop" electronic gearbox controls that balance the spindle rotation speed and feed rate to maintain a consistent Ra finish (as low as 2 to 3 Ra is possible).
The Rottler SF7M surfacer with manual controls, starts at $17,900 and typically sells for under $20,000 with fixturing. The top-of-the-line SF8A with automated controls sells in the mid to high $30,000 range.
The Rottler SF7A and SF8A both feature a programmable rapid touch off set point for reduced cycle times. On completion of the automatic cycle, the 14" cutter head (which holds two round or square inserts) returns to vertical zero height. The SF7A has infinitely variable spindle speeds from 350 to 1,800 rpm, and infinitely variable travel feeds of .001" to .080" per minute. The maximum work head travel distance is 40", with a rapid transverse rate of 160" per minute. The spindle is hard chromed and has large diameter triple angular contact bearings. The slideways are coated with low friction Turcite for durability. The machine also has an automatic scheduled maintenance monitor. The SF8A has all of the same features, but a larger 16" cutter head.
Though Rottler's surfacers are all designed for CBN/PCD, they have also developed some new insert materials for cutting hard blocks with high nickel content, and aluminum diesel heads with steel prechambers. Rottler also has some new inserts for resurfacing diesel heads that have been spray welded and require heavy milling.
To make setup easier, Rottler offers a leveling table as a $4,500 option. The table eliminates the time-consuming task of clamping, shimming, measuring and reclamping and reshimming a head before it can be resurfaced. Once the head is clamped to the table, two handles allow the table to be quickly and easily leveled in any of four directions using a touch-off dial indicator on the cutter head shroud.
Peterson Machine Tool has just signed a marketing agreement with T & S Machine to sell the T & S Block Mate surfacing machine. The Block Mate is a high speed surfacing machine that keeps evolving and includes many features that make it one of the easiest and fastest machines on the market. The machine has a universal cradle that works on almost anything and is very fast to set up thanks to the built-in dial indicator. The Block Mate can convert from heads to blocks in less than a minute, and can angle mill a pair of V8 heads in less than 30 minutes. It is the only machine currently on the market that uses a sliding indicator to align the work piece. It is a single-pass machine that uses a single CBN insert for milling cast iron or aluminum (PCD can also be used for milling aluminum). The Block Mate can handle heads and blocks up to 37" long and 10" wide, and is rigid enough to take cuts as deep as .030" at feedrates of up to 60" per minute in either direction. It can also be converted in less than a minute into a boring machine. Block Mate takes up less floor space than many other surfacers with a footprint of only 66" by 36". The price is just under $20,000.
Peterson also sells a Model 900MVA surfacer, with a base price of $12,995 that includes a ball screw driven table with variable transverse speed, auto lift and retract system, push button operation and automatic return. The machine can handle heads up to 35" in length and blocks up to 18-1/2" high. The machine has a 14" cutter head for CBN/PCD inserts.
Winona Van Norman has changed the model number of its surfacer to SM101 to reflect its new ball screw drive table (it was formerly a rack and pinion drive). The CBN cutter head can do blocks 24" high, and head lengths of 39" (longer table travels are available).
Winona Van Norman's SM Series surfacers feature Winfield fixturing that allows fast and easy setup of work pieces, infinitely variable table traverse, a power column to help the operator finish the job fast, rugged cast iron base with precision ground and matched ways, flat and "V" way construction for accurate parallelism and side-to-side tracking, and cast iron "box" type columns with dove tail ways and precision spindle bearings for added rigidity and accuracy. The SM Series machines can also be converted for grinding. The standard CBN cutter head is 13.8" in diameter, and holds two inserts.
Winona Van Norman also has a new SM70 surfacer for motorcycle and other small engines. It's a combination milling/grinding machine that has enough capacity to also handle small block Chevy cylinder heads. The selling price is $8,595.
For diehards who prefer to resurface with carbide, Storm Vulcan sells its Classic 85 resurfacer that comes with manual controls and variable speed and feed. The cutter head holds 16 indexable carbide inserts and is capable of delivering surface finishes of 15 Ra or less. The price is $17,995 complete.