.
Boring out cylinders to accept oversized pistons or sleeves has long been a common practice in the engine rebuilding business. Boring allows worn blocks to be salvaged, and stock cylinder bores to be enlarged for more displacement. More recently, boring is also being used to install special cylinder liners with hard surface treatments in high performance racing engines. The hard liners almost eliminate ring and bore wear so the engine can run race after race with no increase in bore clearances blowby.
Like most other machine tools in today's shops, the equipment used to bore engines is also evolving to keep pace with changes in engine technology and the aftermarket. Small shops want equipment that is versatile and can do more than just bore holes. For this end of the market, combination boring/milling machines have become popular. At the other end of the spectrum, production engine remanufacturers (PERs) want equipment that works harder, works faster and requires less operator input. For this type of user, automated high speed boring equipment provides the needed boost in productivity and quality.
Tooling has also been improving. The latest generation of coated carbide inserts provides longer life and better cutting action. For high speed boring, polycrystaline diamond (PCD) provides the longevity needed for this type of operation.
Entry Level Access
For someone who is just getting started, a
basic boring bar and fixturing are the cost of admission. John Stratton of
Kwik-Way says his company has been manufacturing boring bars since 1932
and has been selling the same basic boring bar for decades.
"Our portable boring equipment is a viable alternative for shops that cannot afford to spend $25,000 to $50,000 or more on a boring system. The basic boring bars we sell are fast and accurate, and offer small shops a way to get into the boring business at an economical price.
"The bar itself is about $8,500, and we have a $3,400 stand you can put the bar on as an option. If you add an airfloat, the total cost is about $12,000. With this setup, you can bore a Chevy smallblock V8 floor-to-floor in about 22 minutes. The only thing our equipment cannot handle are the big over-the-road diesel blocks."
Stratton says that Kwik-Way introduced a new "micro grain" carbide bit three or four years ago that works well on the harder blocks. "We have a lot of customers who have upgraded to our new carbide bit because they can bore a lot more holes between sharpenings."
Stratton says one thing shop owners must have if they are going to bore engines today is some type of holding fixture or boring stand. Mounting the bar on the decks of newer engines with thin wall blocks is not a good idea because it can create distortion in the bores. The boring equipment will cut a round hole, but when the bar is unclamped from the block the bore may shift causing the hole to go out-of-round.
"Torque plates can reduce bore distortion, but most smaller shops are not using them for boring. They will leave .003˝ to .005˝ in the bores for honing, and then use a torque plate when they are honing," says Stratton.
Ed Kiebler of Winona Van Norman says his company is introducing a new product that is relatively inexpensive compared to many boring systems. "If there is one trend today, it is that everything keeps getting more and more expensive. So what we have tried to do is bring to market a complete system for just under $15,000.
"Our new CB2500 has the same stand but a reengineered bar. We have gone to a bigger spindle, changed the way the fingers come out of the bar and made other internal changes. The bar now goes from 2.6 up to 5.2 inches, and can do small engines, passenger car and light truck engines, but not big diesel engines. It is designed for the smaller customers who cannot afford to spend $25,000 or more on a boring machine but who need the capability to bore blocks."
Kiebler says he does not think torque plates are as necessary as they once were for boring or honing. "Most of the new engines have torque-to-yield head bolts that are 10 to 13 inches long. The bolts thread into the main bearing webs so you do not get the cylinder distortion that you used to. So on these engines, torque plates are probably less necessary than they were on the older blocks," says Kiebler.
The Cutting Edge
Peterson Machine Tool says the biggest change
that has occurred in recent years with boring equipment concerns the tool
bits and holders. The materials are better and tooling life is longer, but
prices are also more competitive. It says the standard carbide bit will
probably do about 40 to 50 holes per corner for normal boring. The
modified carbides will do more. But many of the bits have six or eight
sides, so the tooling cost per hole is "pretty minuscule," it
explains.
The changes in tooling have had the biggest impact with PERs because they bore so many holes on a daily basis. It has had less of an effect on the smaller shops because for them tool longevity is not that big of a deal," says Peterson.
Peterson says you can do a better job boring with a brazed-in bit because it gives you better control. But it is difficult to sell brazed tools because the average shop does not want to take the time to sharpen them. It�s easier to use an insert and just turn a corner when it becomes dull, the company says.
Peterson says the speed at which the boring bar turns has a significant impact on tooling life. High speeds just kill the bits unless you use a PCD or cubic boron nitride (CBN) type of insert. The high speed boring machines that go up to 1,500 rpm need these type of inserts.
As the boring speed increases, the metal tends to fracture more than it cuts. This can leave a rougher surface that requires additional honing to get down to base metal. At high speed, Peterson says the cutting action is more like breaking wood than cutting it with a knife. This leaves a lot of fractured debris on the surface which has to be removed by honing."
Peterson says the best boring job can be done at 400 rpm with carbide tooling, and requires only .003˝ to .004˝ of honing to finish the cylinders.
Different Markets
You can start out with a new boring bar for $4,000, which Peterson sells in three different sizes. You can add a stand for less than $1,000 up to $4,000 depending on the configuration. An airflow boring bar will cost in the mid-$20,000 range, and a combination boring/milling machine in the low $30,000 range.
Although portable bars have been the standard for years, Peterson says one of the challenges with using them is attaching the bar to the block, particularly on engines with small deck surfaces. That is why boring stands have become popular. Peterson sells four different boring stands which eliminate the mounting problem.
A lot of small shops like the combination machines because it allows them to bore, counterbore, sleeve and resurface without moving the block once it is mounted in the fixture. The trick here is mounting the block so the cylinders are at a right angle to the boring bar. This can be a challenge if the engine has nontraditional angles like the Volkswagen Passat V4 that has a 15 degree spread between the cylinder banks," Peterson explains.
Peterson also sells a lot of portable bars that can handle everything from a small 50cc Honda engine up to a passenger car V8. Its boring systems with CNC controls that go from hole-to-hole and bore automatically are also selling well to engine builders.
Peterson says most PERs use high speed automated equipment for boring, and that few are using diamond rough honing to oversize cylinders. It is cheaper to bore and then hone than to try and do it all with hones.
One of the limitations of honing is the amount of overstroke you can do at the bottom of the hole. Many engines do not allow much more than 1/4 to 1/2 inch of overstroke. So if honing is used instead of boring, you can end up with a crooked hole and no way to correct it.
Boring is only half the picture. Honing is the other half. There is good money to be made boring and honing, but you must have the right equipment and tooling to do it.
PERs and Performance
Ray Meyer of RMC Rogers Machine Company
says new CBN tooling that has entered the market in the past couple of
years has set a new benchmark for cycling times. "With CBN and high speed
boring equipment, you can now bore a cylinder in 30 to 40 seconds at 1,200
to 2,500 rpm. This is the kind of speed it takes to meet the needs of
today's production engine rebuilders."
Meyer says RMC has recently introduced a new high-end machine geared to the needs of PERs. The RMC-V40 is a fully automated, CNC-controlled engine machining center that inspects the block and automatically determines the bore size and amount of machining needed to restore the block. It then picks the correct tooling, bores the block and decks it, too. Meyer says the floor-to-floor cycle time is only eight minutes with a V6 engine.
"This machine does everything. It uses a probe to check the block's position on the fixture, measures bore tolerances and automatically lines up the holes and bores them. There is no other boring machine as automated as this one. I think it will revolutionize the way PERs bore and deck engines."
The RMC-V40 sells for $79,000 to $120,000 depending on the number of boring heads and tooling.
Meyer says he sees a coming "onslaught" of manual boring machines entering the market. "These are dead mills that have been converted for automotive work. The base machines sell for about $30,000 and go up to $45,000 fully tooled. These machines can inspect, bore and deck but with manual controls. The most likely customers will be performance engine builders who will use them for blueprinting."
Meyer says he also sees more multi-purpose machines coming, ones that can be used for boring, milling and even head work. The machines might not be fast, but they will be well-suited for small shop owners who can�t afford to buy three or four dedicated machines for each different operation they do.
The Import Market
One of the hottest markets right now is the
import market according to Anthony Usher at Rottler Manufacturing in Kent,
WA. "A lot of import engines are being resleeved, so we have introduced a
new F3 machine for this market. The F3 is perfectly suited for import
engines and sells for $22,000 up to $48,000 depending on how it is
equipped."
Usher says performance engine builders who are building turbocharged Honda street engines are boring out the aluminum blocks and installing special liners to beef up the blocks.
"We will be helping the AERA Vanguard committee with an import aluminum project engine that will be featured in Engine Builder magazine," Usher explains. "The completed engine will be auctioned off at the AERA Show in April."
Boring out these engines requires multiple cuts. One feature in the F3 machine that Usher says makes the job easier is a programmable depth control. Once a depth has been entered, the machine will bore it to the same exact depth every time.
Another problem with boring aluminum is that it sticks to carbide bits. This requires using a lot of lubricant to keep the chips from sticking. "We use PCD tooling with our bar for these applications because aluminum won't stick to PCD. It is the same material we use in our surfacing machines because it cuts cleanly and requires no lubrication. PCD also gives a really smooth bore finish, which improves heat transfer when a sleeve is installed."
Usher believes more boring and sleeving will be seen as time goes on. "The old Chevy and Ford iron V8s are being replaced with new aluminum engines. One example is General Motor's LS1 engine. It is an aluminum block with iron liners. Some shops are boring out the old liners and installing bigger sleeves to increase engine displacement. But when you bore through the old iron liner and hit the aluminum, the aluminum adheres to the carbide. So at that point, you need to switch the tooling to PCD to finish boring the aluminum to size," says Usher.
Looking at the products available now and projecting what will be coming down the pike indicates that the future of boring will be anything but "old hat."
More Engine Related Articles:
Click Here to See More Carley Automotive Technical Articles
