The market for crankshaft grinding has changed a great deal in recent years. With many passenger car and light truck engines now lasting upward of 200,000 miles, there’s much less demand for grinding crankshafts than there used to be. By the time the engine needs major work, the vehicle has often depreciated to the point where spending a lot of money overhauling the engine simply isn’t worth it. Or, if the vehicle owner does want to fix the engine, it is often cheaper to replace his old engine with a new or remanufactured crate engine.
Another factor that has contributed to the demise of crankshaft grinding is the popularity and affordability of crankshaft kits. Why bother refinishing the old crank when it can be replaced with a reconditioned crank and a new set of bearings? Many times, the old crank can’t be reused anyway because it is cracked, damaged or worn beyond limits.
The influx of low-cost prefinished crankshafts from offshore suppliers
has had a big impact on the domestic crankshaft market and crank
grinding business. So the idea of engine builders or machine shops
actually doing crank work is just laughable, right? Maybe not.
While it’s true that imported cranks have had a significant price advantage over domestically-produced crankshafts, that may be changing. Rising fuel costs are now making it much more expensive to ship products halfway around the world. The price to ship a container of crankshafts has gone up 800% in the last year! Consequently, the import price advantage is narrowing – and is actually going away in some cases.
Stroker cranks are a popular substitute for stock cranks when small block Chevy and Ford engines are rebuilt. The same is also true for big block Chevys. So there is still a need for crankshaft grinding in many performance shops that do custom engine work and don’t just assemble prefinished parts right out of the box.
Though much of the crankshaft grinding business has disappeared from the passenger car and light truck markets, it remains strong in the heavy-duty diesel truck, industrial engine and marine engine markets. Because these are high dollar motors with a lot of intrinsic value, when one of these big engines breaks down, it is usually worth the money to overhaul it and return it to service.
Grinding the big crankshafts in these engines obviously takes a larger machine than one designed for smaller passenger car and light truck crankshafts. Some of the larger crank grinders can handle cranks ranging from 72? up to 100? or more in length – which also opens up the possibility to broaden your customer base and grind other large rotating parts, not just crankshafts.
New Crankshaft Grinding Equipment
Though some would say the basics of crankshaft grinding probably haven’t changed much in the past 50 years, and that the basic design and operation of a crankshaft grinder has remained pretty much the same in recent times, there have been some significant changes.
The most notable change has been the introduction of high-end CNC (computer controlled numeric) crankshaft machining centers. Some of these machines can cost up to $1 million, so they are obviously way out of reach for all but the largest production engine rebuilders or a handful of big name performance engine builders. But for those who can afford them, they can revolutionize the way cranks are ground. And CNC equipment is becoming more and more accessible every day.
Everybody who has a conventional crank grinder in his or her shop knows how labor-intensive crank grinding can be. The operator really has to keep on top of the job to make sure each journal is finished correctly. He has to keep the grinding wheel dressed, he has to make sure the journals are cut to precise tolerances, and he has to make sure the radius in the journal fillets is correct. It’s a job that requires a high level of skill, experience and the ability to stay focused. It’s not for everyone, that’s for sure. And it’s hard to find qualified people who can operate a crankshaft grinder. That’s where CNC can make a big difference.
With a CNC machine, the entire process is run automatically. Once the operator sets up the equipment and mounts the crankshaft on the machine, he can press a button and walk away. Consequently, it takes much less training to learn how to set up the machine, and much less skill and experience. The automatic process controls allow the operator to walk away and do something else while the crank is grinding. Then five to eight minutes later, the finished crank can come off the machine and be replaced with another to keep the process going.
CNC works equally well with both long production runs and one-of-a-kind jobs. Once the basic parameters for a given crankshaft have been entered, the data can be stored for future jobs.
Lyle Haley said Berco has introduced a new CNC crankshaft grinder called the “Lynx” that can handle both smaller cranks and larger ones. The fully automated machine is unique in that it can grind both the main journals and rod journals in one sequence, and it automatically dresses the grinding wheel. It can also grind camshafts as well as crankshafts, eliminating the need for two separate machines. It can also use a CBN (Cubic Boron Nitride) grinding wheel that runs at twice the speed of a regular grinding wheel. A water-based synthetic coolant is used to minimize maintenance.
“This machine uses no traditional motors or ball screws. It uses magnets to drive the table, making it much faster and more accurate than a traditional crank grinder. That’s why Ferrari uses this machine to grind their Formula One racing cams in Italy,” said Haley.
CRANKSHAFT GRINDING TIPS (Courtesy of Goodson)
• Before mounting a grinding wheel on a crankshaft grinding machine, inspect it for cracks or damage. This can be done visually or by giving the wheel a “Ring Test.” A good vitrified wheel with no cracks will give a clear ringing tone when tapped with a wooden or plastic mallet. A cracked wheel gives off a dull sound which is quite different.
• Every wheel is marked with its maximum operating speed in rpm. This rating must be checked against the actual rpm of the spindle which will drive the wheel. The spindle speed should be checked from time to time with a tachometer to be sure nothing has changed.
• Most on-machine grinding wheel breakage is caused by incorrect mounting. Pay special attention to the condition of the flanges. They must be flat and of equal diameter plus have full contact with the sides of the wheel. The flanges must also be relieved so that they do not contact the grinding wheel in the area of the arbor hole.
• Use a new blotter every time the wheel is mounted. The blotters are made of compressible paper which takes up any high points on the side of the grinding wheel. Direct contact between the flange and the side of the wheel could cause a stress point where a crack could begin.
• In order to achieve the best results from your grinder, every grinding wheel installed on the machine must be balanced. Rebalancing wheels is a good habit to get into and balance should be checked each time a wheel is reinstalled on the machine.
• Do not allow grinding coolant to run on the grinding wheel when it isn’t rotating. This will cause the wheel to become saturated with coolant on one side and the wheel will be thrown out of balance. This condition can be corrected by turning off the coolant and running the wheel until all the coolant has been removed.
• Manual dressing of the grinding wheel is another important factor in producing satisfactory work on your crankshaft grinder. The wheel must be dressed each time it is placed on the machine, even though it may not have been removed from the wheel center. Mount the wheel dresser on the grinder table. Bring the rotating grinding wheel up close to the diamond and start the coolant flow. Never dress without coolant! Frictional heat buildup can cause the diamond to come loose or separate from its mount. Lack of lubricating properties (along with cooling) abrades diamond needlessly.
Best results will be obtained if the diamond is brought into contact with the center of the wheel, feed in a maximum of .002? then traversed each direction (left and right) off the edge of the wheel. Learning the best traverse rate for dressing the wheel is a matter of trial and error for each operator. You have to be fast enough to prevent glazing, but slow enough to minimize spiral lead marks. Dressing from the center of the wheel outward to each edge helps minimize the effect of the spiral lead marks on the finish of the workpiece. Do not remove over .002? per pass. Excessive in-feed will cause the wheel to act like it’s loaded. This results from wheel material being “pasted” into new exposed wheel porosity.
• When regrinding a crankshaft, every attempt should be made to duplicate the original corner radii to prevent the crankshaft from being weakened. Position the diamond in the holder facing out the front. Slide the holder back, position and lock the radius adjuster at the desired dimension. Then slide the diamond holder forward until the diamond contacts the radius adjustment stop. Tighten the diamond holder, unlock and retract the adjustment stop.
Feed the wheel into position fully forward. Using fine feed, bring the diamond into contact with the front face of the wheel and dress full width. Then back the wheel away from the diamond .004?; loosen the swivel lock and remove one of the stop pins so the upper swivel can be rotated though 90 degrees of travel. While pivoting the diamond through its 90 degree arc, bring the wheel into contact and dress off the required amount from one corner. Repeat this process for the opposite corner by replacing the first stop pin and removing the second pin to provide 90 degrees of rotation in the opposite direction.
Be sure to keep your diamond dresser tools sharp. Rotate the diamond 30-45 degrees after each dressing operation.
Crankshaft Grinding and Polishing Equipment
If you’re looking for a good used crankshaft grinder, there are a bunch of them for sale. As smaller shops have gone out of business, other shops have been able to pick up good used equipment at bargain prices. Even so, no piece of shop equipment lasts forever. Eventually, it wears out and may be to be rebuilt or replaced. Dan Cavalieri of Peterson Machine Tool said his company no longer sells crankshaft grinders, but that they are rebuilding some used crank grinders for customers.
“We have seen a major change in the crankshaft re-grinding and repair market,” Cavalieri says. “As the cost of re-grinding can be close to the cost of a replacement crankshaft, machine shops have changed the way they market complete engine rebuilds.”
Cavalieri says in many cases used crankshafts need nothing more than the finish to be restored by polishing. Many shops find that doing this operation on a lathe or on the crankshaft grinder itself leads to a situation of debris contaminating the machine, which requires extensive clean up to remove the grit and debris. Dedicating a machine for the polishing operation allows the shop owner to control the contamination. There has also been a decline of shops that offer crankshaft grinding, forcing some shops into doing some crankshaft re-work in house.
“We have updated our product line to include the CPM-60A Crankshaft Polishing Machine and the CPM-60 Crankshaft Polishing Unit. The CPM-60A is a complete, heavy-duty crankshaft polishing unit that incorporates an adjustable height tailstock/rest. This design allows for easy loading and unloading and can accommodate crankshafts of up to 60?. The polishing unit itself is mounted on the rear on the machine, and incorporates a linear guide rail and bearing for ease of positioning the polisher. The polisher itself is made with a quick belt change feature that allows the operator to change belts in seconds with no tools required. The CPM-60 incorporates the main machine structure and features of the CPM-60A, but is designed to rotate the crankshafts while the operator performs the polishing with a hand held, portable polishing unit. As many shops are now polishing their own shafts with a portable polisher, the CPM-60 allows the shops to use their existing portable polisher without the fear of prematurely wearing out existing equipment with grit and debris generated by polishing,” said Cavalieri.
“We feel the trend of new aftermarket crankshaft replacement will continue for most popular engine families. We have seen that some of these cranks can benefit from a final polish before they go to the end user,” explained Cavalieri.
“Another trend we have seen is the increase in the sale of airless shot blasting equipment for use in crankshaft repair and grinding. For those shops that continue to re-grind crankshafts, this machine is a must. When a crankshaft is brought in for rework, the airless blaster can take a rusty work-piece and transform it into a bright casting that looks like it was newly manufactured. The beauty of this machine is that it is versatile and can be used for a wide variety of cleaning needs in the shop.
Some shops will use the airless blaster for stress relieving the crankshaft and rods after re-grinding and reconditioning. Peterson currently manufactures two sizes of Airless Shot Blasters and with the ability of our sister company Viking Blast & Wash Systems, we now offer an extensive line of blast cleaning equipment,” Cavalieri said.
Perterson’s spokesman says that in the last few years, the company has tried to accommodate many crankshaft repair shops who have asked them to construct a spray washer for their unique cleaning needs. Peterson has created several new models of spray washers to accommodate the height issues without the larger diameters that at times are not needed. The company has taken its standard 28? diameter machine and taken it from a 42? to a 50? and now to a 62? height. Peterson also has the capability to customize equipment to tailor fit the end users particular needs.
“Another trend we have seen the last few years is in the increasing sales of non destructive particle inspection equipment used for crankshaft inspection,” said Cavalieri. “We now offer two types of machines, primarily because some shops were becoming reluctant to use an oil-base carrier for their particle inspection. These shops tried to use the water based product and discovered that their current machines were suffering form rust and cancer. With this problem we created this machine that is built with a stainless steel tank and sized for automotive crankshafts.”
Joe Baker Sr. of Baker Equipment Sales said his company sells Berco crank grinders, and that the prices can range from $114,000 up to $147,000 or more depending on the machine and what comes with it. Like the other equipment suppliers, Baker said the market has definitely shifted toward the bigger diesel engines these days. “The small stuff (passenger car & light truck) is about done,” he lamented.
Ray Meyer at RMC Engine Rebuilding Equipment said he’s not seeing much demand for new crankshaft grinding equipment these days, except for the larger machines that can handle the big diesel cranks. But he has seen an increase in demand for crankshaft and camshaft polishing equipment. “A camshaft polisher works similar to a crankshaft polisher, but it takes a different arm with an idler wheel to follow the cam lobe properly,” he said.
“Our crankshaft grinders sell for $80,000 to $90,000, which includes gauging and a crankshaft straightener. You also need a magnetic particle unit for crack detection, which adds about $5,000 to the price,” said Meyer.
Terry Wagner of Storm Vulcan said his company is selling more crankshaft grinding machines for the big diesel, industrial and marine engines these days, some with crankshafts as long as 178 inches. Storm Vulcan also has a basic crankshaft grinder (manual, no hydraulics) that sells for around $60,000.
Wagner said he is also seeing a demand for polishing equipment, which he attributes to the use of more billet and forged steel crankshafts today. “Many of these cranks require a smoother journal finish in the 4 to 6 Ra microinch range,” he said.
Britton Harper with Winona Van Norman said his company is now offering some grinding equipment with more automated controls. “We have a CNC crank grinder that can also do camshafts, and we still have our manual and hydraulic crank grinds which continue to appeal to the smaller shops.”
David Monyhan at Goodson Tools and Supplies said his company’s PCP1072 crankshaft polisher, which is a 72? hand-held polisher, has been doing well, and they’ve just introduced a new series of “Ruby” premium belts for it in 600 to 800 grit sizes for super-smooth finishes. Most polishing belts are 240, 300 or 400 grit sizes, so the Ruby belts can be used to take the finish down even smoother.
“We also offer one of the most complete selections of grinding stones that are available to engine builders,” said Monyhan. “Goodson buys grinding wheels in bulk and trims the wheels to any diameter or arbor size to suit our customer’s needs.” Grinding stones are offered in three grades: “Standard” for cranks that have a hardness of less than 35 Rc; “Superior” for nodular iron and forged steel cranks that are less than 35 Rc; and “Premium” for diesel, billet and top fuel dragster cranks that are harder than 35 Rc.
Goodson also offers camshaft grinding wheels in two grades: GCC for standard cast iron camshafts, and a #70 grit green silicon carbide for hardened steel diesel and performance camshafts.
“It is important to select the proper grinding wheel for the intended application,” said Monyhan. “One wheel cannot do everything.”
Micropolishing
Traditional polishing techniques that use a manually-operated belt sander require a fair amount of operator skill and experience to achieve a journal finish that not only looks good but also has the proper surface finish in microinches and is dimensionally correct. If the amount of pressure exerted by the belt against the journal varies significantly or the belt is held in one place too long, it may alter the geometry of the journal slightly creating some taper or out-of-roundness.
If the time spent polishing the journal varies or the entire width of the journal is not polished evenly, the surface finish can vary from area to another on the journal. Multiply these variables by the total number of journals on each crankshaft times the number of crankshafts polished in a week and it adds up to a lot of potential for error.
If the surface finish on the crankshaft journals isn’t right or the geometry is slightly off, the bearings will suffer the consequences when the crankshaft is put into service. No engine builder wants to see an engine fail under warranty because the crankshaft journals chewed up the bearings – but it happens all the time.
The alternative to manual polishing is automated micropolishing with micron abrasive tape. The micropolishing machine clamps the tape around the journal and automatically controls the polishing process, eliminating the risk of operator error.
Micropolishing equipment designed for the aftermarket is available from QPAC. Ken Barton of QPAC says his machine provides two-directional polishing and uses abrasive tape that is available in various widths and micron sizes (typically 15 to 40, with 30 microns being the most common). The machine supports the tape with a backshoe when it clamps down on the journal to assure even pressure all the way around. The time and direction of the finishing procedure is controlled to eliminate any variability from one journal to the next.
Barton said another advantage of micropolishing versus belt polishing is that journals can be polished with a single pass. Belt polishing may require multiple passes and/or belt changes. Polishing in one direction and then automatically polishing in the opposite direction also leaves a better finish and eliminates microscopic peaks that can cause premature bearing failures. The finishing process always ends in the same direction as engine rotation.
The results do not depend on the skill of the operator, nor do they tire the operator or risk arm or joint injury.
