To obtain a superior finish on a crankshaft journal, all available equipment must be used to support the journal as it is being ground. Besides the headstock and tailstock, which are used to secure the crankshaft in the grinding machine, a steady rest and its shoes are used. If you look to the image to your left, you will see the side view of a Winona Van Norman steady rest and the shoes that come into direct contact with the crankshaft. Although the Winona Van Norman model pictured to the left does not have a dial indicator, most models accept this precision measuring device as an accessory.
When grinding the rod journals, a steady rest is typically positioned to the side of the oil passage and tightened down to the grinding machine’s ways. Since the shoes ride directly on a journal, they must avoid the oil passage as a shoe may be drawn into the hole and damage the crankshaft and/or the equipment being used. Also, there must be adequate room for the operator to use the Arnold gauge to measure the amount of material being ground off. Especially on V6 crankshafts, where there is little side to side clearance, placing tooling and measuring devices on the journal at the same time can be quite a challenge. Once properly positioned, safely to the side of any oil passages and with plenty of room for the Arnold gauge, the automotive machinist then slowly tightens up the steady rest so that it supports the journal as it is being ground. As the machinist takes off more material, the arms are slowly tightened even more so that shoes remain snug to the journal throughout the entire grinding process. The steady rest is the one tool that resists the force created from the grinding wheel as it is slowly fed into the journal, which is an important function to produce finished journals of the proper size and microfinish. Continue reading
For any automotive machine shop to grind crankshafts, they need a good crankshaft grinding wheel to get the job done. The surface finish of a ground crankshaft is highly dependent on the quality of the wheel being used and whether or not it has been dressed properly. As one would suspect, to grind a variety of crankshafts a shop will need a few different types of wheels so that they may repair the many different types of crankshafts that are used by various engines.
Most automotive machine shops will have a small assortment of grinding wheels available, with varying widths, so that they may grind narrow V6 journals and wide V8 journals. For industrial crankshafts, which normally have a 1/8” radius or larger, a wheel is normally reserved specifically for these types of industrial grinding operations. You may view a typical crankshaft grinding wheel by looking to the picture at your left. Although the face of this wheel is mostly used for grinding, you will see that the sides have directional grooves. These grooves help to grind thrusts or to grind additional side to side clearance in main or rod journals that have been welded. Continue reading
When a vehicle’s engine develops a “knock,” most vehicle owners shut down the engine right away or immediately take the vehicle to a service center to be looked at by a qualified ASE certified technician. Knocks are often a sign of bearing failure and if ignored, will severely damage the crankshaft journals. In some of these cases, where the journals are so severely damaged that they are unable to be repaired by grinding, a weld is needed to perform the repair.
Crankshaft welding is a process by which new material is added to a journal or thrust. This new material is needed because there are only so many available bearings available for a crankshaft that has been ground under its original size. Common oversized bearings are available in .25mm, .50mm and .75mm metric options. Older vehicle engines, which may still use inches for size, may have bearings available that are .010”, .020” and .030”. Since one millimeter equals .0393700787 of an inch, conversion is quite simple with a little math. Regardless, even at .75mm there is only .02952 inches of material that can be taken off of a journal before bearing availability becomes a problem. Continue reading
One of the most common machining operations performed on crankshafts is grinding. By grinding the rod and main journals, the bearing surface of the crankshaft can be repaired to provide a great foundation for a rebuilt engine. Below you will learn more about the grinding process, which is detailed from an ASE certified engine machinist.
To grind a crankshaft, one obviously needs the equipment to get the job done. A crankshaft grinding machine is used for this operation, and it closely resembles the appearance of a lathe. Just like a lathe, the crankshaft grinding machine (pictured left) has chucks, a headstock, a tailstock and ways which they may be accurately positioned on. The noticeable difference between a crankshaft grinding machine and lathe is that the grinder has a large grinding wheel and the chucks may be offset to accommodate a crankshaft’s connecting rod stroke. Continue reading
When it comes to repairing a crankshaft, there is a certain sequence of processes that must be followed. Once the crankshaft has been cleaned and checked for straightness, any significant runout (bend) in the crankshaft must be corrected with a straightening process. There are two primary techniques used for straightening, which are described below.
Hydraulic Press Straightening
Many automotive machine shops use a hydraulic press (pictured left) to straighten crankshafts. This is accomplished by placing the crankshaft in v blocks and applying pressure on the crankshaft journal, on the opposite side of the bend, to essentially bend the crankshaft back into its normal position. This process can be more difficult on cast steel crankshafts as they are more likely to crack under pressure. To avoid the potential of cracking, some shops apply heat to the center main journal to help it relax so that it goes back into its natural position with less force. 4340 forged steel crankshafts, for example, are less likely to break when using a hydraulic press to correct the bend since this type of steel is much softer than cast steel. Continue reading
Although most mechanics and automotive machinists understand what the individual areas of a crankshaft are called, most vehicle owners do not. Because of this, it is important for those seeking repair services to learn the terminology used by automotive professionals and gain the ability to identify these terms with the areas on their crankshaft.
In the diagrams below you will find coded arrows that point to specific areas on the crankshaft. The arrows are identified by industry standard terminology used to describe the area being viewed. A brief but concise description of what this area is responsible for is available below the crankshaft diagrams. Continue reading
Before a repair quote can be provided to the customer, an inspection of the crankshaft must be made by both a visual examination and with precision measuring instruments. Before this can occur, the crankshaft must be cleaned. Different automotive machine shops use different cleaning techniques, but baking and blasting the crankshaft is a modern process that allows more details to be seen during a visual inspection. Other cleaning processes involve the use of a degreaser machine or acid dip tank. Because of EPA requirements involving the use of hazardous chemicals are quite strict, more shops are using an automotive bake oven (pictured above) and blast process to clean crankshafts.
With a clean crankshaft, the engine machinist is able to perform an inspection that is both thorough and accurate. At this stage a micrometer is used to determine how far out of tolerance the main and rod journals are. The thrust surface is also measured with a snap gauge and micrometer to determine how much excessive endplay may be present. Providing the crankshaft journals and thrust have available undersize bearings available, or excessive damage can be repaired with a weld, the machinist will then inspect the crankshaft snout, seal surface and rear flange for damage. Continue reading