A crankshaft is essentially the part of an engine which is used to convert circular motion of the piston into rotary motion. In simpler words, it converts up and down motion into whirring motion. The word comes from “crank” and “shaft”. The shaft will have a crank on it, which turns typically by a belt running from the pulley above.
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Basic Specifications of a Crankshaft
A crankshaft is a connecting rod that connects the piston to the cylinder. For an engine to run, the crankshaft has to move in one direction (from left to right). This motion is called rotation.
- The key part of the crankshaft is the crank pin. The crankpin is a metal shaft with two ends a flat end and a round end. The flat end fits into the hole in the connecting rod while the round end sits in the round hole on the bottom of the piston.
- The piston pushes down against a ring in the combustion chamber and lifts up like a hand pushing down on a clock’s second hand to turn over the engine.
- A pair of crankshaft pulleys (a pulley is a wheel that uses gears) drives each half of this motion. These are called countershafts because they spin on their own axis just like gears do when you spin them with your hands.
- The two pulleys are connected together via another gear and then another set of countershafts connected to each other by yet another gear.
- The final piece is belt or chain, which drives all of these pieces from big pulley found on top of crankshaft through each countershaft.
Remove and disassemble the crankshaft
- Remove the flywheel and loosen the engine. Some engines can be released from the gearbox through a special fixture. The most common method of removing the crankshaft, especially with older motorcycles, is to remove the entire engine and place it on a special stand.
- Disassemble the crankshaft and remove all parts not related to grinding. This includes removing flywheels, connecting rods, pistons and bearings. When disassembling the crankshaft, it is necessary to carefully mark all parts so that they can be returned to their original positions when reassembling. After disassembly, remove all dirt from the crankcase using kerosene or other solvent.
Check for cracks
- Check the crankshaft for cracks. The easiest way is to magnaflux the crankshaft. Magnafluxing will show any cracks in the crankshaft that may not be visible to the naked eye. This can be done at a machine shop and is relatively inexpensive.
- Clean the crank. Next, clean all of the parts of your crankshaft with a wire brush and degreaser cleaner. Clean all of the grooves and nooks of each part of the crank with an air compressor and blow gun. All parts need to be free from rust, dirt or grease.
- Remove all bearings from the crankcase and inspect them for wear or damage. The bearing numbers should be on the side of each bearing so you know where they go back on during reassembly.
- Inspect all connecting rods for damage or distortion. If any are bent, have them checked out by a professional mechanic before reassembly as these can be dangerous when in use if not properly fitted to their original position on the crankshaft.
Measure parts
Measure the crankshaft with a micrometer. This tool measures thousands of an inch and is used to measure the crankshaft to ensure its within factory specifications. If it’s out of tolerance, you’ll need to grind the crankshaft down to size before you can proceed.
Set up your equipment
You will need a large work space, a grinder, a cleaning bucket, and clean rags or cloths. When it comes time to do the actual grinding work on the crankshaft, you will also need your grinding stones, either vitrified or resin-bonded, depending on what type of stone you prefer. It’s also helpful to have a balancing machine on hand as well as dial indicators for checking runout measurements.
Grind the crankshaft
Grinding a crankshaft is a process of removing material from the journals in an effort to refurbish and reuse an expensive, yet vital component of an engine. It is usually done during the process of rebuilding an engine when needed, but also has some performance aspects which come along with the process.
There are numerous kits specific to grinding a crankshaft that can be purchased off-the-shelf at your local auto parts store. The kits consist of various grades of sandpaper belts ranging from coarse to fine, so that you can use a “roughing” pass followed by a “finishing” pass.
Assemble the crankshaft, bearings, and caps
Before starting work on processing a crankshaft, it is recommended to study several drawings that show its assembly and disassembly process in detail. First you should assemble all parts into one unitThe crankcase consists of a block and a head, which are made from cast iron or aluminum alloy depending on the production technology and the manufacturer’s preferences.
The main important part of the engine is the crankshaft, which transmits energy from moving pistons to rotating gears. It is he who must be processed if there is a need for major repairs in order to restore its original parameters. This operation is called grinding, and it consists in removing a thin layer from the cylinder shaft surface with abrasive powder using special equipment – a tool grinder.
Conclusion
Grinding a crankshaft at home can be done with careful attention to safety and precision. A crankshaft grinding jig makes it easy to keep the crank at a fixed angle while grinding. For example, a jig can hold the crank at twenty-five degrees while you rotate the crank during the grinding process. A tool rest may need to be built to support one end of your stone.