Piston clearance is an important part of cylinder boring. If the clearance is too small, it can lead to "poor lubrication" and cause seizures after the repeated operation. Conversely, if the clearance is too large, compression will be reduced and burned engine oil will blow out of the muffler as white smoke. Let's understand what the boring operations and the honing operations are like, and understand the importance of these operations in determining the condition of the engine.
Microscopic view of the inner wall of the cylinder is zigzaggy.
Cylinder inner walls are bored to the nearest 1/100th of a millimeter. After that, "honing" is performed by polishing with a special grinding stone. The dimensions to be polished during this honing vary depending on the bore size, but one side is 30 to 50/1000 mm, and the maximum diameter is about 0.1 mm. The moped class has a smaller bore, so the amount of finish grinding is even smaller. In general honing finishing, one type of grinding stone is used for the finished size. At first glance, the cylinder's inner wall appears smooth, but when checked at a microscopic level, its surface is jagged and rough. The edge side of these zigzag is the "groove" of the crosshatch, which serves as an oil reservoir and maintains lubrication.
Meaning of "Plateau Honing."
While general honing is finished with one type of grinding stone, plateau honing is performed with a hard, coarse diamond grinding stone until just before the finished dimension is reached, whereupon a special ultra-fine grinding stone is used for plateau honing to achieve the piston clearance desired by the user. The ultra-fine honing process makes the surface smooth and flat, creating a so-called plateau. This plateau area firmly receives the sliding motion of the piston, and oil accumulates in the serrated edge area and retains an oil film. Therefore, the lubricity against piston sliding is extremely high.
Strictly measured with a surface taximeter
A high-precision surface roughness meter is being used to measure the condition of the finished interior walls. The higher the number displayed on the data monitor, the greater the difference between the lowest and highest points, and by checking the jagged monitoring that appears on the measuring instrument. It is understandable that a plateau is being formed. The depth of the cross-hatch grooves is measured in microns by a surface roughness measuring instrument and graphed. Inoue Boring also attaches a printout of the graph to the cylinder delivery.
Measures roundness at various angles
As described in the factory service manual issued by the manufacturer, the inside wall of the cylinder after honing is measured for the finished dimensions in the front-back and left-right directions for the upper, middle, and lower bores, respectively. The inner walls of the cylinders after honing must have the same dimensions in each direction, or be within the allowable range for the bore size, in order to be called precisely bored. The honing engineer uses cylinder gauges to measure the finish at each step of the work process.
Point
Point 1. Boring and honing to be requested at a professional store for machining internal combustion engine parts because of the precision-machined finish.
Point 2. The engine tuner, who is the client, can determine and change the clearance values.
Point 3. By adopting plateau honing, it is possible to complete the warming-up operation in an extremely short time.
In general, honing finishing is a process in which the inner wall of the cylinder, which has been bored out, is polished with a special grinding stone to the specified dimensions while leaving a machining groove called a "cross hatch". Specifically, if the piston clearance is set at 5/100 mm, stop the cutting operation using the boring tool (cutting tool) before the finishing dimension and polish the inner wall with a honing-specific grinding stone to finish the inside diameter 5/100 mm larger than the piston outer diameter dimension. This dimensional difference is called "piston clearance". Scratches on the inner wall of the cylinder during the honing process are called "cross hatches," and these grooves act as oil reservoirs to lubricate the piston and prevent it from seizing.
The process of machining the inner wall of the cylinder by gradually enlarging it is called "boring." After boring is completed, the inner wall of the cylinder is polished and finished with a special grinding wheel, which is called "honing". In other words, it is important to know that the process is not completed by either of these operations alone, but rather each operation is completed as a set. In general, internal combustion engine machining is often referred to collectively as "boring" when repairing a reconditioned oversize piston.
In general honing, cross-hatching of the same depth is applied to the entire cylinder, but in a technique called plateau honing, a "plateau" is formed on the cylinder's inner wall, and an oil reservoir is created at the plateau, and a deep cross-hatch (edge). This changes the cylinder's inner wall that slides against the piston skirt from a line to a broad surface, and a strong oil film is formed on that surface so that the piston and cylinder fit together so drastically that a warming-up operation is no longer necessary immediately after assembly. This plateau honing process utilizes a coarse, hard diamond wheel in the initial finishing stage to create deep cross-hatch grooves on the cylinder's inner wall. The sharp edges from rough finishing are then polished off with an ultra-fine grindstone to create a plateau, which is then finished to the specified piston clearance.
Inoue Boring, which provided cooperation for the photo shoot, has many years of experience in manufacturing and delivering "genuine manufacturer's repair parts" in the past, and has a track record of being one of the first to adopt this precision boring finish.