How to Install the Piston Rings when Assembling the Engine?

Pk01.jpg How to

When disassembling and reassembling an engine, or when assembling a bore up kit that allows you to easily increase the power of your engine, you need to be sure and careful when inserting the piston into the cylinder. During this process, the piston rings are compressed and inserted into the cylinder sleeve, and there are many things to keep in mind. In this section, I will report on the various "things to watch out for" related to piston rings.

Pistons are a source of energy

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The piston is where the piston rings will be installed. If the piston is a new part, apply water-resistant paper to the front and rear edges of the piston skirt and lightly scrape the corners to remove the chamfer. The paper should be 800-1000 grit, sprayed with an anti-corrosion penetrating spray, and slightly chamfered by sliding the paper over the piston edge. When using an oil stone, apply the oil stone evenly over the entire surface, rather than concentrating on one area. Be sure to apply an anti-corrosive penetrating spray at the same time. When restoring and reusing used pistons, it is not always easy to decide what to do, but there are different ways to deal with different situations.

There's a lot of theories out there, but let's stick to the basics.

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Piston ring for 4 stroke engine consists of top ring, second ring, and oil ring. The oil ring is used to scrape off the engine oil from the inner wall of the cylinder, and if the engine is divided into three parts by the upper and lower rails and the expander spring (most of the modern engines are of this type), the set angle should be as shown in the illustration. In the case of the cast iron oil ring, the angle of the top, second, and oil ring should be set at 120-degree intervals. There is no need to worry about the angle of the piston pin. This is because the piston rings of a 4-stroke engine rotate during engine operation.

The other side of the oil ring rail!

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There is a mark on the front (upper) side of the ring near where the top ring and second ring meet. For example, R(Riken), T(Teikoku), N(Nippi), 25(025OS), 50(050OS) which means bore size and so on. On the other hand, the upper and lower rails of the oil ring are not marked, but some famous tuners seem to know how to set the rails so that the side where the rails meet is inside the expander, that is, the upper rail has the downward projection and the lower rail has the upward projection. In other words, set the upper rail with the downward projection and the lower rail with the upward projection.

Be careful with piston pin clips.

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Regardless of whether it is a genuine manufacturer's part or a tuning manufacturer's part, be sure to stare at the piston pin clip before installation. There is often a burr on the cut end of the clip. These burrs must be polished off with an oil stone or water-resistant sandpaper on the back plate. Since the piston pin rotates during engine operation, the burr may affect the clip and make it easy to be removed. Both ends of the clip should be smoothed before assembly.

Performed operability check with a temporary set

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After checking the direction of the piston rings and setting them in the ring grooves, it is best to check that each ring rotates smoothly in the ring grooves before assembly. When you check the rotation, be sure to apply the anti-corrosion penetrating spray to the ring groove. In the old assembly manual, there was a description to lightly chamfer the edge of the ring joint with oil stone. This is because the edge of the joint gets caught in the ring groove, and if the ring does not rotate smoothly, it will wear out faster.

Liquid gasket is applied by rubbing it in.

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With so much attention being paid to the piston rings and piston pins, it is easy to forget about the cylinder base gasket. The cylinder base gasket can be attached to the stud bolt before the piston is assembled, or it can be attached to the base of the cylinder. To prevent oil leakage and to make the gasket come off smoothly when disassembling later, silicon liquid gasket is applied. To apply the liquid gasket, take the gasket between your fingertips, hold the gasket between your thumb and forefinger, and rub the liquid gasket into the gasket.

Best to use easy-to-use tools

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We often use a plastic band piston ring compressor when installing pistons for small displacement models with bore sizes around 40-55mm. It's simple and easy to use. When I can't find a piston ring compressor in a size that's easy to use, I cut up an aluminum juice or tea can with scissors and combine it with a hose and tie wrap to make my own piston ring compressor.

POINT
  • Point 1・ When incorporating piston rings, make the front and back sides clear.
  • Point 2・Also check the smooth operation of the ring and ring groove.
  • Point 3・Set the angle of meeting at 120 degrees and pay attention to the position of the oil ring rail.
  • Point 4・Let's remove the burr from the piston pin clip edge!
  • Point 5・The best piston ring compressor is one that is simple and easy to use and can be made by yourself.

The best way to experience the increased torque and power is to increase the bore. For example, if you take a 50cc Honda Monkey, Dax, or Super Cub and bore it up to a 75cc or 88cc engine (many constructors offer bore up kits), you will be amazed at the great driving experience you get, and you will be hooked on engine tuning from that day on. Since that day, many 4-stroke Mini fans have been hooked on engine tuning. During the bore-up process, as well as during normal maintenance, the parts surrounding the pistons require special attention. Although the parts are simple, each part has an important role to play, and if they don't play their role, the engine will not be able to perform as it should. In this section, I will report on some of the important points to keep in mind when installing pistons and piston rings.

Part 1: Piston body
Make sure the front and rear edges of the piston skirt are chamfered and that the piston pin can be inserted and removed smoothly. Let's check. Pistons that have been removed for overhaul often have burrs in the clip groove when the pin clip is removed. If you insert the piston pin in such a condition, you will feel stiffness or reluctance. While visually checking the removed piston pin and clip, try inserting a single-piston pin into the pin hole. If the pin is inserted smoothly, there is no problem, but if it does not go in easily, do not force it in. Instead, use a scraper or a stuck oil stone to polish off any burrs on the pin hole edge or clip groove. Be sure to spray anti-corrosion penetrating spray when working.

Part 2: Piston rings and ring grooves
In the case of a 2-stroke engine, there is a pin in the piston ring groove that acts as a joint stopper, and the piston rings are installed in alignment with the pin. In the case of 4 stroke engines, the piston rings move (rotate) during engine operation. If the rings are aligned, the assembly work becomes easier, but if the rings are aligned, an oil passage is created, which may cause the oil to rise and cause white smoke from the muffler.

No. 3: Use of piston ring compressors
When inserting the piston into the cylinder, a piston ring compressor can be used. Experienced mechanics will often use their fingertips or toes to push the piston rings into the groove. This is especially true for small displacement engines, where the tension on the piston rings is low and they are easy to press into place, making bare hand assembly relatively easy. Nevertheless, the use of a piston ring compressor can certainly improve workability. However, no matter how many special tools are available, there are some types of products and engine shapes (stud bolt positioning) that are difficult to use. Just like hand tools, owning a variety of piston ring compressors in different types and sizes is often helpful in a pinch. If you don't have the right size on hand, you can always use a homemade piston ring compressor.

There are various know-hows in engine assembly, and this report is not limited to just the piston and piston ring area. For example, when requesting cylinder boring and honing to a professional shop, the addition of a taper to the piston ring insertion guide (sleeve inner diameter terminal) is also a part of the know-how to make piston insertion easier and more reliable. By carefully checking each assembly point, the engine performance will definitely be improved. Let's enjoy the engine assembly while imagining such a result.

Pk09.jpgWhen requesting a boring operation, it is recommended that the inner wall of the sleeve end be tapered at the same time, so that the piston ring can contract and fit smoothly into the sleeve. If there is enough room in the sleeve wall thickness, it is recommended to request a shallower tapered angle so that the piston and piston ring can be inserted more smoothly.

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