I heard from a motorcycle buddy that he wanted to replace the piston rings, so I disassembled the engine above the waist and inspected the surrounding parts at the same time. In this section, I will focus on the carbon removal method, which must be done when replacing piston rings. Carbon stains on the piston tops should not be polished off, but rather "dissolved with chemicals for a beautiful finishing is the correct answer.
- Small engines are easier to unload and work with!
- Disassembly above the waist is relatively easy, but ......
- Be careful not to lose the pink lip hookah.
- Visual check of the cylinder inner wall
- Piston disassembly on a spread rag
- Carbon removal chemicals are effective
- Check the gap between the piston rings.
- Piston clearance is also roughly checked.
- The orientation of the common name expander ring
- Straight piston ring compressor
Small engines are easier to unload and work with!
Experienced mechanics and professional mechanics prefer "engines with good access" to the part they want to repair. This is a natural tendency. The faster you can get to the part you want to replace, the faster you can get the job done. In this sense, the Honda 4 mini "vertical engine", which cannot be disassembled from the cylinder upwards (commonly known as the "engine waist up") without lowering the engine, is not as easy to service as the horizontal engine, which can be disassembled from the waist up. It can be said that the reason why the horizontal engine of Super Cub and Monkey is said to be "easier to maintain" is exactly because of this. However, even with a horizontal engine, it is much easier to disassemble the motorcycle with the engine down. On the other hand, it is also good to do the inspection and cleaning of the part which is not usually done by lowering the engine at the same time. If you are a Sunday mechanic, you should think so.
Disassembly above the waist is relatively easy, but ......
After disassembling the parts around the cylinder head, you can start extracting the cylinder. For example, the parts around the camshaft should be separated by part and put in a tray. When waiting for parts to be delivered, store disassembled parts in plastic bags so that you do not have to look for them during assembly. In the case of Honda vertical engines, there is no need to disassemble parts such as the cam chain tensioner that are built into the cylinder. However, if the cam chain tensioner slipper is deteriorated and hardened, and the cam chain marks are worn out, disassemble and replace with new parts.
Be careful not to lose the pink lip hookah.
When disassembling the piston, remove one side of the piston pin clip. Then, push out the piston pin from the other side. By pulling out the piston pin, you can remove the piston from the connecting rod. Check to see if the piston pin sliding part of the connecting rod is burned and changing color. Check it.
Visual check of the cylinder inner wall
Once the cylinder has been removed, hold the inside wall of the cylinder up to an outside light or fluorescent light and check it carefully for partial wear or scratches.
Piston disassembly on a spread rag
The tops of the pistons were blackened with carbon as a reflection of the twists and turns that took place before the settings were determined. If you continue to ride the motorcycle under the set condition, it will not be black like this but dark brown at best. The exhaust valve side would be white from the waste heat.
Carbon removal chemicals are effective
I sprayed the piston tops with Daytona gasket remover and wrapped the pistons with packing wrap. In the warm summer, the reaction is fast and easy, but in the cold winter, the chemical reaction is not so good. In such a case, it is good to accelerate the reaction by wrapping the piston with plastic wrap or putting it in a plastic bag. After spraying chemical, wrapping with plastic wrap, scrubbing with a soft brush and ......, I was able to remove the carbon stain from the piston top completely after repeating this process 2 or 3 times.
Check the gap between the piston rings.
Set the removed piston rings = top and second oil x 2 into the cylinder sleeve and push them horizontally using the piston. I measured the gap between the piston rings in the cylinder. If the bore size is 57mm, the gap between the rings is about 0.20 to 0.35, and if the gap is over 0.50mm, the rings need to be replaced. For these piston rings, the gap was 0.3 mm, which is within the specified range. However, the gap was still about 0.05mm narrower when measured with new piston rings, so I replaced the rings with new ones. The rings can be reused for street use. The removed used rings were kept as spare parts.
Piston clearance is also roughly checked.
When measuring piston clearance, use a cylinder bore gauge to make sure that the value is + to the actual measured bore of the piston (clear to the nearest 1/100 mm). When boring new pistons to oversize, specify the finished value of the cylinder bore relative to the actual measured bore and ask the internal-combustion engine store (boring shop) to do the work. For example, if you have a 57mm diameter cast piston and you want to reduce the clearance to 3/100mm, you should specify that. Here, I inserted the piston into the cylinder and inserted a thickness gauge into the gap between the skirt and the cylinder. Then I was able to insert the 0.03mm gauge, but not the 0.04mm gauge. In other words, I can roughly confirm that the piston clearance is between 0.03 and 0.04mm.
The orientation of the common name expander ring
The old piston rings were made of cast iron with a thick oil ring, but in the mid 70's, they evolved into a 3 piece structure, with two hagane rails on the top and bottom plus a ring spring, commonly called an expander, holding them together. The top and bottom of the expander ring should be installed so that the contact point is on the upper side. The rails should be set so that the rail mating point is offset from the expander mating point by about 10 to 15 degrees.
Straight piston ring compressor
This is the original piston ring compressor from Straight, a nationwide chain of tool shops. This product is designed for small diameter bores, but it's much easier to use than you might think. After setting the piston ring angle, set this plastic compressor in place and shrink the rings with your fingertips. While holding the cylinder sleeve edge against the compressor edge, tap the head gasket surface to slide the piston ring into the cylinder with the suit still compressed.
- Point 1: If you want to prioritize workability, disassemble and maintain the engine above the waist with the engine down.
- Point 2: Carbon will damage the parts if it is scraped off, so let's make good use of chemicals!
- Point 3: When you have removed piston rings and new piston rings for replacement, measure the mating gap and compare them.
- Point 4: Let's also pay attention to the vertical relationship when incorporating the oil ring expander.
When the engine is disassembled and parts are replaced, it is necessary to remove the carbon from the piston tops and combustion chambers. If the engine has been used for a long time, you will be surprised to see how dirty it is. When disassembling the engine above the waist, it is important to check the condition of each part. In the case of the cylinder head, the camshaft journals (bearing part) and cam holders should be checked for sliding and rotating conditions. Are there any scratches? The inspection items are whether it turns smoothly. Next is the operation of the rocker arm and shaft. Also, the wear of the camshaft and rocker arm slipper surface must be checked.
If the intake and exhaust valves are removed, the rattle and wear of the valve stems and valve guides can be inspected. It is also possible to check the contact between the valve seat and the valve face. When the intake and exhaust valves are disassembled, the valve faces should be cleaned of dirt and carbon, polished, and then "rubbed" against the valve seats. If the width of the valve seat is wider than the specified value, it is better to ask a professional shop for internal combustion engine machining without hesitation. The work includes grinding the valve face, cutting the valve seats, and rubbing them together. If you notice any wear between the valve stem and the valve guide, and if the valve stem (shaft) is rattling, then you will need to have the aforementioned work done, including replacing the valve guide. If the seat is cut with a rattling valve guide, you will not get a good result. The internal combustion engine will not give good results unless the total condition is restored.
When replacing piston rings, the wear of the piston itself and the cylinder must also be fully considered. The piston ring's job is to rub against the cylinder in a high temperature environment and repeatedly move back and forth. They are the first part to wear out, but it is important to know that under some circumstances (such as poor lubrication), the inner walls of the cylinder can also wear out at the same time.
The important thing to remember when removing carbon is to use as much "chemical power" as possible. If you use a scraper or cutter blade too much, it is easy to scratch the piston. Also, using water-resistant sandpaper will polish the surface of the piston too much, which may result in wear and tear. It is important to know that carbon removal is surprisingly easy when using high performance chemicals for dirt removal cleaning. In this case, we used Gasket Remover (old package shown in the image), but in winter when the reaction is low, wrap the dirty area with a plastic bag or packing wrap. The chemical reaction will be improved by such a step. I've also used a desk lamp on the workbench to warm up the parts, and that worked well too. However, it is very dangerous to overheat the parts and to keep an eye on them while working, so you have to be very careful.
