Practice Piston Ring Replacement If You Wish to Keep on Riding for a Long Time.

I heard from a motorcycle buddy that he wanted to replace the piston rings, so I disassembled the upper part of the engine 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!

Experienced and professional mechanics prefer "engines with good access" to the part they want to repair. That would be a natural trend. The faster you can access the part you want to replace, the faster you can get the job done. In this sense, the Honda 4 mini "vertical engine" cannot be disassembled from the upper part of the cylinder without lowering the engine, and is not as "serviceable" as the horizontal engine, which can be disassembled from the above part of the engine without removing the engine from the vehicle. It can be said that this is the reason why the horizontal engines of the SUPER CUB and MONKEY are said to be easier to maintain. However, even if it is a horizontal engine, it is far easier to work with the engine down when disassembling the upper part. On the other hand, it is also a great opportunity to unload the engine and inspect and clean the parts that are usually difficult to do at the same time. If you are a Sunday mechanic, you may want to think about this as well.

Disassembling the upper part is relatively easy.

After disassembling the parts around the cylinder head, start extracting the cylinder, and keep the removed parts in order by part. For example, the parts around the camshaft should be sorted by part and placed in trays. When waiting for parts to be delivered, store disassembled parts in plastic bags so that you don't have to look for the parts during assembly. In the case of Honda vertical engines, there is no need to disassemble parts that are built into the cylinder, such as the camshaft chain tensioner. However, if the camshaft chain tensioner slipper is deteriorated and hardened, and the camshaft chain marks are worn, disassemble it and replace it with a new parts.

Be careful not to lose the pin clip.

When disassembling the piston, remove one side of the piston pin clip. Then push the piston pin out 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.

Visual check of cylinder inner wall

Once the cylinder has been removed, hold the inner wall of the cylinder up to the outside light or fluorescent light and check it carefully for any partial wear or scratches.

Disassemble the piston on a spread rag.

The tops of the pistons were blackened with carbon, reflecting the twists and turns before the settings were decided. If you continue to drive in conditions where the settings are set, it will not be pitch black like this, but dark brown at best. The exhaust valve side would be slightly white from the waste heat.

Carbon removal chemicals are effective.

I sprayed the tops of the pistons with DAYTONA gasket remover and wrapped the pistons in packing wrap. In the warm summer months, the chemical reacts quickly and is easy to work with, but in the cold winter months, the chemical does not react as well as it should. In such cases, it is best to wrap a plastic wrap around it or put the piston inside a plastic bag to accelerate the reaction. After spraying the chemical, wrapping it with plastic wrap, scrubbing it with a soft brush, and repeating this process 2 or 3 times, I was able to completely remove the carbon stains from the piston tops.

Checking the piston ring mating gap

Set the removed piston rings = top second oil x 2 into the cylinder sleeve and push it horizontally with 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. There is no problem in reusing it for street use. The removed used rings were kept as spare parts.

Check piston clearance roughly.

When measuring piston clearance, it should be strictly measured with a cylinder bore gauge to ensure 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 facing of the common name expander ring

In the past, piston rings were made of cast iron with thick oil rings, but in the mid 70's, they evolved into a 3-piece structure, with 2 steel rails on the top and bottom plus a ring spring, commonly called an expander, holding them in place. The top and bottom of the expander ring should be installed so that the meeting point is on the upper side. The rail should be set so that the rail mating point is about 10 to 15 degrees from the expander mating point.

STRAIGHT piston ring compressor

This is the original piston ring compressor from STRAIGHT, a chain of tool stores in Japan. This product is designed for small diameter bores, but it is much easier to use than I imagined. After deciding the setting angle of the piston rings, set this plastic compressor in place and shrink the rings with your fingertips. While holding the edge of the cylinder sleeve against the compressor edge, tap the head gasket surface to slide it down the cylinder and insert the suit and piston into the cylinder while keeping the piston rings compressed.

When disassembling the upper part of the engine and practicing the replacement of parts, "carbon removal" of the piston top and combustion chamber area is essential. If the engine has been used for many years, you will be surprised at how dirty it is. When disassembling the upper part, the condition of each component should be actively checked. In the case of the cylinder head, check the camshaft journals (bearing parts) and camshaft holders for sliding and rotating conditions. Are there any scratches? Does it turn smoothly? Next, check the operation of the rocker arm and shaft. Also, check for wear on the camshaft mounts and rocker arm slipper surface.

Once the intake and exhaust valves are removed, the rattling and wear of the valve stems and valve guides can be inspected. This will also allow you to check the contact between the valve seat and the valve face. Valve seat contact is extremely important in engine condition, so when you disassemble the intake and exhaust valves, remove dirt and carbon from the valve faces, polish the valve faces, and then "rub" them against the valve seats. If the width of the valve seat is wider than the specified value, it is better to ask a professional internal-combustion-machining store to do the work without hesitation. The work would include grinding the valve face, cutting the valve seat and rubbing it together. If you notice that there is wear between the valve stem and the valve guide, and that the valve stem (shaft) is rattling, you should request the aforementioned work process, including the replacement of the valve guide. Cutting the seat with a rattling valve guide will not give a good result. An internal combustion engine will not give positive results unless the total condition is restored.

When replacing piston rings, 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 make repeated reciprocating movements. It is the first part that is supposed to wear down, but it is important to know that under some circumstances (due to poor lubrication, etc.), the inner walls of the cylinder can also wear down at the same time.

In this case, I removed the carbon deposited on the piston that was made into a single piece, but the important thing in carbon removal is to use the "power of chemicals" as much as possible. If you use a scraper or cutter blade too much, it is easy to scratch the piston. Also, using water-resistant sandpaper can polish the piston surface too much, resulting in abrasion. When it comes to dirt removal cleaning, you should know that it is surprisingly easy to remove carbon by using high performance chemicals. In this case, I used gasket remover, which works well for removing carbons (the image shows the old package), but in winter when the reaction is low, wrap the dirty part with a plastic bag or packing wrap. This will improve the chemical response. I have also warmed the parts by shining a desk lamp on the workbench, which also worked well. However, it is very dangerous to overheat the parts or to let them out of your sight while working, so you have to be very cautious while working.

See Accessories of DAYTONA