Now that we have pinpointed the cause of the trouble with the lack of kick-off, we should not just restore a simple 2-stroke air-cooled engine.
Here, we will proactively check the condition of each part, which is the minimum we want and need to conduct when we disassemble the engine waist.
- Pitfalls in rushed disassembly and cleaning!
- Check and inspect to avoid damage
- Even a steel cylinder wears out.
- The world’s smallest and largest! The world’s smallest and largest!
- POINT
Pitfalls in rushed disassembly and cleaning!
Extremely Rare Extremely Small Bore Size: With a bore size as small as Φ36.5mm = piston outer diameter, HS90 also uses a cast iron block cylinder. Therefore, it is rare for the cylinder’s inner wall to be extremely worn by normal use, but if it has experienced a seizure, it may leave deep scratch marks. The condition of the inner walls should be thoroughly inspected visually and with the fingertips. For a detailed inspection, carbon contamination must be removed and cleaned. In the case of 2-stroke engines, unburned engine oil can adhere to various parts due to exhaust and compression leaks, which can lead to the accumulation of sludge and various contaminants. When restoring parts, especially the cylinder sludge and oil stains should be cleaned thoroughly. If dirt falls into the engine during the assembly process, it will be a big problem. Before restoration, make sure to clean and remove the dirt in and around the exhaust ports of the cylinders. It is ideal to use a high-performance chemical detergent to remove carbon stains from the pistons, and scrubbing them with water-resistant paper is a big mistake! Especially on the piston skirt side, use chemicals and a soft brush like a toothbrush to clean.
Polishing with waterproof paper, etc. will increase piston clearance and cause mechanical noise.
Check and inspect to avoid damage
A bearing is incorporated in the connecting rod of a 2-stroke engine. If the engine oil runs out and the engine is not lubricated, the rollers of the bearing may attack the piston pin, causing a step in the sliding area of the pin. When disassembling the engine, carefully check the pins and bearings visually. A magnifying glass = loupe is useful for such inspections.
When you have the piston alone, use a loupe to visually check the piston ring groove.
Many engines that have been running for many years have carbon deposits in the ring grooves, and you may notice worn (shiny) areas on the rings. The ideal cleaning method is to use chemicals to dissolve and wash it off without forcing it to be scrubbed with a wire brush.
Even a steel cylinder wears out.
The upper and lower intake and exhaust ports are easily worn and scratched. Regardless of displacement, cylinder wear on 2-stroke engines is most common in this area.
If there are large, deep scratches, the engine is considered to have a history of seizures in the past. If you have oversized pistons and piston rings, we recommend that you have them machined by a professional internal combustion engine machining store with the specified piston clearance. If the engine continues to run in poor condition, other parts of the engine will be adversely affected. To check the condition of the piston rings, insert the disassembled piston rings into the cylinder and measure the gap between the rings (also called “ring gap”) with a thickness gauge. If the bore size is around Φ40mm, the specified value is around 0.3 to 0.4mm, and the usable limit is 0.7mm or more.
In other words, if the use limit is exceeded, the engine will not be able to show its original performance. For such a day, in order to maintain a 2-stroke old car for a long time, it is advisable to have oversized pistons, piston rings, piston pins, and small end bearings as spare parts.
The world’s smallest and largest! The world’s smallest and largest!
The Yamaha Little Twin series has a large number of fans not only in the domestic scene but also around the world. In the racing scene of the 1960s, racing machines modified from the Yamaha Little Twin were known to be very successful in both road racing and motocross (scramble) racing. The exhaust sounds unique to this series model are unique and exciting!
POINT
Point 2 – Care must be taken not to damage it because it is an important component.
Point 3 – Try to recover parts & start the engine in the best possible way.
The process of removing burnt carbon can be tedious. First of all, it is important to know that using water-resistant sandpaper to polish off burnt carbon is the wrong cleaning method.
Using waterproof paper will remove too much carbon, so even if the pistons and cylinders are finished nicely, the piston clearance will be large, and when the engine is started after assembly and restoration, the mechanical noise will be loud.
With the rise of high-performance chemicals, such cleaning work is becoming relatively easy.
Unburned carbon that has accumulated and adhered to the piston should be thoroughly removed, but as mentioned above, water-resistant paper (sandpaper) and metal brushes should not be used extensively. It is advisable to use a powerful and high-performance spray-type carbon cleaner or an immersion-type cleaning cleaner. Remember that parts cleaners for degreasing and cleaning purposes, which are often found in jumbo cans, can be used as finishing cleaners after carbon removal, but they are simply a waste of money since they cannot be effective against carbon stains.
Reconfirm cleaning points after engine disassembly here.
(1) If carbon stains are severe, prepare a strong carbon cleaner chemical, multi-cleaner, or soaking type carb cleaner, and cut and use a container such as a plastic bottle that is about one size larger than the part size. By soaking the parts in the chemical without waste, the work can be carried out efficiently. Also, heating the cleaning solution to around 40 degrees Celsius improves the cleaning activity.
(2) In the case of soaking cleaning solution, wait for a while after soaking in the solution, and when the carbon surface begins to dissolve, wash it off with a nylon brush.
When the surface of the carbon has been removed to some extent, soak it in the solution again and wait for a while, and then wash off the floating dirt with a nylon brush again. This process is repeated. An effective measure for working in cold weather and for improving work efficiency is to heat the cleaning solution. Even if the temperature is 40 degrees Celsius, the same as that of a bath, the chemicals will be activated, and the work efficiency will be greatly improved. Let’s improve work efficiency with our ideas.