If the cylinder is worn out, go back to the drawing board with "sleeve fabrication".

When genuine repair parts for 2-stroke engines were relatively plentiful, the manufacture of cylinder sleeves was an extremely rare processing technique that was rarely discussed. However, every year, more and more enthusiasts of 2-stroke engines are requesting the manufacture of sleeves, regardless of the cost. What exactly is this "sleeve fabrication" that is attracting so much attention?

2-stroke engines have many enthusiastic followers regardless of the model

Many models, like the Kawasaki Triple series, were developed with engine output as a priority, and often have large intake and exhaust ports that catch the reciprocating pistons on their port edges, wearing down the sleeves and increasing engine noise.

Although the complicated machining process and high precision required for the new sleeves make them costly, many enthusiastic 2-stroke engine believers are returning to the "Furidashi". In particular, the number of requests for work on Kawasaki's air-cooled 2-stroke triple series engines is said to be overwhelming.

New sleeves that also allow full copying of port shape and port height + alpha

Cylinders for the 750SS/H2 are no longer easy to obtain parts for. The company has undertaken numerous sleeve production replacements in the past, and currently has extensive experience with ICBM® cylinders, which are aluminum sleeves with a special plating treatment.

Even for single-cylinder engine cylinders, a dummy sleeve is first fabricated and inserted into the cylinder with the sleeve machined off. The process begins by checking that the shape and height match the intake and exhaust ports and scavenging ports on the block side.

The regular sleeves are machined while data is measured and corrected; the 2-stroke sleeves have various ports for intake, exhaust, and scavenging, so the cylinder shape is different from that of a 4-stroke engine.

Once the sleeve is press-fitted into the cylinder barrel, each port step is finished with a ruter. Only after this stage can the normal boring and honing operations begin.

Internal combustion engine machining technology that meets the expectations of 2-stroke engine fans

At the iB Inoue Boring site, many sleeves in the process of development & fabrication can be seen on the machine side. The fact that there are sleeves not for the same machine model, but for a variety of models, gives an idea of the large number of requests for sleeve production.

The sleeve for the first generation Yamaha RZ is still the model with the most orders. In many cases, the damaged cylinder bores were shaved and enlarged, and the aluminum sleeves were re-plated and finished. The aluminum sleeve on the right is for the NSR250R.

Development of a Special Jig to Improve Reproducibility of Press Fit

Special jig developed by iB Inoue Boring to press-fit sleeves for NSR250R and RZ250R. This jig is used to prevent press-fit variation and is finished to a high degree of precision.

The NSR250R's intake and exhaust plus scavenging ports are very different in shape compared to the high-performance 2-stroke engines of the air-cooled engine era; the "pillars" in the ports that prevent piston swiveling contribute greatly to its high performance.

The sleeve is press-fitted into the cylinder barrel by means of a hard-fit. Without a jig, repeatability cannot be obtained, and individual cylinders will vary.

　　　　　　　　　　　　　　　　　　 Photo by/iB Inoue Boring www.ibg.co.jp

When piston x cylinder seizure or piston clearance reaches the wear limit, it is essential to utilize oversize pistons and perform boring and honing work to match the piston outer diameter. However, there is a limit to oversizing, and once the maximum size is reached, the cylinder must be replaced with a new one. Many riders must have experienced such a situation, especially in the case of 2-stroke engines, which have a large number of enthusiastic followers. Today, however, new cylinders are hard to come by, so the technique of grinding down the sleeve inside the cylinder, press fitting a new sleeve, and rebuilding the engine is becoming the norm.

iB Inoue Boring is a company that specializes in the refurbishment and processing of internal combustion engine parts. When machining a new sleeve, the company begins by making a dummy sleeve for dimensional confirmation, rather than cutting a finished product out of the box. After confirming the height and width of each port and, depending on the model, the port angle, the dummy sleeve reflects the data and the production sleeve is machined on a CNC machining center. The production cost is not cheap due to the various processes involved, but the number of users who want to replace the sleeves has been increasing year by year. The number of users who want to replace their sleeves has been increasing year by year, and the company is now receiving requests for reproduction on a daily basis.

As you can see, the Kawasaki 750SS/H2 cylinder shown here also has a new sleeve press-fitted. iB Inoue Boring has undertaken a number of internal combustion engine rebuilds and modifications, especially for the Kawasaki 2-stroke air-cooled triple engine series. Once the sleeve can be rebuilt, as long as STD (standard size) pistons can be procured, it is possible to start over with the same bore size as in the catalog data.

Currently, ICBM® with aluminum sleeves and special plating treatment has many achievements, and cast iron ICBM® with cast iron sleeves and cylinders with special plating treatment has also been developed, and has been used for cast iron cylinders of Harley-Davidson and Kawasaki 650W1 series before the 1970s, and has been well received. It has been well received. In the next engine overhaul timing that comes along, let's try to "extend the life of internal combustion engines" with modern technology.