The old car movement produced before the 1980s is no longer a passing fad. The two-stroke engine, which is even considered an endangered species, will not perform at its best unless the crankshaft, the heart of the engine, is in good condition. Such engine parts are not to be replaced but "repaired" is the norm now and in the past. Let us reconfirm what crankshaft repair for large-displacement 2-stroke engines is all about.
The age of disassembly and repair instead of ASSY replacement
The crankshaft for the Kawasaki 500SS after the oil seal, bearings, crank pin, and big end bearing has been replaced through an overhaul. When the sealing performance of the oil seal, called the center seal, deteriorates, the primary compression of each cylinder goes back and forth, and the original explosive combustion cannot be obtained. This would result in unstable idling and a lack of punch during full acceleration.
Craftsmanship for deft, high-precision assembly
Before disassembling, the main dimensions are measured, and then the parts are disassembled in an efficient manner.
Each disassembled part is cleaned with wire buffing, etc., and then assembled according to the dimensional data before disassembly. Parts for the popular 2-stroke Kawasaki H1 and H2 models are sold as special parts in the form of connecting rod kits that include connecting rods, crank pins, bearings, side metals, and other components. The manufacturer's genuine repair parts have long since been discontinued.
The final finish is determined by craftsmanship and intuition.
Assembled by craftsmanship using a hydraulic press. Using an inspection table, the center and runout of the crank are measured with a dial gauge. The crankshaft is assembled in a very efficient manner while gradually improving the assembly precision. During the final adjustment, the crank web is struck with a large copper hammer to reduce the runout value.
Before -> After at a glance
Before repair work
After repair work
The crankshaft, which was dirty and blackened with carbon before the request, was revived to a different beauty upon completion of the overhaul. Not only the beauty but also the centering and runout removal of the crankshaft is done to the best of our ability.
Semi-permanent labyrinth seal
Yamaha vehicles have used a non-contacting labyrinth seal that can be used semi-permanently instead of an oil seal since the 250YDS3 (1964 model). This technology has recently been converted to 2-stroke multi-engine models from Kawasaki and Suzuki, and crankshafts with labyrinth seal specifications, which were also adopted for the Honda NSR250R, where the center seal was a weak point, have been very popular. Inoue Boring (Kawagoe City, Saitama Prefecture), which cooperated in the photo shoot, is actively promoting the revival of 2-stroke crankshafts through labyrinth seals.
A fully restored bike that is not only finished in appearance but also finished inside the engine can be loved and used for many years to come. It is advisable to overhaul the engine as much as possible for the future of the bike.
Photography by: iB Inoue Bowling
POINT
Point 1 - If new parts are not available, disassemble and repair.
Point 2 - Hire an internal combustion machine machinist for high-precision workmanship.
Point 3 - For multi-engine, go from oil seal to labyrinth seal.
Internal combustion machining of crankshafts involves crankshaft disassembly, parts replacement and assembly, and centering. Dynamic balancing is one of the crankshaft's internal combustion machining operations, in which an integrated crankshaft that cannot be disassembled is continuously rotated at high speed on a special device and balanced in this state. In the case of an assembled crankshaft, dynamic balance cannot be measured because the connecting rod is built in (i.e., it is not possible to balance the crankshaft by swinging the connecting rod around).
There are now only a few internal combustion machinery companies that can perform "disassembled assembled crankshaft centering. Here at Inoue Boring in Kawagoe City, Saitama Prefecture (which will be in business for 69 years in 2022), we were able to photograph an overhaul of an assembled crankshaft. If we rank order intake volume by model:
No.1 ◆Yamaha RZ series
No.2 ◆Honda 4-stroke mini-series of Monkey and Ape
No.3 ◆2-stroke, 3-cylinder Kawasaki Trible and Suzuki GT series
They say that this will be the case. As an extra, the number of crankshafts for Kawasaki air-cooled Z series and Honda NSR250R is increasing every year. Regardless of the number of crankshafts, Inoue Boring receives orders for internal combustion engine machining and repair for a wide variety of models.
When it comes to machining repairs, it is essential to prepare replacement parts. Inoue Bowling has some replacement parts in inventory for popular models, so if you notice a problem such as rattling in the connecting rod or noise coming from the crank bearing when disassembling the engine, you may want to consult with Inoue Bowling through the bulletin board on the Inoue Bowling Web site.
There are certainly cases where "all is not well" if new parts are lost. However, it is important to know that some engine parts can be revived through "repair" rather than parts replacement. It is also a wonderful thing that internal combustion machine processing pro stores are able to materialize the revival of such engine parts.
