An "assembled" crankshaft has the advantage that it can be disassembled, replaced with damaged parts, and "reassembled. However, this is only possible if replacement parts for repair are available. Even if you have the technology to repair the problem, it will not help if you do not have the parts. At Inoue Boring, we are tackling The KAWASAKI head-on.
Early Z1 will be 50 years old in 2022
The 750RS/Z2 was introduced as the 1973 model in Japan under the "voluntary regulation" of 750cc displacement. Since this model was originally developed for the North American market, the world's largest motorcycle market, a performance model was developed to outperform the CB750 series that was marketed earlier, with a displacement of 900cc (903cc).
Check the current condition before disassembling
When we receive a request for overhaul, we do not immediately start disassembling the machine, but rather begin by checking the condition of the machine before starting the work. If the condition is good, all parts are 5/They say the runout is less than 1000mm.
Even if the crankshaft is centered with no runout, if the 180 degree phase is not correct, the engine performance will not be achieved. Even if the crankshaft has not been disassembled in the past, there are cases where the straight shaft does not stick to the piston pin of the connecting rod, which means it is out of phase.
Disassembly plate and hydraulic press together
The crankshaft was disassembled by combining a U-shaped fixing plate for crankshaft disassembly and a push pin; the press pressure during disassembly is naturally higher than that of the thin crank pin of a 2-stroke engine. All parts were disassembled, but the crankshaft was to be delivered to the client in this condition. Because the crank pin and crank journal had deep worm-eaten rust, we judged that we could not get good results even if we restored them. After consulting with the client, we decided to deal with it that way. In this case, the client had to find a crankshaft with a good degree of quality.
Rust and insect damage common in submerged engines
Remove both outer circlips and inspect the bearing sliding parts. Here, a dark cloud was gathering. There were also rust marks on the outer race of the bearing. Further disassembly revealed worm-eaten rust on a portion of the crank journal. It is a pity because this crankshaft was perfect in appearance and accuracy before disassembly.
Depends on condition of crank pin
The crankshaft overhaul was proceeding smoothly, but we had no choice but to abandon the crankshaft before all the parts were disassembled. It was probably a "submerged engine" that had been left in a disassembled state above the engine waist for a long time.
Manufacture of special bearings for replacement
In anticipation of increased demand in the future, special-size bearings are custom-ordered from a manufacturer that supplies bearings for genuine parts of the manufacturer. The accuracy and reliability of the bearings are the same as those of the manufacturer's genuine parts. The connecting rod side shims are machined and manufactured by iB.
Craftsmanship assembly work
The shine of the connecting rods can only be achieved with the manufacturer's genuine copper-plated finish. Not only a pure overhaul menu, but even a crankshaft that has been used for many years and is stained with oil and discolored can be revived to a brilliant state, depending on its condition. In the past, connecting rods were reused, or good quality parts were used, but in anticipation of increased demand for overhauls, iB now custom manufactures and stocks connecting rods for the Z1. The Z2 connecting rods, which have different connecting rod spans (lengths), are being overhauled on the premise of reuse.
Interviewed in cooperation with iB Inoue Boring Phone 049-261-5833
- Point 1 - Disassembly and overhaul may not be possible in all situations.
- Point 2 - Needle bearings and side shims can be replaced to achieve the "best possible result.
- Point 3 - Packed securely during transportation. Shocks can distort the assembly accuracy.
Repairing the crankshaft is a major undertaking because it requires disassembling the entire engine "below the waist. Without considering the condition of the crankshaft, which converts explosive power into rotational power, it is impossible to talk about engine performance and good or bad engine condition. Since it is not easy to overhaul the crankshaft, it is important to check if it is "centered," bent, or distorted. In some cases, the client is asked only to check the condition of the crankshaft.
The crankshafts for the Z2/Z1 have special bearing sizes and are not generally available. The journal bearings of the crankshafts are not ball bearings, but needle roller bearings. There are no standardized products or products that can be purchased normally, and the only way to obtain them is to place a new order for a large lot = a huge number of units. In other words, they needed to "stock a large number" of special size bearings.
After successfully overhauling crankshafts for the Honda NSR250R series and gaining experience, iB decided that the next task should be to repair and rebuild Kawasaki Z2/Z1 series crankshafts, for which demand can be expected. The key bearings need to be ordered and stocked in large quantities, but this is the first step. We can get through this with the expectation of "increased demand" in the future!
The company decided that it would be able to ride out the problem in anticipation of "increased demand" in the future. The bearings are often damaged, but the crank journals, crank pins, and outer races of the bearings have been heat-treated (hardened) so that there are few cases of wear, and fortunately, there are many parts in good condition that can be reused.
However, there are many examples of engines with poor vehicle or engine storage conditions or "submerged" history that have insect-bite rust due to rust caused by water immersion. Know that when this happens, they can no longer be reused.
The remaining problem is to reproduce the position of the anti-slip lines on the crank journals. This line plays a major role in ensuring accuracy during assembly. On the other hand, if the assembly is done out of the original position, it will be extremely difficult to reproduce the accuracy.
To solve this problem, a special crank assembly jig for the Kawasaki Z series was created to force the crank to be press-fitted in the correct position. Moreover, it is said that there was a lot of ingenuity and trial-and-error involved in the detailed aspects of the jig manufacturing process, but iB, with its extensive experience in manufacturing jigs for machining centers, was able to manufacture all of the jigs in-house.
The completed Z series crankshafts are delivered with a control chart of "centering results" and "accuracy. In addition, the crankshafts are temporarily assembled in the factory crankcase for inspection, and the bearing pin fit and crankshaft rotation are checked before delivery. On rare occasions, there are inquiries from customers who say, "The crankshaft turns lightly at first, but after repeated inspections, a slight snagging occurs." This problem has been confirmed by iB, but the problem can be eliminated if the crankshaft is inspected with the crankshaft installed in the crankcase. By fixing the journal bearing overall with a crankshaft that is dimensionally accurate, the correct centering is achieved and the slight movement of the bearing outer in the axial direction is regulated, resulting in a smooth rotation.