Maintenance Typical repairing failures and how to avoid them

Install piston in reverse

At the top of each piston is a marking, usually a triangle or arrow. The arrow indicates which side of the piston should go to the exhaust port. The pin for fixing the rings must not be on the side of the exhaust opening, because the ring can easily get stuck, a piece of the piston can break off, and this will destroy the cylinder. So the arrow always points towards the exhaust opening, while the fixing pin(s) are on the opposite side, but not necessarily in the middle.

Using a candle with the wrong heat value

Tuned engines operate at higher temperatures because of increased compression, increased fuel intake, and increased power. The candle must withstand this as well, and it must function accurately even under higher loads. Compared to the factory one, you should always use a candle with a higher calorific value. Manufacturers of tuning parts usually provide precise instructions for this as well. If there is a candle with a lower heat value in the engine, it will overheat under load, and the gasoline-air mixture will ignite prematurely. This increases the heat load on the piston, which can cause it to stick and burn. In extreme cases, the top of the piston can also be punctured.

Exhaust overtightening, bad fixing

When installing the exhaust, the screws on the cylinder must only be tightened so that the exhaust does not blow out. Before installation, the connecting surfaces must be checked to see if they are suitable, and if necessary, repaired and leveled. A new gasket must be used for each installation. If the screws are overtightened, the thread will be damaged, the screws may break.

The exhaust must always be secured without tension, the screws must not be tightened separately. Each screw must be screwed into place, by hand, until it stops. After that, if it is properly in place, it can be fixed with the necessary torque. Stresses arising in a poorly fixed exhaust lead to cracks and later breakage.

Use of too small main nozzle

In the case of factory 50 scooters, a main nozzle that is too small usually only results in a loss of performance, while during tuning, after conversion to a 70, it can lead to fatal damage. When carburating the scooter, we always work our way down from the larger nozzle size until we find the ideal setting. The good setting can be determined based on the candle color image. By reducing the size to the ideal setting, the performance increases and the engine becomes more and more "sharpened". The scooter is "sensitive" to more and more small things: temperature changes of a few degrees, humidity, long journeys, high-speed use. It can break down, overheat, and seize more and more easily.

Seals, bearings that are still "good"

A common error is that old bearings and shim rings are returned to the new crankshaft. The bearing may have invisible, imperceptible defects. In vain is it washed and oiled, in vain does it make a sound when spinning. The factory bearings cannot be used in the tuned engine either, because a larger clearance may be required. (due to higher heat, C3 should be replaced with C4). The shim rings, bearings and cylinder head gaskets are used once. After disassembly, they cannot be put back together if we want to do professional, long-lasting, reliable work. The price of such parts is a fraction of a crankshaft or cylinder, so it is not worth saving on them.

Using the wrong oil

The key word here is appropriate. You don't need the most expensive, best oil. Not even the HUF 600-1000 liquid that looks like oil but doesn't fulfill its function. Oil manufacturers make special scooter oil. We can also find a variety of them, semi-synthetic, synthetic, there is also one for directly tuned scooters. The too "good" or too low-quality engine oil can cause coking, ring sticking, and can also destroy the spark plug. The exhaust opening is also frequently loaded, the diameter of the opening decreases, which restricts the engine's performance. High-performance racing oils are designed for high temperatures, if the scooter does not operate at this temperature, the oil cannot burn completely and this leads to coking.

Replace bearing using a hammer

The bearings and crankshaft are always fitted with an overlap, the diameter of the crankshaft is several thousandths larger than that of the bearing. This prevents the bearing from rotating. On the other hand, this makes things difficult for assembly.

When disassembling the old bearing, you must proceed very carefully, do not hammer or grind off the old one. It is best to use a bearing puller. If this is not available, grinding may be the solution, but it must be done very precisely and must not damage the tread of the skimmer ring. In this case, it is worth folding a small plate onto the surface. The components do not have to be tapped into place during installation either, but can be installed by heating without mechanical damage.

By heating the bearing and cooling the shaft, the change in size due to thermal expansion is enough for the bearing to slide smoothly into place. After cooling down, the essential part of the tuning scooter is firmly and precisely in place. When heating, care must be taken if the bearing has a plastic basket, so that it does not overheat and melt or be damaged! The crankshaft must be placed in the refrigerator with noble simplicity, and the bearing can be placed on a relay. Do not heat the plastic basket bearing above 100°C.