The term "bad engine condition" is not always the most reliable one. Sometimes the engine does not blow up well or does not idle. Is it really due to a malfunction of the engine itself? Let's take a look at the basics of engine maintenance, the first step in checking the condition of the engine.
There are adapters for different plug sizes.
Some adapters measure compression by pushing a measuring rod with a triangular rubber end into the plug hole, but this type of adapter allows the operator to use both hands by tightening and securing it to the plug screw. When stepping on the kick, the throttle must be fully opened and stepped on forcefully and continuously 6 to 7 times to measure the correct data. In the case of a cell motor, connect a battery booster, open the throttle fully, and keep the cell motor running vigorously and continuously for 7 to 8 seconds to measure the data.
If multi-engine, focus on cylinder-to-cylinder balance.
For a single-cylinder engine, data measurement is quick, but for a four-cylinder engine, the same four-cylinder compression must be measured under the same conditions. When measuring data for a CV carb, even if the throttle butterfly is fixed at full open, the CV valve will not open fully. By removing the air cleaner and forcing the valve to lift, we can measure the exact compression data. When you want to know the relative comparative balance of the 4 cylinders, you can use the normal throttle fully open measurement. It is important to measure under the same conditions.
Connection hose made by a reliable Japanese manufacturer
In the case of the triangular pyramid rubber end measuring rod push-on type, the measuring adapter is often of the metal pipe type that does not expand. In the case of rubber hose adapters, however, the expansion of the hose itself can cause variations in measurement data. Even if several types of compression gauges are used and the same cylinder is used, the measured values may differ depending on the expansion of the hose itself. Adapters made of reliable Japanese rubber hose seem to have less expansion and less variation in measurement data.
Setting with reference to the burnt condition of the plugs
As a general impression, older engines with small-displacement single-cylinder engines seem to have higher compression pressure, while older engines with large-displacement multi-engines seem to have lower compression pressure. Therefore, even among 4-stroke engines, it is not possible to simply compare compression pressure data numbers. Incidentally, the actual compression data for the KZ550 with the high-compression piston installed was about 200 kpa higher than that of the stock engine.
POINT
Point 2 - Compression pressure gauges that can determine good compression are used by both Sun mechanics and professional mechanics.
Point 3 - Identify compression pressure gauges with high-performance rubber hoses that do not expand easily.
The engine elements of good performance are called good fuel, good compression, and good explosion.
Even though it is called the good engine trifecta, it is good compression that is directly attributable to the engine itself.
Good fuel is = gasoline.
If the gasoline is fresh, it is good, but if the vehicle has been left unused for years, the gasoline is often not fresh and not a good fuel. So-called rotten gasoline does not start the engine smoothly. If the gasoline smells different or has reduced volatility, it is a good idea to drain all the gasoline inside the tank, replace it with fresh gasoline, put a rag under the carburetor, open the float chamber drain bolt, and use the fresh gasoline to push the old gasoline and It would be a good idea to push the dirt away.
A good explosion includes the gasoline element mentioned above, but the explosion we are focusing on here is the electrical system. A good explosion cannot be obtained unless a good spark flies. Not only is the spark strong, but its timing is also extremely important. It depends on the engine specifications (is it an old car engine? Is it the latest model? It depends on the compression ratio and cam timing), but generally the ignition timing at idle is 8 to 15 degrees before the top dead center (BTDC). The maximum advance angle is around 25 to 30 degrees for most production cars. Incidentally, in the case of the Honda Cab Racing CR110, an old racing car that can be called the symbol of the rotary horsepower type engine, the fixed advance angle of 55 degrees is the standard specification! Street models were equipped with an advanced angle governor, but the set value was very different from that of ordinary production models such as the Super Cub.
A special tool called a compression gauge or compression tester is indispensable to know what kind of compression is good and what kind of condition the engine is in. By removing the spark plug, placing a fingertip lightly on the plug hole, stepping on the kick arm, or pressing the starter button, you can hear the sound of the engine compressing.
In fact, there is a difference in the sound that sounds energetic, and the feature of the compression gauge is that it can be converted into a numerical value and confirmed visually.
Excessive running can cause piston ring wear and compression leaks due to sticky contact between the intake and exhaust valve seats and valve faces. The accumulation of such negative factors causes changes in compression conditions, which gradually worsen. Compression data is different for each engine. The standard values and usage limits of the parts are based on the data provided in the genuine service manual of the motorcycle manufacturer, but above all, the situation cannot be judged without actual measurements.
Generally, measurements are taken after the engine has been started and warmed up to a certain degree. For single-cylinder engines, this is fine since there is only one cylinder, but for engines with two or more cylinders, it is also important to take actual measurements on all cylinders and compare the data. For engines in poor condition, the values are clearly lower than the standard pressure, and for multi-engine engines, the values may vary in some cases.
In the case of a tuned engine with kit parts such as bore up or high cam, after the test run & settings are made, how has the current status changed compared to the data before incorporation or the standard data in the service manual? It is also important to confirm this.
Since the condition of a 4-stroke engine can be judged by knowing the compression data or, in the case of a multi-engine, by the balance between cylinders, the compression tester can be said to be an extremely important special tool for the Sunday mechanic who loves engine maintenance.
