market dynamics
Big row of motorcycle crankshaft after the hot car is not good to start, ignore the maintenance difference of multi-cylinder car is the main reason!
Release date:2021.07.15

A member friend repaired a Kawasaki ZXR250RR motorcycle, because the crankshaft of the car was damaged, he replaced it, but unexpectedly, after the crankshaft was changed, the car could not be hot. My friend was puzzled and asked me to help him have a look.

The hot car is not good to start the phenomenon, from the theoretical analysis, there may be several reasons.

First, the inlet and exhaust valve clearance of the engine is small or no clearance;

Second, the replacement of the crankshaft and crankshaft, connecting rod tile with abnormal clearance, cylinder and piston, piston ring with abnormal clearance, assembly of the engine in some places assembly is too tight, resulting in increased friction resistance;

Third, improper carburetor adjustment;

Four is the ignition system problems, such as igniter, ignition coil, trigger coil, etc.

Now that you know what's going on, check it site by site. First check the ignition system, unscrew the high pressure cap, check the jump fire intensity of the high pressure spark, which is relatively normal, and then check the valve clearance, the clearance of the inlet and exhaust valves are within the allowable value range.


But found in the inspection process, hot car when the starter motor crankshaft speed significantly lower than the cold car speed, this suggests that the fit clearance problems in some parts of the engine, which can result in hot state engine internal friction resistance is big, so that the crankshaft turn velocity less than demand, lead to hot car the car. Even if the car is in this state, because the motorcycle resistance continues to exist, will reduce the engine power output, will certainly be more fuel consumption.

When I discussed with my friend where the friction resistance caused by the fit clearance might be generated, I realized that my friend did not mark the piston of each cylinder when repairing the decomposed engine before. In the assembly, the corresponding relationship between the piston and the original cylinder was confused, and it was installed at hand.

Listen to a friend said, the reason is basically clear, this kind of old multi-cylinder car, the cylinder, piston, piston ring in the engine have been run in, and the running in condition of each cylinder in the four cylinders is different. In addition, four big Japanese company in assembling the engine, the cylinder, piston, piston ring are respectively depending on the parameters of the finished product selection, so in the disassembly, if there is no make the mark, make corresponding relation, will appear between the cylinder and piston clearance changes, as temperatures rise, the fitting clearance fit clearance will be less than normal, Make the friction resistance more and more large and the above failure situation.

To break down the engine, the use of cylinder table with micrometer to measure the size of the four cylinder and the piston, the cylinder liner wear large selection of larger diameter of the piston and cylinder liner wear small selection of the smaller piston diameter, after completion of assembly, situation has improved a lot, but when hot car, or a bit of a bad car, but the situation has improved, only when the temperature is very high.

Further compensate for cold mill way right now, the water inlet of the pump on the water taps, cylinder head outlet ends don't meet, let the water directly put off, start the engine, the idle speed to 3000 r/min, 3 ~ 4 hours continuous work, here try not to let the engine temperature rises too high, also cannot let the temperature is too low, some friends might say, How is the temperature controlled? There is actually a little trick here, is can adjust the water faucet to control the engine temperature. After the cold grinding is completed, the retrial, the hot car is not good to start the problem solved!