market dynamics
Motorcycle maintenance combat valve leakage
Release date:2019.07.31

1. Valve leakage detection method:

Method a,

First of all, the cylinder pressure is not enough, the starting rod is not too fast to step down a few times feel no resistance or resistance is very small. If the cylinder pressure is insufficient, it indicates air leakage, but not necessarily valve leakage. Check whether the spark plug is tightened first, and if it is not tightened, check again. If the cylinder pressure is still insufficient, unscrew the spark plug, put 10 ml of clean oil into the spark plug hole, tighten the spark plug, and then use the starting rod to test the cylinder pressure several times. If the cylinder pressure is sufficient, it is piston ring leakage; If cylinder pressure is still insufficient, make sure it is valve leakage.

Method 2,

1. First remove the hose or screw from the spark plug, exhaust muffler and intake pipe. Please pay attention to the process screw set on the intake pipe for detecting cylinder negative pressure value, such as Honda CB125T model; There are rubber hoses on the intake pipes of scooter engines to the negative pressure switch, such as Honda CH125 water-cooled scooter (black shark model), Honda CHA125 air-cooled motorcycle (GY6 engine); Market in the European Ⅰ plunger type carburetor motorcycle models on the intake pipe, no this structure, as long as you remove the air filter can (note: Ⅱ in Europe, the European Ⅲ motorcycle inlet pipe set have inlet joint). So the Ⅰ models, can be in after remove the air filter, with a proper size of plastic film cover the plunger type carburetor import (i.e., the connection parts air filter), with a small needle stabbed a pores among the plastic film, convenient for observation or try any gas emitted.

2. Slowly rotate the crankshaft according to the working direction of the engine, so that the radial surface of valve rocker arm R gradually leaves the camshaft lift, until the test cylinder piston is at the end of compression stroke position (as shown in FIG. 6), that is, the test cylinder inlet and exhaust valves are closed. The "T" mark on the flywheel rotor can be aligned with the sight hole mark on the left cover timing, or the cylinder cover can be opened to confirm the timing of the engine valve, so that the inlet and exhaust valves are closed. Then hold the bolt at the left end of the crankshaft with the special bushing hand to keep it still (two people cooperate with each other when conditions permit).

3. The throttle valve of carburetor is basically closed by adjusting the throttle screw of carburetor


4. Aim the rubber hose with ventilation pressure of 3 ~ 5kg/cm2 at the spark plug screw hole of cylinder cover, and try to keep air leakage at the joint.

5. According to the joint on the exhaust port and intake pipe of the cylinder cover (or the small hole in the middle of the plastic film at the entrance of the plunger carburetor), it can accurately determine which cylinder (referring to the multi-cylinder machine, which can be tested in turn according to the timing position) and which valve is not closed tightly and leak. This can be targeted to check valve, valve seat and according to the situation to repair or replace the relevant parts. It is important to note that before using this method, check that the engine timing and valve clearance are in normal condition to avoid miscalculation.

6. If no leakage is detected between valve or cylinder cover and cylinder body, dip the rubber vent hose end of engine crankcase into the prepared small water cup. If continuous bubbles appear, there is obvious leakage between cylinder and piston and ring. To verify the failure, remove the spark plug and pour a proper amount of viscous lubricating oil into the cylinder. After a few minutes, the oil slowly penetrates into the gap between the piston ring port, forming a thin film between the cylinder and the piston, and then test according to the above method. If there is no continuous air bubble in the crankcase vent hose, the cylinder and piston ring can be confirmed to have leakage fault.

Considering the difference between the hot and cold state of the engine and the seal leakage, it is suggested to test separately in the cold and hot state of the engine, so as to conduct comparison and avoid misjudgment.

Solutions to valve leakage:

1. Check whether the valve clearance is too small, leading to air leakage

2. Check whether the inlet valve, exhaust valve and valve seat are normal

3. Check whether the valve rod is deformed, bent, worn, carbonized, ablated or damaged.

4. Check whether the valve spring is back in position

5. Check whether the valve oil seal is normal

Grinding valve method:

Grinding valves is a technical job that many masters will not teach you because there is a lot of knowledge, technology, is not open, so you do not make money. However, in the spirit of our common learning purposes, to share with you, also hope you can understand.

Grinding valve first prepare an inlet valve, a tubing, valve sand (thickness), hand drill.

Now remove the cylinder head and valve seat. Inspection found that the inlet valve leakage caused by wear and tear, so we put the prepared inlet valve in the valve seat, with a pipe into the valve rod, a valve rod, a take over electric drill, put gas valve sand (coarse) at the door, and then start the hand electric drill rotating, it is best to slow, because of breaking them, fast is not good, grinding in 5 to 7 minutes, check whether the valve is good grinding. Then grind with valve sand (fine) for 3-5 minutes. In the valve replacement, must pay attention to the need for professional tools, need professional personnel to replace.

Examination method:

Put the intake valve and exhaust valve into the valve seat, then turn the cylinder head upside down and add water to the intake port to check whether the water leaks or whether the light leaks.


In the valve, be sure to clean the inside of the carbon, the piston top carbon clean. And replace the valve oil seal.