How to do special sounding diesel engine, X

How to do special sounding diesel engine, X

The abnormal sound of the special-purpose diesel engine mainly includes the piston knocking, the piston head knocking, the piston disengaging, the piston rubbing the "shoulder arm" sounding, the piston pin ringing, the connecting rod bearing <small tile> ringing, the crankshaft bearing ( Large tiles) ring, air leakage, valve sound, tappet ring and timing gear ring and so on.

● The piston knocks

If the gap between the piston skirt and the cylinder sleeve is too large, when the diesel engine is idling, a clear and rhythmic percussive sound will be emitted in the upper part of the cylinder block. The gasoline engine is 'boosted'. The diesel engine is "just" sound. The piston has a small diameter and the sound is crisp. The piston has a large diameter and the knocking sound is heavy.

Obvious low speed, middle and high speed sound disappears. The low-speed flapping throttle has a 'click and bang' sound. When the water temperature of the diesel engine is lower than 40 degrees Celsius, the sound is weakened or disappears as the temperature rises, and the severe piston knocking sound is not weakened at any temperature. Listening and listening are more obvious than virtual hearing. When the single-cylinder cuts off the oil, the sound is weakened or disappears. The cylinder whose sound is changed is the cylinder that the piston knocked.

False hearing: It means standing in front of the engine and listening to noise through the air.

Listening: Use a hollow tube to insert into the crankcase and hear the piston, crankshaft and connecting rod directly.

Really hear: Use a metal rod or a long handle to hit the body of the diesel engine, rely on the vibration of the body to hear abnormal sound.

Oil breakage method: Loosen the high pressure oil pipe coupling nut of the high pressure cylinder to stop the oil supply.

● Piston off

Piston decapping refers to the breakage of the head and skirt from the oil ring groove of the piston. Generally, the piston head stays at the uppermost part of the cylinder. The skirt still moves up and down with the connecting rod and collides with the piston head. .

Above the diesel engine, you can virtually hear a loud 'bang' sound, and all the speeds will sound. The high speed sound will increase; the cylinder head of the engine will be falsely heard, and the sound will be heard; the sound will not change after the oil is cut off; When it is not working, the diesel engine is started after the injector is removed. The fault cylinder has no compressed air, and the abnormal noise of the cylinder is very large.

When there is a failure of the piston to lift off and there is no maintenance condition, the cylinder head can be removed and the piston head can be pressed down to the point, then the crankshaft can be quickly cranked to push it out, and then the cylinder head is installed and the cylinder is closed. The push rods and the two valves are pushed out so that the intake and exhaust valves of the cylinder are always closed, so that the cylinder does not work at all. After such processing, the diesel engine operates with one cylinder missing.

● The piston hits the cylinder shoulder

In repairing a diesel engine, if the cylinder shoulder is not inspected (where the uppermost part of the cylinder liner is not rubbed by the piston ring and a step is formed, this step is called cylinder shoulder), the newly replaced piston ring is not chamfered. During the test run, a crisp 'click' sound will be heard, and it will ring at any speed; the sound in the upper part of the diesel engine block will be heard, and the actual sound will be obvious; when the oil is cut off, the sound will not change; the diesel engine will have Jitter feeling.

● Piston pin

The piston pin and the connecting rod bush were improperly repaired due to the wear, so that the clearance was too large, and the diesel engine operated at a slightly higher idle speed. A more clear and rhythmic percussive sound was emitted in the upper part of the cylinder than the piston knocked.

Idle noise appears, and the idle speed is slightly higher; when the oil is cut off, the sound of the malfunctioning cylinder becomes louder and the frequency of tapping is faster; when the speed is medium, it weakens and disappears completely at high speed.

Severe piston pin sounds, the sound is noticeable at low speed, and does not disappear at medium speed: the sound is more pronounced at mid-speed refuelling, and the abnormal sound disappears when the oil is cut off.

● Connecting rod bearing ring

Connecting rod bearings and connecting rod journals are not suitable for reasons such as wear or improper maintenance, so that their clearance is too large. When the diesel engine is running at a medium speed, a short metal percussion sound can be heard in the lower part of the cylinder.

Can't hear it at low speed, gradually becomes more obvious with the increase of speed, medium speed is the most obvious, and high speed has weakened or disappeared: The medium speed shaking throttle has obvious “呜, 嗒, 嗒, 呜 声” sound, in the lower part of the cylinder Listening was particularly prominent; the moment the diesel engine was shut down for ten minutes and then started, the noise was even more pronounced: When the single-cylinder was shut off to the faulty cylinder, the sound would disappear, and severe bearing ringing would only weaken.

● crankshaft bearing ring

The clearance between the crankshaft bearing and the crankshaft journal is too large, causing the journal to collide with the bearing. The sound appears at medium speed, high speed is obvious, and there is always noise in the middle and high speed range: the weight of the bearing is heavier than the connecting rod; the noise increases with the increase of the load, and the medium and high-speed shaking of the throttle is the most obvious: after multiple bearings are seriously damaged, Oil pressure will drop significantly.

The high-speed real listening or the high-speed shaking of the oil valve is very obvious; the sound of the diesel engine stopping for more than 10 minutes and then starting is especially prominent; the two-cylinder single-cylinder oil shut-off sound will disappear, and the other cylinders will have fault bearing at the same time. The sound of oil cut off from the adjacent two cylinders will disappear.

● cylinder leakage

Compressed gas in the cylinder passes through an unsealed piston, valve, cylinder pad, injector hole, and spark plug hole as if it were leaking. Here is the sound of air leakage caused by the piston not sealing and the cylinder pad damaged.

Pistons and cylinder liners are slightly leaky. When running at low speeds, they can hear a "click" sound, the "Bonbon" sound in the middle speed, the high speed attenuation, the pulsating smoke in the crankcase vent, and the exhaust. A large amount of blue smoke is emitted; if the cylinder head gasket between adjacent two cylinders is damaged, the diesel engine will appear "tempered" and "blasted"; the cylinder head gasket is damaged and communicates with the outside of the cylinder, and the outside of the diesel engine can virtually hear "Bonbon" “Sound; If the damaged cylinder head pad is in the water jacket position, it will spray white steam outside: If the damaged cylinder pad is in the oil hole position, it will spray oil out.

The noise of the faulty cylinder will be weakened or disappeared when the single-cylinder is shut off, and the pulsating smoke of the crankcase vent will be reduced; if most cylinders leak, the vent will continue to smoke, and the abnormal noise of the single-cylinder cut off oil will not disappear. difficult.

● Valve and tappet ring

The valve and its drive mechanism have large clearances. When the diesel engine is at a low speed, a clear and rhythmic stroke can be heard in the valve room as a valve sound; if a similar sound is heard in the tappet chamber, Called tappet ring. Their common feature is that the sound of breaking the oil on a cylinder-by-cylinder basis does not change, and only when the oil is cut off, the knocking frequency becomes slower.

● Timing gear ring

The valve mechanism of a medium-sized diesel engine or above is generally driven by a timing gear, and a light automobile is generally driven by a timing gear or a timing chain. Due to wear, damage, looseness, excessive or small axial clearance of the camshaft, improper use, etc., the gears and clearances of the timing gear are not normal, so that gear teeth and ringing occur; the rotational speed is unstable and the sound is pronounced; No change after the sound.

The sound of idling sounds, and the idling speed is slightly higher; in the gear room, there is false hearing, and there is a "click" or "click." Timing chain is "click"; if the timing gear teeth and clearance is too small, there will be "whistling" sound at medium speed.

● loose flywheel

When the diesel engine is unstable or rapidly accelerating, there is a loud “dangling, jingling” sound at the flywheel; when the car starts, there will be a feeling of clutch trembling; when the oil is cut off, there is a “creak” sound; after the diesel engine goes out, Turning the flywheel by hand will feel loose.

● Foreign objects in the combustion chamber

For non-flat-topped piston combustion chambers (such as spherical, shallow-circular, etc.), it is easy to leave screws or nuts on top of the piston during maintenance, and a clear knocking sound can be heard during the diesel test run.

The sound is present at any rotational speed; cylinder-by-cylinder shut-off, no change in sound, and each cylinder is working properly; the most obvious in the cylinder head is listening, which is more obvious in the upper part of the diesel than in the lower part. Check valve clearance is normal.

Abnormal sound and speed have nothing to do with the oil cut off does not change, check the valve clearance in the sound of the location, are normal, should consider foreign matter in the cylinder.

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