Below we list the consequences of an incorrectly set clearance in the valve actuator.
Too small thermal gap
The valves do not fit tightly to the seats, very hot exhaust valves cannot transfer heat to the seat facets because of this. Then the valves and their seats burn out, because hot combustion products pass through the latter. In milder cases, the valves warp. the seal is damaged, as a result of which the seat will soon burn out. Compression is reduced, the engine loses power, runs worse and consumes more fuel.
Too large thermal gap
The valves open a little later than usual: the cylinders fill up worse, the engine does not develop full power. The wear at the camshaft and at the adjusting washer, folded at the top into the cup pusher, becomes greater. This is evidenced by a lot of noise coming from the valves.
Checking the thermal gap
You can check the thermal gap yourself. The engine must be warm to check (coolant temperature is 35 degrees Celsius). This is achieved after idling the engine for about 5 minutes. When reinstalling the valve cover, a new seal must be inserted to avoid leaks (three details).
- Remove valve cover.
- Measurements are taken simultaneously at the inlet and outlet valves of the cylinder. The valves must be free.
- Turn the crankshaft of the engine by hand until the tips of both cams on the first cylinder point upwards on the camshaft.
- First try to insert between the camshaft and the pusher cup a piece of feeler gauge corresponding to the upper tolerance value (see table below), then insert thinner sheets equal to 0.05 mm.
- The feeler gauge for a smaller value must be inserted with slight resistance, otherwise the valve clearance is too small
- Less commonly, there is too much clearance, then you can insert a stylus sheet that is thicker than the specified upper tolerance limit.
- Record the measured value.
- In accordance with the order of work, the 3rd cylinder is then checked (1-3-4-2).
- To do this, the crankshaft of the engine must be turned another 1/2 turn. Now at the 3rd cylinder, both camshaft cams should look up. You can measure at cylinder 3.
- Check the rest of the cylinders in the same way. To do this, turn the engine crankshaft 1 2 turns further.
Correctly set valve clearance
The table shows the values within which the valve play must be at a coolant temperature of 35 degrees Celsius.
The figure shows a feeler gauge that is inserted at the 4th cylinder to measure the valve clearance. The length of the inlet valves should be 0.20-0.30 mm, and the exhaust valves should be 0.40-0.50 mm. These parameters are given for a warm engine. To measure the valve play of a cylinder, both camshaft lobes must look outward (mirror inverted), as the arrows show.
Suction diesel and turbodiesel engine | Inlet valve | Exhaust valve |
Valve play on a warm engine | 0.20-0.30mm | 0.40-0.50 mm |
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