Diesel engine TD27Tinstalled on SUVs Nissan Terrano, is famous for its endurance and maintainability. However, the resource of this unit directly depends on the condition of the gas distribution mechanism. Over time, the clearances between the rocker arms and valve stems change, which leads to characteristic noise and loss of power.
Ignoring this problem can lead to burnt valves or poor valve timing. Owners Nissan Terrano it is necessary to understand that the adjustment procedure does not require complex special equipment, but it is time-consuming and requires care. Correctly exposed thermal clearances will ensure quiet operation of the engine and its stable start in cold weather.
Signs that valves need adjustment
The first and most obvious signal is a characteristic metallic knock at the top of the engine. This sound becomes louder during cold starts and may subside a little as it warms up, but does not go away completely. If you hear this rhythmic clatter, which intensifies as the speed increases, it means valve clearance exceeded the permissible values.
In addition to noise, problems with the timing belt are indicated by a decrease in the dynamic characteristics of the car. Engine TD27T may begin to “stupid” during acceleration, especially under load. There is also often an increase in fuel consumption and the appearance of black smoke from the exhaust pipe when changing gases. These symptoms indicate that the valves do not open or close completely, disrupting the combustion process.
- 🔊 The appearance of a clear metallic knock in the area cylinder heads
- 📉 Deterioration of throttle response and reduction of maximum speed
- 🌫️ Increased exhaust smoke and increased diesel fuel consumption
It is important to distinguish the knocking of valves from the knocking of hydraulic pushers or problems with the injection pump. On the engine TD27T There are no hydraulic pushers, so any metallic knock at the top of the engine is a reason to check the clearances. You shouldn’t put off visiting a mechanic or self-diagnosis, as ignoring the problem will lead to costly repairs to the cylinder head.
⚠️ Warning: If the knocking becomes very loud and can be heard even with the windows closed, driving such a vehicle may cause the valve to “knock off” the seat or break the rocker arm. In this case, stop and call a tow truck.
Necessary tools and preparation
To do the job well, you will need a set of standard tools and special probes. Pay special attention gap gauges, they must be smooth and free of burrs. You will also need a key to rotate the crankshaft, since turning the engine by the generator pulley or timing belt is extremely inconvenient and risky.
Be sure to have a clean rag and a can of carburetor or diesel cleaner ready. Before starting work, it is necessary to remove the valve cover, which may be heavily contaminated with oil and dirt. If the lid is stuck, do not hit it with a hammer; carefully pry it off with a flat-head screwdriver so as not to damage the gasket and the lid itself.
- 🛠️ Set of open-end and spanner wrenches (mainly 10, 12, 14 mm)
- 📏 Set of probes with thickness from 0.10 to 0.40 mm
- 🔧 Screwdrivers (flat and Phillips) for dismantling parts
- 🧴 Cleaner and rags for degreasing the surface
It is better to carry out work on a warm engine, but not hot. The ideal temperature is around 40-50 degrees Celsius. On a cold engine, the metal is compressed, and on a too hot engine, it expands, which can cause an error in measurement. Nissan Terrano with diesel TD27T has a cast iron block that retains heat for a long time, so let the engine cool down a little after the trip.
- Less than 10,000 km
- 10-20 thousand km
- 20-30 thousand km
- More than 30 thousand km/I don’t remember
The order of rotation of the crankshaft and the determination of TDC
The adjustment process requires consistency. The engine must be turned clockwise using a special wrench on the crankshaft pulley. It is important to understand that top dead center (TDC) - this is the position when the piston of the first cylinder is at the very top of the compression stroke. Only in this position are both valves (inlet and outlet) closed.
There are marks on the crankshaft pulley cover and on the engine housing. The combination of these marks indicates TDC. However, one mark is not enough, since the crankshaft makes two revolutions in one working cycle. Therefore, after aligning the marks, you need to check that the camshaft is in the position where the cams of the first cylinder look up (in different directions from the rocker arms).
If the marks match, but the cams are pointing down, then you are at TDC of the exhaust stroke. In this case, you need to make another full revolution of the crankshaft. A mistake of half a turn will result in you adjusting valves that are open, rendering the entire procedure pointless.
☑️ Checking the crankshaft position
Technical characteristics of clearances and table of values
Engine TD27T has strict requirements for thermal clearances. These values are not recommendations, but are specified in the technical documentation of the manufacturer. A deviation of even hundredths of a millimeter can change the operating characteristics of the motor. Intake valves operate in less severe temperature conditions, so their clearance is smaller than that of the exhaust valves.
The exhaust valve heats up significantly more as hot gases escape through it. When heated, the valve stem elongates, and if the clearance is not left sufficient, the valve will not be able to close completely. This will cause the edge of the plate to burn out and loss of compression. This is why the clearance is always larger for exhaust valves.
| Parameter | Cold engine | Warm engine | Note |
|---|---|---|---|
| Inlet valve | 0.25 mm | 0.30 mm | The gap is smaller because the heating is lower |
| Exhaust valve | 0.35 mm | 0.40 mm | Critical due to high temperatures |
| Measurement accuracy | ±0.02 mm | ±0.02 mm | Use quality probes |
The table shows standard values for most modifications TD27T. However, if the engine has undergone major repairs or has a mileage of more than 300 thousand kilometers, some experts recommend slightly increasing the clearances by 0.02-0.03 mm to compensate for wear of the seats and pushers. But this must be done with caution so as not to worsen the filling of the cylinders.
For the TD27T engine, it is critical to maintain the difference between the intake and exhaust valve clearances, as this directly affects the combustion chamber temperature and engine life.
Step-by-step adjustment instructions
Begin adjustment from the first cylinder when the crankshaft is at TDC on the compression stroke. Loosen the adjusting bolt locknut on the intake rocker arm. Insert a feeler gauge of the required thickness (0.25 mm for intake) between the end of the valve stem and the rocker arm adjusting bolt.
Then, holding the adjusting bolt from turning with a wrench, tighten the locknut. When tightening the locknut, the bolt may rotate, causing the clearance to change. Therefore, the tightening technique needs to be worked out: lightly hold the bolt, tighten the nut, then release the bolt and check the gap again with a feeler gauge. The dipstick should pass with slight effort, but not dangle.
- 🔧 Loosen the locknut 1-2 turns
- 📏 Insert the feeler gauge and adjust the bolt to the desired tension
- 🔒 Tighten the locknut while controlling the position of the bolt
- ✅ Check the gap again after tightening
After adjusting the first valve, move on to the exhaust valve. The gap here should be 0.35 mm (when cold). The procedure is identical. After completing work on the first cylinder, rotate the crankshaft 180 degrees (half a turn) clockwise. This will take you to adjusting the valves on the third cylinder.
Sequence of work on cylinders TD27T the following: 1, 3, 4, 2. This is the standard operating order of the engine. Skipping any step or incorrect rotation sequence will result in you adjusting open valves. Remember: Always check that both valves are closed before adjusting a specific cylinder.
What should I do if the adjusting bolt rotates along with the nut?
Sometimes the thread on a bolt breaks or the nut gets stuck. In this case, you need to hold the bolt with two keys or use a special tool. If the bolt comes out completely, the rocker arm may need to be replaced.
Features of working with turbocharging
Engine TD27T It is equipped with a turbocharger, which imposes additional requirements on the cleanliness and condition of parts. The turbine removes some of the energy from the exhaust gases, so the exhaust valves operate under extreme conditions. Any error in the adjustment of the exhaust valves can lead to overheating of the exhaust manifold and turbocharger.
When adjusting, do not allow dirt to get into the valve area. Fine dust can get on the guide bushings and cause them to wear out quickly. Before installing the valve cover, be sure to blow out the passages with compressed air and wipe all surfaces. Also check the condition of the cover gasket; if it is torn or has lost elasticity, it needs to be replaced.
Pay attention to the condition of the rockers (rocker arms). On high mileage engines they may develop wear at the point of contact with the valve. If the hole is deep, the adjustment may not give the desired result, since the bolt will rest against the hole. In this case, it is recommended to replace the rocker arm or grind the surface (if the design allows).
⚠️ Attention: Never adjust the valves while the turbine is still hot after a long trip. A sharp temperature change during cooling can deform the parts of the block head, which will lead to uneven gaps.
Checking the result and final assembly
After all valves have been adjusted, proper operation must be checked. Manually rotate the crankshaft two full turns and return to TDC of the first cylinder. Make sure that the gaps have not changed and the feeler gauges pass the same way as during the first check. If the gap has changed, it means that the nuts were not tightened securely enough or the threads have “sagged.”
Reinstall the valve cover gasket. Apply a small amount of sealant to the corners of the cover and at the junction with the block head, where oil often leaks. Install the cover and tighten the bolts in a crisscross pattern to ensure an even seal. Avoid overtightening, as the aluminum cylinder head may crack and the gasket will be squeezed out.
Start the engine and listen to its operation. The sound should be smooth, without the characteristic metallic clatter. Let the engine idle for 5-10 minutes. If the noise appears after warming up, you may have overtightened the gaps or made a mistake when calculating the temperature correction.
Apply a light amount of oil to the threads before final tightening all valve cover bolts. This will help prevent the bolts from sticking in the future and will make it easier to remove the cover the next time you make adjustments.
Frequent errors during adjustment
One of the most common mistakes is incorrect determination of TDC. Many beginners focus only on the marks on the pulley, forgetting to check the position of the camshaft cams. This causes the valves to be adjusted, which are open, rendering the procedure useless. Always check that both valves on the first cylinder are closed.
Another mistake is using incorrectly selected probes. If the dipstick is bent or has burrs, the readings will be incorrect. Also, you should not use a stylus set that has significant wear. Thin feeler gauges often bend, while thick ones may not fit into the gap, creating the illusion of the correct gap.
- ❌ Adjustment on too hot or too cold engine
- ❌ Ignoring the order of cylinders (1-3-4-2)
- ❌ Insufficient tightening of locknuts after adjustment
- ❌ Using damaged or dirty probes
If you are not confident in your abilities, it is better to entrust this work to professionals. An error in valve adjustment can cost much more than the cost of a service. However, with knowledge and patience, you can save money and extend the life of your Nissan Terrano.
The quality of valve adjustment directly affects the environmental friendliness of the exhaust and fuel consumption, so this procedure cannot be neglected even in the absence of obvious signs of malfunction.
How often should the valves on the TD27T be adjusted?
The manufacturer recommends adjustments every 20-30 thousand kilometers. However, if you hear knocking sooner, do it immediately. If low-quality fuel or oil is used, the interval may be shortened.
Is it possible to adjust valves on a hot engine?
Technically it is possible, but the gap values should be different (usually 0.05 mm more). However, for precise tuning, it is better to wait until the engine cools down to 40-50 degrees to avoid errors due to thermal expansion of the metal.
What happens if the gap is too small?
The valve will not be able to close completely. This will lead to loss of compression, burnout of the valve disc, decreased power and increased fuel consumption. In extreme cases, the valve may become stuck.
Do I need to remove the timing belt for adjustment?
No, adjusting the valves does not require removing the timing belt. It is enough to remove the valve cover and have access to the adjusting bolts. The belt should only be removed when replacing it or repairing the camshaft.
How do you know if the gap is set correctly?
The feeler gauge should pass between the rocker arm and the valve stem with noticeable but not strong resistance. It should not dangle, but it should not get stuck with great force. If the probe enters too easily or does not enter at all, you need to reconfigure.