Engine G15, installed on Nissan Almera Classic, is a time-tested design, but requires periodic maintenance. One of the most critical procedures is checking and adjusting thermal clearances in the gas distribution mechanism. If you notice a characteristic metallic clatter, a change in the sound of the engine at idle, or a loss of power, most likely the problem lies in the valve mechanism.
Ignoring this procedure can lead to serious consequences, including burning out the valve seat or disrupting the valve timing. Unlike modern engines with hydraulic compensators, the motor G15 requires manual intervention. You need to know the exact values of the gaps and have a specialized tool on hand in order to do the job efficiently and without unnecessary service costs.
Why is it necessary to adjust valves?
The main reason for problems with valves is the natural wear of rubbing pairs and changes in the geometry of parts under the influence of high temperatures. During operation Nissan Almera Classic the metal expands and contracts, and constant shock loads gradually change the clearance between the rocker arm and the valve stem.
If the gap becomes too small, the valve does not have time to close completely when the engine heats up. This leads to loss of compression, overheating of the seat and, as a result, burnout of the valve. Too much clearance causes a characteristic knocking noise, which intensifies with increasing speed, and creates unnecessary stress on the camshaft cams, accelerating their wear.
The key factors influencing the need for adjustment are:
- 🔧 More than 60-80 thousand kilometers since the last adjustment.
- 🔧 Replacing the camshaft or rocker arms without first adjusting the gaps.
- 🔧 The appearance of extraneous noise in the upper part of the engine during operation.
Timely diagnostics allows you to avoid major repairs of the cylinder head. Please note that on the engine G15 there are no hydraulic compensators, so all gaps must be set mechanically using a feeler gauge.
⚠️ Attention: Neglecting regular checks of clearances on G15 series engines often leads to the valves not fitting tightly to the seats, which causes loss of compression and difficulty starting the engine in the cold season.
Tools and workplace preparation
For successful adjustment, you will need a set of specialized tools, which should be on hand before starting work. A standard set of keys will not help here, since high measurement accuracy is required. You will definitely need flat feeler gauges of different thicknesses to measure the existing gap.
In addition, you must have a torque wrench to tighten the cylinder head cover and camshaft pulley bolts. For ease of dismantling the units, a set of heads and extensions may be required. Don't forget to use clean rags and cleaner to remove dirt before starting disassembly.
You need to prepare the following tools:
- 🛠️ A set of flat probes (from 0.10 to 0.40 mm) with an accuracy of 0.05 mm.
- 🛠️ 10, 12, 14 and 17 mm sockets with ratchet and extension.
- 🛠️ Flat and Phillips screwdrivers for removing plugs.
Before starting work, the engine must cool down to ambient temperature. This is critically important, since all clearances are calculated on a “cold” engine. If you try to adjust the valves on a hot engine, the clearances will change as it cools and the procedure will go down the drain.
☑️ Preparation for adjustment
What to do if you don't have a torque wrench?
If you do not have a torque wrench, you can tighten the valve cover bolts by hand with moderate force, but always in several passes (in a crisscross pattern) to avoid distortion of the cover and subsequent oil leakage. However, to guarantee tightness, it is better to purchase or rent a tool.
Determining the order of operation of cylinders and phases
The main difficulty in adjustment lies in correctly determining the position of the crankshaft. You need to align the marks so that the piston of the first cylinder is at top dead center (TDC) at the end of the compression stroke. In this position, both valves (intake and exhaust) of the first cylinder are closed, which allows you to adjust their clearances.
To do this, you need to remove the plastic camshaft cover and rotate the crankshaft until the mark on the pulley matches the mark on the cylinder block. At the same time, check the position of the mark on the camshaft sprocket: it should coincide with the mark on the bearing housing.
The order of operation of the cylinders on the engine G15 - 1-3-4-2. This means that after adjusting the first cylinder, you rotate the crankshaft 180 degrees and adjust the next cylinder in order. It is important not to mix up the order, otherwise you will adjust the gaps on open valves, which will lead to improper operation of the motor.
- Flat styli
- Laser gap gauge
- Adjustment bolts without feeler gauge
- Other tool
Step-by-step instructions for adjusting gaps
The process begins with removing the cylinder head cover. Carefully unscrew the bolts, being careful not to damage the gasket. If the gasket is very stuck, use a plastic scraper to avoid scratching the metal surface. Clean the seat from any remaining oil and dirt.
Set the crankshaft to the TDC position of the first cylinder. Take a feeler gauge thick 0.15 mm for intake valves and 0.25 mm for graduation. Insert a feeler gauge between the rocker arm and the valve stem. The probe should enter with a little effort, but not get stuck or dangle loosely.
If the clearance is not correct, you need to loosen the lock nut on the adjusting bolt and rotate the bolt itself until the desired value is reached. After adjusting the gap, hold the bolt with a screwdriver and tighten the locknut with a torque wrench 15-20 Nm. Immediately check the gap with a feeler gauge again, as it may change when the nut is tightened.
Repeat the procedure for all cylinders, observing the order of operation. Remember to turn the crankshaft exactly half a turn (180 degrees) after each step. This ensures that you hit the correct valve timing for each piston.
| Valve type | Gap (cold) | Measurement location | Features |
|---|---|---|---|
| Inlet | 0.15 ± 0.03 mm |
Between the rocker arm and the rod | Adjustable with closed inlet valve |
| Outlet | 0.25 ± 0.03 mm |
Between the rocker arm and the rod | Adjustable with closed exhaust valve |
| Lock-nut | Tightening torque | 15-20 Nm | Tighten while holding the adjusting bolt |
When tightening the locknut, always hold the adjusting bolt with a screwdriver. If the bolt turns together with the nut, you will lose the set gap and will have to start the procedure again.
Common mistakes and how to avoid them
One of the most common mistakes is incorrect determination of TDC. Many mechanics focus only on the mark on the crankshaft pulley, forgetting to check the position of the camshaft. If the camshaft mark is off by one tooth on the chain, all your settings will be incorrect and the engine will run unstable.
Another mistake is using the wrong dipstick or running on a warm engine. Even a slight increase in metal temperature can change the reading. Also, do not use probes with worn edges, as they may give false readings.
Critical points to pay attention to:
- 🚫 Do not over-tighten the valve cover bolts, as this may cause the body to crack.
- 🚫 Do not ignore the condition of the oil seals when the cover is removed.
- 🚫 Do not use probes that have not been calibrated or have visible damage.
⚠️ Attention: If after adjustment you hear a knocking noise that does not disappear after a few minutes of engine operation, immediately stop the engine and check that the marks are set correctly. Incorrect timing can cause the piston to collide with the valves.
The main idea: The accuracy of setting the camshaft and crankshaft marks is 90% of success in adjusting the valves. Without correct phase matching, any gap adjustments are meaningless.
Checking the result and final assembly
Once all cylinder adjustments have been completed, the valve covers must be reinstalled. Apply fresh sealant to the corners of the lid if the old gasket has become loose or damaged. Tighten the bolts in a crisscross pattern to ensure an even fit.
Reassemble all the removed components in the reverse order: install the high-voltage wires, decorative engine cover and connect the battery. Start the engine and allow it to warm up to operating temperature. Listen to the sound of work: it should be smooth, without metallic clatter.
If everything is done correctly, the engine will run quietly and stably. Check for oil leaks from under the valve covers on a warm engine. If necessary, you can repeat the gap measurement on a cold engine after a week of operation for control.
⚠️ Warning: If after starting you hear an uneven knocking sound or the engine runs rough, do not continue driving. It is likely that one of the marks has become dislodged and will require re-disassembly and inspection.
Frequently asked questions from Nissan Almera Classic owners
How many times should valve clearances be checked?
It is recommended to check and, if necessary, adjust the clearances every 60,000 kilometers or every 3-4 years of operation, depending on the conditions of use of the vehicle.
Is it possible to adjust valves on a hot engine?
No, this is strictly prohibited. All engine clearance standards G15 indicated for cold conditions (approx. 20°C). When the engine is hot, the metal expands and the measurements will be incorrect.
What happens if the exhaust valve clearance is too small?
If the gap is too small, the valve will not close completely when heated. This will lead to loss of compression, overheating of the valve seat and burnout, which will require expensive repairs to the cylinder head.
Do I need to remove the camshaft for adjustment?
No, you don't need to remove the camshaft. Adjustment is made through the top with the valve cover removed using adjusting bolts and locknuts.
Which tool is best to use for measuring?
Use only high quality flat probes. Laser sensors can be inaccurate when operating rocker arms due to surface roughness. A standard set of probes is the most reliable option.