Engine Nissan QG15DE, installed on the model Sunny (and its analogue Almera), has earned a reputation as a reliable unit, but its service life directly depends on the condition of the gas distribution mechanism. Many owners are faced with the need to replace the timing belt, but not everyone understands how critical the accuracy of the alignment of the marks is. An error of even one tooth can lead to a collision between the valves and the pistons, which will be fatal to the engine.
In this article we will analyze in detail the process of placing marks on the crankshaft and camshafts. You will learn how to properly crank the engine, what nuances the system has CVTCS and how to avoid common mistakes made during DIY repairs. Exact adherence to technology is the key to the long life of your car.
Preparing the engine for marking
Before starting work, it is necessary to ensure access to the timing belt. To do this, you will need to remove the plastic engine casing, unscrew the alternator belt and dismantle the right front wheel and fender liner. This is standard procedure, but it is important to ensure that the vehicle is securely supported by jack stands and not just a jack.
Pay special attention to cleaning the work area. Sand and dirt that gets inside the mechanism when the covers are removed can cause premature wear of the new belt. Use compressed air or a brush to remove deposits from gears and tensioners. Cleanliness in the engine compartment is not just aesthetics, but a technical safety requirement.
The next step is to remove the upper and lower timing belt covers. They are usually mounted on bolts of different sizes. Remember or photograph the location of the bolts so as not to mix them up during assembly. Pay attention to the condition of the crankshaft seals - if they are leaking, replacement must be made immediately.
⚠️ Attention: Do not attempt to crank the engine by the crankshaft pulley if the timing belt is removed or loosened. This will lead to irregular valve timing and possible damage to the valves.
Setting the top dead center (TDC)
The key point of the entire operation is setting the piston of the first cylinder to the top dead center of the compression stroke. To do this, use the head on 19 mm (sometimes 21 mm depending on the year of manufacture) and rotate the crankshaft clockwise. The rotation should be smooth, without jerking, so as not to damage the gears.
The reference point is the mark on the crankshaft pulley and the notch on the timing cover. They should match perfectly. At the same time, check the position of the marks on the camshafts. On the gears QG15 there are special notches that should look straight up or coincide with the plane of the cylinder head.
If the marks do not match, do not under any circumstances try to tighten the belt to “close” the gap. This is a recipe for failure. You need to loosen the tensioner, remove the belt, manually adjust the crankshaft and camshafts to the desired position, and then put the belt back on. Accuracy is most important here.
- ✅ Check that the mark on the crankshaft pulley matches the mark on the oil pump.
- ✅ Make sure that the marks on the camshaft gears are in the same plane.
- ✅ Install the camshaft retainer if it is provided for in the design of your kit.
- Standard set of keys
- Special fasteners
- Homemade devices
- I contact the service
CVTCS system and its features on QG15
Engine QG15DE equipped with a variable valve timing system CVTCS (Continuous Valve Timing Control System). This system operates on the intake camshaft only and is controlled via a hydraulic coupling. When replacing a belt, it is important to consider that the coupling may be in an arbitrary position, which makes it difficult to set marks.
If you simply align the marks on the gear without fixing the position of the clutch, the phases may be out of order after starting the engine. This manifests itself in unstable idle speed, loss of power and increased fuel consumption. For correct installation, it is necessary to fix the coupling in its extreme position.
There is a special locking method: you need to screw the bolt into the hole on the coupling cover or use a special lock that is inserted into the gear and the block head. If there is no lock, some craftsmen use the “feel” method, turning the shaft counterclockwise until it stops, but this requires experience and caution.
⚠️ Attention: If equipped with a CVTCS system, the mark on the gear may not match the mark on the cover until the belt is installed and tensioned. This is normal, but requires strict adherence to the procedure.
☑️Checking CVTCS phases
Table of matches of labels and parameters
For clarity, we provide a summary table that will help you control the installation process. Remember that even a slight deviation in millimeters can lead to serious consequences. Always refer to this table at every step.
| Component | Mark position | Checkpoint | Tolerance |
|---|---|---|---|
| Crankshaft pulley | Top point | Risk on the lid | 0 mm |
| Intake camshaft gear | Mark up | Cylinder head plane | ±1 mm |
| Exhaust camshaft gear | Mark up | Cylinder head plane | ±1 mm |
| CVTCS coupling | Anti-clockwise emphasis | Bolt fixation | No backlash |
Tensioning procedure and final check
After all the marks are set and the belt is put on all the gears, the tensioning stage begins. Tensioner roller on engine QG15 usually has a hydraulic or spring mechanism. If the roller is hydraulic, it must first be compressed and secured with a pin, and then installed in place and the pin removed after tensioning.
It is important to crank the engine by hand at least two full turns (720 degrees). This is necessary to make sure that the belt has not jumped off and all marks coincide again at TDC. If after two revolutions the marks have shifted, it means you made a mistake during installation or the belt is stretched (if an old belt is used, which is unacceptable).
After checking the tension, finally tighten the crankshaft pulley bolt to the torque specified in the instructions (usually about 100-120 Nm). Don't forget to also check the tension of the alternator belt and adjust it if necessary. The sound of the engine should be smooth, without extraneous noise.
- ✅ Use a torque wrench to tighten critical components.
- ✅ Make sure that the tensioner roller rotates freely without jamming.
- ✅ Check that there are no belt distortions on the gears.
What if the labels don't match after scrolling?
This means that the valve timing is disrupted. The belt must be removed and the alignment procedure repeated, paying particular attention to the CVTCS system. In the worst case scenario, this could indicate a stretched belt or worn gears that require replacement.
The final check by two revolutions of the crankshaft is a mandatory step, which saves time and money on subsequent repairs.
Common mistakes and their consequences
A common mistake is to ignore the system CVTCS. Many craftsmen simply align the marks on the gears without locking the clutch firmly. As a result, the engine starts, but is unstable, stalls at idle, or loses dynamics. Correcting this error requires removing the gear and re-adjusting it.
Another problem is incorrect belt tension. Too little tension leads to slippage and phase failure, and too much tension leads to rapid wear of the roller bearings and tensioner. The engine begins to make noise, vibrations appear, and the service life of parts drops sharply.
It is also worth mentioning errors when assembling protective covers. If the timing covers are installed crookedly or not completely, they can hit the belt, causing it to fray. This is a silent but very dangerous problem that may only appear after several thousand kilometers.
⚠️ Attention: Using non-original timing belts with the wrong length or stiffness is a common cause of phase failure on motors. Nissan. Always check the part number before purchasing.
Before installing a new belt, be sure to clean the gears of old grease and dirt, otherwise the belt may slip during the first start.
Diagnostics after timing belt replacement
After completing all work and starting the engine, it is necessary to conduct a thorough diagnosis. First of all, listen to the engine. The sound should be smooth, without clicking or knocking. If you hear metal rubbing or whistling sounds, stop the engine immediately and check the tension.
Check the system operation CVTCS using a diagnostic scanner. The phase advance angle parameters must correspond to the norm at different speeds. If the scanner shows a phase error or “floating” values, it means that the installation was performed incorrectly.
Also pay attention to fuel consumption and acceleration dynamics. If the car starts to drive worse or the consumption has increased, the valve timing may be shifted. In this case, the tags will need to be checked again. Don't forget that the engine QG15DE very sensitive to timing settings.
- ✅ Check for errors in the engine control unit (ECU).
- ✅ Warm up the engine to operating temperature and check the speed stability.
- ✅ Check the operation of the cooling system and the absence of leaks.
How to check the operation of CVTCS without a scanner?
With the engine warm, press the gas hard. If the system is working, you will feel a characteristic pickup. If the engine stalls or stalls when the throttle is opened suddenly, the system may be faulty or incorrectly configured.
FAQ: Frequently asked questions
Is it necessary to change the timing belt on QG15 according to the regulations?
Yes, the scheduled replacement period is 90,000 km or 5 years, whichever comes first. However, if there are signs of wear (cracks, delamination), replacement should be made earlier.
Is it possible to crank the engine using the camshaft gear?
Absolutely not. This can lead to damage to the CVTCS phase regulator and disruption of the timing mechanism. Rotate the engine only by the crankshaft pulley.
What happens if the camshaft gears are swapped?
The engine will not start. The intake and exhaust shafts have different cam shapes and different mark positions. Trying to start will cause the valves to hit the pistons.
Do I need to change the tension pulley when replacing the belt?
It is highly recommended to change the roller and water pump at the same time as the belt. This will save money and time in the future, since access to these components will require re-disassembling the timing belt.
How can you tell if your CVTCS system is faulty?
The main symptoms are: unstable idle speed, loss of power at low speeds, increased fuel consumption and error P0011 or P0021 on the diagnostic scanner.