Engines family QG and QR, installed on Nissan Primera P12, are famous for their reliability, but the life of the cylinder head gasket is not endless. Operating the car in severe conditions, overheating or using low-quality antifreeze often leads to seal failure. Owners Nissan Primera It is important to recognize the symptoms of a malfunction in time to avoid costly repairs to the cylinder block.
The process of replacing the cylinder head gasket with QG18DE or QR20DE - this is a labor-intensive task that requires high precision and knowledge of the specifics of Japanese engines from the master. Errors when tightening bolts or cleaning surfaces can lead to re-burnout of the gasket after just a couple of thousand kilometers. In this article we will analyze in detail all stages of work, from diagnostics to final running-in.
Symptoms and diagnosis of malfunction
The first sign of problems with the cylinder head gasket is Nissan Primera P12 Often there is a change in the coolant level without visible external leaks. If you notice that you need to add antifreeze regularly and it's dry under the car, it's worth checking the oil for emulsion or bubbles in the expansion tank while the engine is running.
Another sure indicator is white smoke from the exhaust pipe, which has a sweetish odor and does not disappear after the engine warms up. In severe cases, the engine begins to operate unstably, stall, and compression in the cylinders drops due to coolant entering the combustion chambers. Compression and tightness cylinders are key parameters that need to be measured to confirm the diagnosis.
Sometimes the problem is disguised as a malfunction of the ignition system or injectors, which misleads inexperienced drivers. It is important to carry out a complete diagnosis, including checking the gases in the cooling system. If diagnostics confirm burnout, postpone repairs. shouldn't, since antifreeze getting into the oil destroys the crankshaft liners in a matter of hours.
Selection of components and tools
The quality of the cylinder head gasket directly affects the service life of the repair. For Nissan Primera It is strictly not recommended to install cheap analogues made of soft cardboard or asbestos. The optimal choice is metal gasket (multilayer steel), which can withstand high temperatures and pressure. Original parts from Nissan or proven brands like Victor Reinz or Elring will become a reliable guarantee.
In addition to the gasket itself, you will need a set of new cylinder head bolts, since they are stretchable and are not reusable. It is also worth replacing the valve cover gasket and manifolds immediately while the engine is disassembled. Don't forget to prepare new antifreeze and engine oil, and change the oil filter.
The tool kit should include a torque wrench, which is critical for proper tightening. Conventional ratchets will not provide the required torque and rotation angle. You will also need 10, 12, 14, 17, 19 and 21 mm sockets, spark plug wrenches, a pulley puller and preferably a hydraulic jack with a stand to support the cylinder block.
Preparing the vehicle and dismantling attachments
Before starting work, it is necessary to ensure free access to the engine. Remove the battery, air filter and throttle body. Disconnect all cooling system pipes, fuel hoses and electrical connectors. Be extremely careful with the sensors so as not to damage their wires. Coolant drain must be completed completely to prevent antifreeze from flowing into the spark plugs when removing the cylinder head.
Remove the intake and exhaust manifolds, first unscrewing all mounting nuts and bolts. Dismantling the throttle assembly and receiver is also necessary to access the block head. If you have a variable valve timing system installed CVTC, it must be carefully removed so as not to damage the mechanism.
Disconnect the accelerator cable and crankcase ventilation system. At this stage, it is important to label all wires and hoses to avoid confusion during assembly. Use plastic clips or electrical tape to number the connectors. Correct labeling will save you hours of time during the reassembly phase.
Unscrew the cylinder head bolts in a specific sequence, starting from the edges and moving towards the center to avoid deformation of the head. Remove the cylinder head by carefully lifting it up. If it is stuck, you can lightly pry it off with a wooden spatula, but under no circumstances use metal pry bars to avoid damaging the mating surfaces.
- Original Nissan
- Victor Reinz
- Elring
- Analogue of an unknown brand
Surface treatment and defect detection
After removing the cylinder head, it is necessary to thoroughly clean the mating surface of the cylinder block and the head itself. Use a wire brush and a special scraper, but be careful not to leave deep scratches. Any unevenness on the surface can cause re-burnout. Surface cleanliness - guarantee of tightness of the connection.
Be sure to check the plane of the block head for distortion. To do this, use a straight edge and feeler gauges. If the deviation exceeds the permissible values (usually 0.05-0.1 mm), the head must be sent for milling. Ignoring this step will result in the fact that even a new gasket will not provide a tight seal.
Check the condition of the valve guides and seats. Replace worn parts if necessary. It is also worth testing the valves for leaks by spilling kerosene into the combustion chambers. If the valves do not hold, they need to be ground in or replaced. Valve tightness affects the compression and stability of the engine.
What to do if the cylinder block is deformed?
If the cylinder block is curved, it must be ground on a special machine. In some cases, boring to fit the repair dimensions of the pistons is required, which significantly complicates and increases the cost of repairs.
Installing a new gasket and assembling the head
Install the new head gasket onto the cylinder block, making sure it is aligned correctly with the guide pins. Check for "Top" or "Up" marks on the gasket itself. Apply a small amount of sealant to the joints (for example, around the camshaft beds), if specified by the manufacturer's instructions, but do not overdo it so that excess does not get into the oil passages.
Reinstall the cylinder head and screw in new mounting bolts. The bolts are tightened in several stages using a torque wrench. Follow the strict tightening sequence specified in the service manual. Usually they first tighten it to a torque of 40 Nm, then turn it 90 degrees, and then another 90 degrees.
Install camshafts, pulleys and mechanism CVTC. It is important to set the valve timing according to the marks. An error of 1 tooth can lead to a collision of valves with pistons upon first start-up. Check the timing chain tension and condition of the dampers. Phase synchronization - a critical stage on which the life of the engine depends.
☑️ Checklist before installing the cylinder head
Final assembly and engine start
After installing the cylinder head, proceed to reassemble the attachment in reverse order. Connect all pipes, hoses, connectors and fuel lines. Install the air filter, throttle body and intake manifold. Add new oil and antifreeze, making sure the fluid level is correct.
Before the first start, check for leaks at the connection points. Turn the ignition on for a few seconds to allow the fuel pump to pump fuel into the system. Start the engine and let it idle. Monitor the engine temperature and oil level. If the temperature rises faster than usual, there may be air left in the system.
Check the operation of the cooling system for air pockets. If necessary, bleed the system by lifting the front of the car and opening the expansion tank cap. Pay attention to the operation of the stove in the cabin; it should blow hot air. No air locks will ensure efficient engine cooling.
When changing the oil for the first time after repairing the cylinder head, it is advisable to change it after 500-1000 km to remove possible wear products and sealant residues from the lubrication system.
Features of bolt tightening and nuances of QG and QR engines
Engines QG18DE and QR20DE have their own characteristics when tightening the cylinder head. The bolts on these motors are disposable, as they are made of a material that plastically deforms when tightened. Reusing such bolts is unacceptable, as they may not withstand loads and burst during operation.
The tightening procedure usually requires the use of the corner method. First, the bolts are tightened to a torque, then turned to a certain angle. This ensures uniform pressing of the gasket over the entire area. Errors in the tightening sequence can cause the head to become misaligned and cracks to appear in the casting.
Pay special attention to the camshaft bed area. This often requires the application of a special sealant at corner points. Use only sealants that are compatible with oil and antifreeze, such as silicone-based sealants. The wrong choice of sealant can lead to its dissolution and clogging of the oil pump.
Using a torque wrench and observing the rotation angles of the cylinder head bolts is not a recommendation, but a prerequisite for long-lasting repairs.
Possible complications and their prevention
Sometimes when removing the cylinder head, difficulties arise with jammed bolts. Do not use excessive force to avoid stripping the threads in the cylinder block. Use a penetrating lubricant and heat the bolts with a heat gun or blowtorch (be careful with plastic and wiring). If the bolt does break, you will need to install screw inserts or repair the threads.
Another problem may be damage to the pulleys or teeth of the timing belt/chain during dismantling. Always inspect these parts before installation. If there is even the slightest doubt about their integrity, replace them. Timing belt integrity - a guarantee that the engine will start and operate without failures.
In some cases, microcracks may be found on the cylinder block that are not visible to the naked eye. To identify them, capillary control or hydrotesting is used. If a crack is detected, the block requires complex repair or replacement. Don't take risks by installing a new gasket on a defective block.
⚠️ Attention: Never try to start the engine immediately after replacing the gasket without making sure that the timing is correctly installed and there are no leaks. This can lead to fatal consequences for the piston group.
⚠️ Attention: When working on the cooling system, remember that antifreeze is toxic. Collect waste fluid in a sealed container and dispose of it in accordance with environmental regulations.
| Parameter | Value for QG18DE | Value for QR20DE |
|---|---|---|
| Bolt tightening torque (stage 1) | 40 Nm | 40 Nm |
| Dovorot (stage 2) | 90 degrees | 90 degrees |
| Dovorot (stage 3) | 90 degrees | 90 degrees |
| Gasket type | Multilayer steel | Multilayer steel |
How to check the tightness after assembly?
The most reliable way is to leave the engine overnight and check the oil and antifreeze levels in the morning. You can also use a leak detector or test the system with compressed air.
⚠️ Attention: Never use sealant instead of a cylinder head gasket on a Nissan Primera P12 engine, as this is guaranteed to destroy the cooling and lubrication system.
FAQ: Frequently asked questions
Is it possible to drive a Nissan Primera P12 with a broken cylinder head gasket?
Driving is strictly not recommended. Antifreeze getting into the oil quickly damages the crankshaft bearings, and overheating can lead to deformation of the cylinder head or cracks in the cylinder block.
How long does it take to replace a head gasket?
For an experienced master, the work takes from 8 to 12 hours. If you do it for the first time, without experience and special tools, the process can take 1-2 days.
Do I need to replace the cylinder head bolts when replacing the gasket?
Yes, bolts on engines QG and QR are disposable. Their reuse is unacceptable due to plastic deformation, which reduces their strength.
What happens if you tighten the cylinder head bolts?
Overtightening can lead to thread breakage in the cylinder block, deformation of the head, or even a crack. This will require expensive repairs or replacement of components.