Nissan timing chain replacement
Replacing the timing chain was once a rarely done job on import vehicles. Usually, rusty bodywork or other mechanical issues sent the vehicle to the scrapyard long before the chain stretched or broke.
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Now, with vehicles that last longer and rack up more miles, replacing the timing chain on some models is becoming a much more common occurrence.
What is there to blame? Some say it’s a mileage and longevity issue. Some say it’s because the chains have gotten longer and have more links to wear. Whatever the reason, your store has probably seen a slight increase in this type of service.
The Nissan VQ V6 aluminum DOHC requires a decent amount of disassembly to service the timing chains. Valve covers, front cover, and other components should be removed. When replacing the timing chain, do the entire job and replace the tensioner, guides, and in some cases, sprockets. On higher mileage engines, replacement of variable valve timing phasers is recommended. But, on all jobs, the water pump must be replaced.
The VQ V6 has three oil chain tensioners. The main chain has one tensioner and two secondary chain tensioners. When replacing the main chain tensioner, make sure the mating surfaces are clean and free of damage and debris. The secondary chain tensioners require the removal of the intermediate covers and camshaft bearing caps.
Replace gaskets and sealants that fit into the grooves of the caps and covers. Failure to complete this step can result in internal leaks which can drain the tensioner and phaser. Leaks can cause noise when starting because oil fills the tensioner and phaser.
On variable valve timing engines, you will need to remove the oil control solenoids. Always use a new gasket and gaskets on the valves.
The condition of the guides can also cause instability of the timing system during start-up. Lack of oil can melt the guides. Also, if the tensioner sags when starting, the chain whip can cause the bar to break.
The main timing chain uses an inverted tooth design. It has intertwined links held together by pins. Instead of a roller making contact with the teeth of the sprocket, the links make contact. Reverse tooth chains are generally quieter than roller chains.
The shape of the links of a reverse toothed timing chain is specific to sprockets. The Nissan links of this type of chain engage in specific areas of the teeth.
If a replacement timing chain does not match the original link profile, it will cause more noise. In addition, an incorrect profile can affect chain stability and cause chain whipping. It is the root cause of premature wear and stretching. Some chain kits include new sprockets and camshaft phase shifters that are compatible with the new chain.
The traditional configuration of a water pump is to rotate it by the accessory belt drive system. It is simple and efficient and allows maintenance if the water pump fails. But, its only drawback is the force that the belt exerts on the bearing and the seals of the pump.
One solution is to have the timing chain feed the water pump. Since the chain has teeth that turn the pump, less force is exerted on the shaft, which theoretically allows it to last longer. But, since the pump is part of the engine valve control, the maintenance of the pump is difficult.
In fact, at the top of the list of the most difficult to replace water pumps are those found in Nissan’s VQ series V6 engines. The pump is driven by the timing chain and is nestled in the engine block. Whether the motor is mounted transversely or longitudinally, the work requires a significant amount of labor.
The first sign of water pump bearing failure will be a coolant leak from a hole on the block near the A / C bracket. This hole leads to the pump drain hole. The hole is between two gaskets that separate the oil on one side and the coolant on the other. If the outer O-ring fails, there will be a coolant leak in the area of ââthe front cover connected to the oil pan. It could mimic a head gasket leak.
When replacing the pump, pay close attention to the O-rings. These should be lubricated with oil or coolant. The rings should be able to seal and move small amounts as the block heats and cools. Do not use silicone or other sealants – this could block the drain hole in the block.