Potential rod knock???

[Wertbe]

My '98 Pathfinder has recently started making an alarming sounding racket, from the lower end of the engine. As the title suggests, my thoughts go towards worst case scenario and say its a rod knock in its early stages. I've recorded a video of it, which is the worse the noise has been so far, and iirc the engine was at full operating temp. It's not quite as loud or deep as bad rod knock is, but that's why I say it could be in the early stages. It could be attributed to piston slap, but as far as I know, that sound would go away when it warms up, plus this sound has been happening for maybe 3 weeks now, as opposed to the 3 years that I've owned it.

 

The youtube channel 'Auto can' has a series of videos diagnosing a vg33e knocking sound, and it turned out to be the keyways on the timing belt sprocket and crankshaft being very deformed, allowing the key to rattle around when running. I don't know if I'd rather have that than rod knock but it could be that as well considering how relatively quiet the noise is? One additional thought I had about this was that according to the maintenance records I have, the timing belt was done at 103k miles, and it now stands at 170k miles. Technically less than Nissan says to replace the belt, but not out of the possibility it needs replacing and could be contributing to the noise, right?

 

I should also mention that I went on a quick drive before posting this, getting it to operating temp for around 15 minutes. Neither when it was idling cold nor after the drive did the noise come up, it sounded just as it did before the concern arose. I don't know what that means but probably good to know. 

 

This car was very nicely garage kept and maintained for most of it's life before I had it, and while sadly it did experience a decently big front end collision (that didn't immediately affect any mechanical components), I have been very on top of oil changes and other maintenance items, so it's very frustrating to see the engine potentially going to crap, especially so long before 200k miles.

Edited 6 hours ago by Wertbe

[Slartibartfast]

I had a weird clatter turn out to be the front bearing in the alt giving out. Remove the accessory drive belts, run it, see if the noise goes away. If you do them one at a time you'll know which one is noisy. I would also give the water pump a spin, see if there's anything obviously wrong there. 

 

Given the front-end wreck, I'd also check that the fan shroud is held on properly, and the fan isn't making contact with it. Long shot, but worth checking. 

 

If it still makes the noise with all the belts off, might be worth pulling the timing covers to check the belt tension and the condition of the idler pulley. IIRC the keyway only locates the sprocket during assembly, and it's clamped in place by the crank bolt. So unless the crank bolt is loose, it shouldn't be able to rattle.