RB25DET Neo Strange Noise

[Dyzzii]

Hi guys - Apologies if this is the wrong section

So recently had my R34 GTT tuned running an RB25DET neo. Tuner said that at around 5000rpm he can hear a noise when listening in through the knock sensor. The ECU is picking it up as knock sometimes but it isn't actually knock. He said its almost a metal-on-metal sounding noise, and it starts at 5000rpm and dissapears at 5.5 every single time. Cannot hear it from outside the car, only when listening in through the knock sensor.

I'm hoping for some help in narrowing down what it is. My dyno numbers are perfectly fine (will upload the sheet later tonight), power curve is stable etc. He believes it is something harmonic related as it is only at that RPM range. Have done runs with VCT disabled and it still makes it so that is not the culprit. He has suggested to me that it may be the intake cam gear although he's very rarely heard of them failing. 

My issue is they are a stupidly expensive part to replace for a "potential" fix. His other suggestions have been potential scoring on the cam lobes. Have you guys got any input on this? So noise starts every single run at basically dead on 5000rpm, stops at 5500. Almost a really fast " drdrdrdrdrdr" noise (best way i can describe it). One other thought by him was potentially a lifter.

Unsure if this matters, but the car's running an S2 RB25DET neo, nistune ECU, 14psi boost, front mount, full exhaust, cold air intake. Car is also only 104,000kms. Car still drives perfectly fine and would have had no idea anything was making noise had he not told me. 

Any advice would be greatly appreciated! 

[GTSBoy]

Could very easily be the VCT.  On/off makes no difference to it being broken enough to make a noise!

If it truly is a harmonic sort of thing, then the biggest culprit would be timing belt/tensioner.  Some aftermarket cam belts slap around like crazy.  Or the tensioner could be unhappy.

Would not suggest cam lobe scoring as likely to cause anything at all, let alone a noise that comes and goes at a certain rpm.

[Dose Pipe Sutututu]

On the topic of belts/idlers/pulleys

When was the last time the timing belt/major service was done? could well be bearing noise from either the water pump OR the idler OR the tensioner pulley

[Dyzzii]

The cambelt was done at around 90thousand. He's told me he doesn't think it's cambelt related as its a more metal-on-metal type noise. I did suggest the cambelt to him but he didn't seem to think so. Although a tensioner/idler would make sense for a metal noise. I'm unsure if the belt is a genuine Nissan one i'l have to check.

Is there a way to diagnose if one of the idlers is the culprit, or the VCT gears? He seemed pretty adamant that my VCT was not the culprit either. I was planning on taking the front cover off and having a look. But you can only hear this noise when listening in through the sensor, making it immensely difficult to pinpoint and diagnose. 

I don't want to go replacing components just for there to be a "chance" of it fixing. Any ideas of how to narrow this down? Or check if any of your suggestions could be the cause?

[iruvyouskyrine]

+

 

Will be you best friend trying to find strange engine noises.

[Dyzzii]

I tried giving that a shot, but holding the car at 5krpm made it super hard to actually hear anything over my exhaust :c. Couldn't really distinguish anything with the rpm that high unfortunately

[AngryRB]

Ive had some recent experience with similar, the vct was rattling metal on metal noise on cold start. 

Had a metal scraping noise too, this was simply the backing plate rubbing on the cam gear, not much holding it back, probably happens from someone leaning over the motor with a fat gut lol. 

 And finally another rub noise was the timing belt too tight, GL with it..

[Dyzzii]

14 hours ago, AngryRB said:

Ive had some recent experience with similar, the vct was rattling metal on metal noise on cold start. 

Had a metal scraping noise too, this was simply the backing plate rubbing on the cam gear, not much holding it back, probably happens from someone leaning over the motor with a fat gut lol. 

 And finally another rub noise was the timing belt too tight, GL with it..

Were your noises audible through just listening from outside the motor? As my biggest issue is that I cant actually hear anything... May take the cover off though and see if it is rubbing or something of the sort.

[GTSBoy]

What grade of oil are you using?  If there is scope to go a little heavier it might be worth a try.  The noise might be a gudgeon or something similar talking that might quieten with thicker oil.

[AngryRB]

7 hours ago, Dyzzii said:

Were your noises audible through just listening from outside the motor? As my biggest issue is that I cant actually hear anything... May take the cover off though and see if it is rubbing or something of the sort.

Yeah were quite loud noises at idle speed  my tuner says the vct gears are becoming a more common issue.  Id be shining a bright light around the backing plate, see if theres rubbing and also slacken the belt a touch if its a bit tight.

Edited October 5, 2018 by AngryRB

[Dyzzii]

4 hours ago, GTSBoy said:

What grade of oil are you using?  If there is scope to go a little heavier it might be worth a try.  The noise might be a gudgeon or something similar talking that might quieten with thicker oil.

I believe i'm currently running Fully synthetic 10w40. Just did an oil change less than 500kms ago. Are you meaning the gudgeon pin that holds the piston to the rod?

@AngryRB i'l give that a whirl this weekend and hopefully I have some luck!

[GTSBoy]

40 minutes ago, Dyzzii said:

Are you meaning the gudgeon pin that holds the piston to the rod?

Yup.  Along with a variety of other things that have very small clearances that can chatter if they're too big.

[Dyzzii]

So i’ve taken the CAS off and inspected it. Couldn’t see anything funny but there was some scoring on the part the CAS bolts into (see photos).

Cambelt didn’t seem overtight and was replaced at a Nissan dealer so assume that’s not the culprit.

Does this scoring look normal? Also couldn’t see any rubbing marks on the cover.

Thanks heaps for the help so far

[Robocop2310]

I had this happen to my RB26...turned out to be lose pulley's or worn out timing belt. Check both and also check radiator hosing and airbox/pod housing for any holes. 

Good luck. 

[Dyzzii]

Timing belt appears to be okay. May have to pull the cover off AGAIN and check the pulleys, but they looked fine at a quick glance. It was done recently.

[Dale FZ1]

On ‎10‎/‎6‎/‎2018 at 3:05 PM, Dyzzii said:

So i’ve taken the CAS off and inspected it. Couldn’t see anything funny but there was some scoring on the part the CAS bolts into (see photos).

Cambelt didn’t seem overtight and was replaced at a Nissan dealer so assume that’s not the culprit.

Does this scoring look normal? Also couldn’t see any rubbing marks on the cover.

Thanks heaps for the help so far

Replace the gasket/spacer in your upper cam belt cover, ie hole where the CAS passes through.  Stop contact/grinding on the CAS mount with proper clearance.  

[Dyzzii]

2 hours ago, Dale FZ1 said:

Replace the gasket/spacer in your upper cam belt cover, ie hole where the CAS passes through.  Stop contact/grinding on the CAS mount with proper clearance.  

Will do! Any idea where I can source one of these from? Or do I just use normal washers? 

As a side note, i've been lead to believe that the previous owner lied to me and that the cambelt has not been done. Inspection of the belt is showing marks that shouldn't be there. So either the cambelt hasn't been changed, or it has but the tension has been set incorrectly. Am going to do the cambelt again with a new idler, tensioner, waterpump and seals. Hopefully this remedies the issue...

Thanks heaps for the advice so far! Will update afterwards :).

[Dale FZ1]

3 hours ago, Dyzzii said:

Will do! Any idea where I can source one of these from? Or do I just use normal washers? 

As a side note, i've been lead to believe that the previous owner lied to me and that the cambelt has not been done. 

Try with Kudos Motorsport, or Nissan.

Cam belt is not a massively difficult job to replace, so if in doubt throw another one on.

[iruvyouskyrine]

On 10/9/2018 at 6:39 PM, Dyzzii said:

Will do! Any idea where I can source one of these from? Or do I just use normal washers? 

As a side note, i've been lead to believe that the previous owner lied to me and that the cambelt has not been done. Inspection of the belt is showing marks that shouldn't be there. So either the cambelt hasn't been changed, or it has but the tension has been set incorrectly. Am going to do the cambelt again with a new idler, tensioner, waterpump and seals. Hopefully this remedies the issue...

Thanks heaps for the advice so far! Will update afterwards :).

FYI timing belts deteriorate pretty quickly, not structurally but visually. Do a couple 1000km on a new belt and it looks very old very quick.