Weird noise between 1500-3000 rpm

[judasentinel]

Hi.

I'm worried about this noise from my 95 R33 GTR. It all started after a recent tune on the car. Had a front turbo failure (didn't break off, just became noisy). The car had Garrett 2860-9s. Only the front one went. Is that strange? What causes only the front to fail? When I removed the turbos, they moved freely but the front one had a clear internal grinding noise when I spun it by hand. I decided to put new turbos in and went for a brand new pair of 2860-s with upgraded internals.

After the turbos were installed, I came home and noticed this noise. I checked the oil and it was pitch black. Drained it out. Didn't find any copper or metal shavings in the oil filter.  Didn't check the oil itself in the drain bucket. It's gone now anyway. Put in new Shell Rotella 15W40 oil in it and new filter. The noise is still there. It is slightly lower when it really warms up, but it is still there. Oil pressure with stock gauge stays around 2 bar at idle and then goes  up to 4 bar when revving. Cold start it is between 5 and 6 bar on the stock gauge.

You can hear it as I rev the engine up and then it disappears somewhat after 3000 rpm.

I put a stethoscope on the car and it is the loudest on and around the front timing cover and near the front turbo.

Please help. I live in a small town in Montana, USA and there aren't many resources available to diagnose this, let alone fix it. SAU has been a resource for me since I got my first Skyline in 2006. I have read thru some posts about timing belt noise, etc., but I am not sure if it relates to timing belt or idler/tensioner or CAS.

Thank you for reading.

Edited January 12, 2023 by judasentinel
Added more info

[Duncan]

Sorry, but that sounds exactly like a spun rod bearing to me, particularly because it starts/increases with revs.

If so, every revolution the engine does is doing more damage

[judasentinel]

Thank you, Duncan. I thought as much too, but there was no metal in the oil filter. In addition, after 3200 rpm or so, the noise disappears. It doesnt get louder as the revs go up beyond a certain rpm. On idle, you do not hear anything at all. I hope I am right and you are wrong, but I do not know for sure.

Do you think there is a chance it may be something less sinister?

[Duncan]

Yes, there are other things that go roundy round that could cause an issue but I'm about 99% sure. 

As you said in first post that direct advice is hard to get locally you could catch some oil from the drain plug and get it analysed to confirm, the amount of bearing inclusions from a spun bearing will be immediately obvious

[judasentinel]

A few questions:

1. Should I be able to hear this at idle as well?

2. If I do not hear it at idle at all, and if I put a stethoscope to the bottom end somewhere, should it be more audible at the bottom than it is at the timing cover?

3. Does rod knock or spun bearing sound go away or diminish with the engine warm? That is what seems to be happening here. Once the car is warmed up, the noise is quite faint.

4. Also, at after 3500 rpm, you cannot hear it. And you can barely detect it even with a stethoscope. Possible that the frequency due to higher revolutions is so high that you are not able to distinguish it from other engine noises?

5. The oil filter filament when I changed the oil after I started hearing this noise showed no metal shards or shavings. Usually, you split the filter open, lay the louvered filament out flat and look for any copper shavings. I did not see anything. 

6. What causes front turbo failure on an RB26? Is this a known phenomenon due to oil-related issues or oil pump issues?

Thanks.

[GTSBoy]

33 minutes ago, judasentinel said:

What causes front turbo failure on an RB26? Is this a known phenomenon due to oil-related issues or oil pump issues?

Nothing causes front turbo failure in particular. Rear turbo failure is more common, for the known reasons.

So, yes, oil supply issues are the #1 suspect. But it can also just be dumb random luck on behalf of the turbo, and it could be caused by the turbo ingesting something (which doesn't happen without seeing signs of it on the compressor wheel).

[robbo_rb180]

33 minutes ago, judasentinel said:

A few questions:

1. Should I be able to hear this at idle as well?

2. If I do not hear it at idle at all, and if I put a stethoscope to the bottom end somewhere, should it be more audible at the bottom than it is at the timing cover?

3. Does rod knock or spun bearing sound go away or diminish with the engine warm? That is what seems to be happening here. Once the car is warmed up, the noise is quite faint.

4. Also, at after 3500 rpm, you cannot hear it. And you can barely detect it even with a stethoscope. Possible that the frequency due to higher revolutions is so high that you are not able to distinguish it from other engine noises?

5. The oil filter filament when I changed the oil after I started hearing this noise showed no metal shards or shavings. Usually, you split the filter open, lay the louvered filament out flat and look for any copper shavings. I did not see anything. 

6. What causes front turbo failure on an RB26? Is this a known phenomenon due to oil-related issues or oil pump issues?

Thanks.

My experience with rod knock was similar

1. Not always, depends on how bad bearing is
2. I couldn't hear mine at idle but noise was there as soon as throttle applied
3. My temps were fine
4.depends on the damage, how much bearing is worn
5. I coundn't see anything 
6. Never had it but had turbine fins hit my car

maybe a case of pull the engine and check it.

[Duncan]

Seeing a rod bearing has now failed, my money is on an underlying oil problem killing the front turbo too.

I'm not sure why the noise currently goes away around 3,200 but the longer you run the engine with the problem, the more likely you are to hear it at all revs (also, the more likely something from the spun bearing will cause further damage to other bearings, cam journals, oil pump etc etc.)

when a rod big end bearing is only just failing it is common for it to be OK when cold (thicker oil) and low revs (lower load on the bearing) - so noise increasing with revs and temp is a pretty sure sign of it being a big end bearing

don't forget to replace all of the oil coolers when you rebuild or replace the engine, in particular the oil/water cooler under the oil filter is easy to forget and expensive. It might be worth replacing it with a unit without the cooler (eg from a stagea or r31 skyline)

[judasentinel]

Thanks to everyone for your responses.

1. I have since removed the timing cover and found that the noise is particularly very loud when I put the stethoscope directly on the CAS (Cam angle sensor) itself or the metal bracket behind the CAS. It is also louder on the exhaust cam cover, and not so much on the intake cam cover. Also, the bottom end does not seem to have the noise when I put the stethoscope on the part of the engine block behind the idler and tensioner
2. Fearful of what Duncan said, I took some oil samples out and have sent them to a lab for analysis. Let's see what they say. Will know in 2 weeks or so. Two samples - one the current oil, which I just put in less than a month ago, and one from a month ago, from the time when the turbo had failed I recorded the sound clip in my original post
3. @Duncan, what "underlying oil problem" would cause the front turbo failure?
4. Why does the sound fade away with increased temperature or revs?
5. I don't have an aftermarket oil cooler in my R33 GTR, unless you are referring to the round thing with the lines/fins on it near the oil filter? If so, perhaps one can flush it and run some brake clean through it?
6. What water cooler are you referring to, @Duncan?
7. Also, is it advisable to flush both turbos with brake clean fluid as well? How do you flush out the rest of the engine of any debris IF there is any?
8. I may also replace the oil pump and piston rings, along with changing the timing belt, idler, tensioner and coolant pump

Thank you all. I will update this as we go along.

[Duncan]

3....too soon to tell. you should get your engine builder to disassemble the engine and see if they can determine a failure reason....

4. as the oil gets thinner bearings have less protection from touching the metal.

5/6 I am indeed talking about the round cannister under the oil filter (if the oil filter is in the standard location). Coolers are pretty much impossible to clean, I would not risk a new engine on a re-used cooler.

7. Yes, you should reverse flush the core of the turbos, and also the turbo oil feed and drain lines, as well as disassemble the oil pump to inspect and clean (probably worth replacing this depending on budget)

8. Yes, like 7 it will depend on budget but replacing water pump, timing belt, timing belt idler and pulley are all good ideas while it is apart. Same for things like cam cover, crank and rear main seals. They may all be re-usable but they are much cheaper to replace while the engine is apart than later.

[soviet_merlin]

2 hours ago, judasentinel said:

4. Why does the sound fade away with increased temperature or revs?

 

8 minutes ago, Duncan said:

4. as the oil gets thinner bearings have less protection from touching the metal.

Would you mind elaborating on that Duncan? Oil gets thinner when it gets warmer, and if that means less protection then there should be more noise not less, no?

[GTSBoy]

4 hours ago, soviet_merlin said:

Would you mind elaborating on that Duncan? Oil gets thinner when it gets warmer, and if that means less protection then there should be more noise not less, no?

It means the loaded running clearances are smaller (the thinner oil has less film strength to keep the surfaces separated) and so the crank pin/bearing does not have to move as far and therefore does not build up as much speed before it hits. This is presuming that the bearing is still/already knocking when it is cold. Thus, it would travel further and gain more speed with cold oil and make a louder noise when the surfaces smack together.

[judasentinel]

Hi everyone. Update: Found out thru oil analysis that there were some metal shavings in the oil. Front main bearing spun and the rest were all ok. At any rate, new oil pump (N1), new timing kit, new ACL 1 thousandth oversize main and rod bearing, new rings, new gaskets, and everything is put together.

Car started just fine but there is slight thumping sound up top near the timing cover area. The oil pressure is lower than it was before. Prior to the whole thing, I was using 15W40 Shell Rotella oil. Currently, it is running 5W30 conventional oil for the first 100 miles until I do a new oil change. Pressure is reading around 4-5 kg/cm2 upon cold start and then settles to around 1-1.5 kg.cm2 when warm. I know that is really low, but then I have no way of knowing the actual pressure because I don't have an aftermarket oil gauge. I do have an aftermarket pressure sender teed in, but don't know how to connect it to a gauge.

The mechanic who rebuilt the engine is at a loss as to why that slight thumping noise is there up top. It is not very audible at cold start but then it is there after it has warmed up. Revving the engine, it sort of disappears but it could be due to the noise. Also, he set the base timing to 18 degrees BTDC at around 1000 rpm.

I have spent close to $5000 on this and still not sure what this new slight thumping sound is. Doesn't sound like metal on metal, and it is not a whine. Engine seems to run smooth with a slight physical vibration. All cylinders are at around 150 psi cold compression, as per the mechanic.

If anyone has some ideas, please throw them my way. I will share them my mechanic.

Thank you.

[Duncan]

That is pretty hard to e-diagnose unfortunately. It might be worth removing the cam covers and timing cover to see if there are any fresh witness marks.

Re the oil pressure it is very much worth having a gauge or logging. What ECU do you have? If it can read a sender you need a sender and suitable wiring to the ECU (usually 5v, sensor earth and ECU input). If not or you want a separate gauge, any aftermarket electronic oil pressure gauge would be suitable, it will come with a sender, wiring and gauge to mount somewhere.  Any expensive new engine is worth having at least a proper gauge to monitor it.

With regards to your rebuild, it is unusual to have a main bearing spin. Hopefully your engine builder carefully checked it for any issues and had some feedback about likely failure cause like low oil pressure, I am concerned you might have had a bent crank and hope it was straightened OK if so because otherwise it will recur

[judasentinel]

Thanks, Duncan. The mechanic said that the crank looked fine. I am no expert, so cannot comment. He says he threw out the old bearings as many of them had some copper showing on them, but the front main one was more worn out. I dont know if it actually had spun out of position completely, because if that happened, the crank would have bent a bit. possibly. So I am not sure. He also said that the oil pump looked fine, but he replaced it anyway with the N1 pump. Again, I didnt see the old one as he said he threw it away.

I have a Link ECU, which does have the capability to read an oil pressure sensor's readings. I just don't know the exact wire to connect the sender to - 5v source, earth, etc.. I will do some research on it.

Hopefully, the mechanic can look behind the cam cover and identify if there is any indication. Could a timing of 18 degress BTDC at 1100 rpm cause that tiny bit of thumping noise to it? I know sometimes, retarded timing can cause an engine to run slightly rougher.

Interestingly, he was at a loss about why the engine failure happened. It was not a catastrophic failure at all. In fact, the car ran great till I stopped driving it. The only thing was that noise, which is not there anymore. I had a pair of Garfrett 2860-9s on this car, and the front one sseemed to have failed, and then after I replaced the turbos with new ones, this engine thing happened. So it is hard to say what caused what. The oil quality was bad.....I mena baadd. It was all black. He had to wash and clean the whole bottom end. He rehoned the cylinders, put new rings in, with the same pistons and rods and crank. He actually did a great job putting it together. I just dont know what could have been put together wrong.

 

I doubt there is any way to check if everything is working as it should, unless you put the engine back in, start it up and run it for a while. Otherwise, it is not possible for mere mortals to bench test an engine.

I am keeping fingers crossed that he will find the problem (if any) and it is a minor thing. Or better still, it is simply the timing kit settling in.

 

Once I know more, I will post the update. And when I go to his shop next, I will do my best to record the sound or make a video of it and post it here.

Keep it coming...thanks.

[joshuaho96]

1 hour ago, judasentinel said:

Thanks, Duncan. The mechanic said that the crank looked fine. I am no expert, so cannot comment. He says he threw out the old bearings as many of them had some copper showing on them, but the front main one was more worn out. I dont know if it actually had spun out of position completely, because if that happened, the crank would have bent a bit. possibly. So I am not sure. He also said that the oil pump looked fine, but he replaced it anyway with the N1 pump. Again, I didnt see the old one as he said he threw it away.

I have a Link ECU, which does have the capability to read an oil pressure sensor's readings. I just don't know the exact wire to connect the sender to - 5v source, earth, etc.. I will do some research on it.

Hopefully, the mechanic can look behind the cam cover and identify if there is any indication. Could a timing of 18 degress BTDC at 1100 rpm cause that tiny bit of thumping noise to it? I know sometimes, retarded timing can cause an engine to run slightly rougher.

Interestingly, he was at a loss about why the engine failure happened. It was not a catastrophic failure at all. In fact, the car ran great till I stopped driving it. The only thing was that noise, which is not there anymore. I had a pair of Garfrett 2860-9s on this car, and the front one sseemed to have failed, and then after I replaced the turbos with new ones, this engine thing happened. So it is hard to say what caused what. The oil quality was bad.....I mena baadd. It was all black. He had to wash and clean the whole bottom end. He rehoned the cylinders, put new rings in, with the same pistons and rods and crank. He actually did a great job putting it together. I just dont know what could have been put together wrong.

 

I doubt there is any way to check if everything is working as it should, unless you put the engine back in, start it up and run it for a while. Otherwise, it is not possible for mere mortals to bench test an engine.

I am keeping fingers crossed that he will find the problem (if any) and it is a minor thing. Or better still, it is simply the timing kit settling in.

 

Once I know more, I will post the update. And when I go to his shop next, I will do my best to record the sound or make a video of it and post it here.

Keep it coming...thanks.

No, considering the stock timing at idle is 950 rpm at 20 BTDC. Something is wrong. Narrowing down exactly where it's coming from is important, then getting eyes on if you can. Double check your gauge reading against another oil pressure gauge/sensor. Anything shedding debris will normally damage the turbos first as those are the most stressed bearings. Then they start shedding metal in response which causes a cascading failure.

[Murray_Calavera]

2 hours ago, judasentinel said:

The mechanic said that the crank looked fine.

Were measurements taken? You can't really eyeball a crank and say its in spec.

I'd be interested to see what was recorded, you can compare it with the specs in the workshop manual that I've attached. 

2 hours ago, judasentinel said:

I doubt there is any way to check if everything is working as it should, unless you put the engine back in, start it up and run it for a while. Otherwise, it is not possible for mere mortals to bench test an engine.

I don't know what is local to you, but an engine dyno would do exactly what your describing. Up to you if you think it's worth the cost and time to run the engine up on a dyno before it's put in the car. It's also a nice way to break in a freshly built engine.